A Thesis on
DESIGN OF COMPACT DGS SHAPED MICROSTRIP UWB BANDPASS FILTER BASED ON CIRCULAR STUB MMR FOR MOBILE COMMUNICATION
in Partial Fulfilment of the Requirements
for the Degree of
MASTER OF TECHNOLOGY
Electronics & Communication Engineering
Under the Supervision of
Prof. Kapil Kumar
Sanskar College of Engineering & Technology, Ghaziabad
Faculty of Engineering
DR. A.P.J. ABDUL KALAM TECHNICAL UNIVERSITY
(Formerly Utter Pradesh Technical University)
I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree of the university or other institute of higher learning, except where due acknowledgement has been made in the text.
Name: SAVITA YADAV
Roll No: 1621531501
Certified that Savita Yadav (Roll No: 1621531501) has carried out the research work presented in this thesis entitled “Design of Compact DGS Shaped Microstrip UWB Bandpass Filter based on Circular Stub MMR for Mobile Communication” for the award of the degree of Master of Technology from Sanskar College of Engineering & Technology, Ghaziabad, affiliated to Dr. A.P.J. Abdul Kalam Technical University, Lucknow under my supervision. The thesis embodies results of original work, and studies as are carried out by the student himself and the contents of the thesis do not form the basis for the award of any other degree to the candidate or to anybody else from this or any other University.
Date: June, 2018
Prof. Kapil Kumar
Associate Professor & HOD
Department of Electronics & Communication Engineering
DESIGN OF COMPACT DGS SHAPED MICROSTRIP UWB BANDPASS FILTER BASED ON CIRCULAR STUB MMR FOR MOBILE COMMUNICATION
In this thesis, An Ultra-wideband (UWB) – band pass filter (BPF) based on circular stub multi-mode resonator (MMR) is presented, which is formed by three stage circular stubs and cascading several open-circuited transmission line sections with a coupled-line section. We are also using the three arrowhead shaped defected ground structure (DGS) to enhance the performance of the filter. The performance analysis of proposed filter has been carried out using CST Microwave Studio on various radiuses of stubs. The best result is obtained for the pass band at the side stubs on radius 0.7 mm. The proposed filter exhibits pass band characteristics for the frequency range 3.6-10.45 GHz (Bandwidth-6.85 GHz) with minimum suppression of -62 dB. The constant group delay with maximum variation of 0.1 ns at the frequency of 3.7-10.6 GHz and good UWB performance makes it a selective candidate for various UWB wireless applications. A low profile microstrip band-pass filter design using two 0.7mm circular stub and parallel coupled lines is presented in this work. The two 0.7mm circular stub and parallel coupled resonator’s dimensions which are in 2 mm x 2 mm are calculated theoretically and the equivalent circuit is analysed. The filter is integrated with Defected Ground Structure (DGS) to alter current distribution over the ground plane and hence changing the resonance properties of the filter’s element. The proposed structure offers a simple and compact design while exhibiting wide stop-band characteristics in comparison with conventional coupled microstrip line filter design. The measured results agree well with the simulations and calculations data.
The introduction of DGS suppresses the second, third and fourth harmonic responses enhancing the stop band criteria. In addition, the DGS causes resonance frequency shift on some resonator elements, miniaturizing the length and make the overall size 65.8% more compact compared to the conventional ones. This thesis report is a stepwise synthesis procedure to design higher-order DGS based BPF with Butterworth structure on any suitable substrate in the range ?r=4.3 at design frequency and substrate height is H=1 mm. The recent circuit models are researched and closed structure definitions are displayed to calculate the region of the DGS slot heads for the given inductance. The enhancement in sharpness of the progress is up to 100 dB/decade.
The improvement in the 15 dB to 50 dB rejection bandwidth is up to 3.7 GHz to 10.6 GHz. The group delay response of Butterworth BPF is better than that of Chebyshev BPF. The study also presents the design results of the UWB DGS-type BPF at the cut-off frequencies of 3.7 GHz to 10.6 GHz. Return loss in pass band is less than 15dB. DGS is built from 3 arrow head structure. The equivalent circuit of BPF comprises of lumped elements of inductor and capacitor and is performed using EM & Circuit simulator. From the characterization, the measured result is agreed qualitatively with the simulated result of equivalent circuit. The characteristic of realized BPF which is comparable with the simulation result has -3dB working bandwidth of 3.7 GHz to 10.6 GHz.
I would like to express my sincere gratitude and personal regards to my guide Prof. Kapil Kumar, Associate Professor & HOD, Department of Electronics & Communication Engineering, SCET, Ghaziabad for his invaluable constant supervision and appreciation during the entire research work and preparation of manuscript.
I would like to express my reverence and gratitude to my family, my friends whose love, inspiration and encouragement helped me tide over the difficulties I had during the project.
Date: June, 2018
Place: Ghaziabad Savita Yadav
(Roll No: 1621531501)
TABLE OF CONTENTS
List of tables ix
List of figures x
List of abbreviations xiii
1. CHAPTER 1: INTRODUCTION 1-16
1.1 Introduction 1
1.2 Need and Motivation of UWB BPF 3
1.2.1 The Usage of UWB Filters 5
1.2.2 Application of BPF 7
1.2.3 The Scattering Matrix and UWB BPF Characteristics 7
1.3 Planer Technology 8
1.4 Microstrip Transmission Line 8
1..4.1 Definition 8
1.4.2 Application and Characteristics of Microstrip Lines 9
1.5 Filter Bandwidth Improvement Techniques 9
1.5.1 parallel coupled lines microstip bandpass filter 9
1.5.2 Tapped Input and output coupled lines 10
1.5.3 Impedance Transformation 11
1.5.4 Low Dielectric Constant Material/Thicker Substrate 11
1.5.5 Multiline Couplers 11
1.5.6 Sufficient Number of Resonator Sections 12
1.5.7 Half Wavelength Separated Shorted Resonators 12
1.5.8 High Pass – Low Pass Filter Combination 12
1.6 Utilizing Defected Ground Structures (DGS) 13
1.6.1 DGS Element Characteristics 14
1.7 Statement of the Problem 15
1.8 Objective 15
1.9 Outline of Chapters 16
2. CHAPTER 2: LITERATURE REVIEW 17-19
2.1 Introduction 17
2.2 Literature Review 17
2.3 Findings of Literature Review 17
2.4 Research Gaps 19
3. CHAPTER 3: THEORY AND DESIGN 20-28
3.1 Introduction 20
3.1.1 Filter Definition 20
3.1.2 Classification of Filters 20
3.3 High Pass Filter 21
3.4 Low Pass Filter 22
3.5 Band Pass Filter 23
3.5.1 Development of UWB Band pass Filters 23
3.5.2 Microstrip multi-mode resonator with two parallel-coupled lines at two ends 24
3.6 Expressions Used in Filter Design Process 24
3.6.1 Scattering Parameter 24
3.6.2 Insertion Loss 25
3.6.3 Reflection Loss 25
3.6.4 Q Factor 26
3.6.5 VSWR 27
188.8.131.52 Physical Meaning of VSWR 27
3.6.6 Group Delay 28
3.6.7 Pass band 28
3.6.8 Cut-off Frequency 28
3.6.9 Stop band 28
3.6.10 Ripple 28
3.6.11 Bandwidth 28
3.6.12 Rejection 28
4 CHAPTER 4: METHODOLOGIES AND DESIGN PROCEDURE 29-32
4.1 Desired Approach 29
4.2 Problem Formulation 29
4.3 Design Methodology 29
4.4 Design Specifications 29
4.5 Flowchart of Design Procedures 30
4.6 Experimental Setup 31
4.7 Calculation Setup 32
4.8 Theory of Schematic UWB BPF 32
5 CHAPTER 5: RESULT & DISCUSSION 33-41
5.1 Introduction 33
5.2 Desired Specifications 33
5.3 Simulation Setup 33
5.4 Graphical Analysis 33
5.5 Circuits and their Graphs 33
5.5.1 Analysis and comparison of 5 pole simply designed BPF and 5 pole BPF design by cascading HPF and LPF 33
184.108.40.206 Analysis of 5 pole BPF design by cascading HPF and LPF 33
220.127.116.11 Analysis 5 pole simply designed BPF 35
5.6 Introduction of DGS for Enhancement of performance 35
5.7 Proposed Wide Band band pass filter Result Discussion 36
5.8 Result and Discussion 40
5.9 Result summary 40
6 CHAPTER 6: CONCLUSION & FUTURE WORK 41
7 REFERENCES 42
8 LIST OF PUBLICATIONS 45
9 CURRICULAM VITAE 46
LIST OF TABLES
1 5 Pole BPF elements Table 5.1 34
2 overall result summery Table 5.2 40
LIST OF FIGURES
1 An UWB transmitter block diagram Fig. 1.1 1
2 An Ideal BPF Fig. 1.2 2
3 RF/microwave spectrums Fig. 1.3 2
4 FCC Frequency Mask for UWB Applications Fig. 1.4 3
5 Representation of UWB pulses Fig. 1.5 4
6 UWB system: (a) Transmitter, (b) Receiver, (c) Licensed and unlicensed band around the UWB spectrum, (d) FCC mask Fig. 1.6 6
7 View of a Microstrip Line and Its Lines of Electric and Magnetic Fields, (a) Whole View, (b) Zoom in. Fig. 1.7 9
8 General Structure of Parallel Coupled-Line Microstrip Bandpass Filter. Fig. 1.8 10
9 Tapped Input Fig. 1.9 10
10 Filter sample with tapped input section (removed coupled input section) Fig. 1.10 11
11 Coupled Lines with impedance transforming section Fig. 1.11 11
12 Multiline coupled line filter sample Fig. 1.12 12
13 Quarter wavelength shorted stub separated by half wavelength lines Fig. 1.13 12
14 UWB filter with A Low Pass / High Pass filter combination Fig. 1.14 13
15 There are the different DGS geometries which have been designed till now Fig. 1.15 14
16 Different DGS resonant structure configurations. Fig. 1.16 15
17 Base paper work Fig. 2.1 19
18 Desired project work Fig. 2.2 19
19 Frequency Responses of the Four Types of Filters Fig. 3.1 20
20 An active high-pass filter Fig. 3.2 21
21 Band pass filter Fig. 3.3 23
22 The Schematic of a Micro Strip Multi-Mode Resonator (MMR) with Two Parallel Coupled Lines at Two End Fig. 3.4 24
23 Two port network Fig. 3.5 24
24 Voltage Measured Along a Transmission Line Fig. 3.6 27
25 Generic Attenuation Profile for a Bandpass Filter Fig. 3.7 28
26 The Flowchart of Design Procedure Fig. 4.1 30
27 project options Fig. 4.2 31
28 add measurement Fig. 4.3 31
29 Calculation setup using TXLINE option Fig. 4.4 32
30 Schematic of UWB BPF using Lumped elements Fig. 5.1 34
31 Simulated Graph showing Insertion loss S21and return loss s11 for cascaded BPF Fig. 5.2 34
32 Schematic of UWB BPF using Lumped elements Fig. 5.3 35
33 Simulated Graph showing Insertion loss S21and return loss s11 for simple BPF Fig. 5.4 35
34 DGS Structure with Three Arrowhead Shape Fig. 5.5 36
35 Proposed MMR Based UWB Filter structure Fig. 5.6 36
36 Return loss analysis in Pass band Fig. 5.7 37
37 Pass band results of proposed UWB filter Fig. 5.8 37
38 Simulated Graph showing Insertion loss S21and return loss s11 for wide band BPF on CST Microwave studio Fig. 5.9 38
39 Simulated Graph showing VSWR for Ultra Wide Band BPF on CST Microwave Studio Fig. 5.10 38
40 Simulated Graph showing group delay for ultra wide band BPF on CST Microwave studio Figure 5.11 39
41 Simulated Graph showing Eye diagram for ultra wide band BPF on CST Microwave studio Figure 5.12 39
42 Simulated Graph showing Magnetic field for ultra wide band BPF on CST Microwave studio Figure 5.13 40
LIST OF ABBREVIATIONS
1 DGS Defected Ground Structure
2 BPF Band Pass Filter
3 SNR Signal to Noise Ratio
4 LPF Low Pass Filter
5 HPF High Pass Filter
6 VSWR Voltage Standing Wave Ratio
7 FCC Federal Communication Commission
8 AWR Applied Wave Research
9 DUT Device Under Test
10 RF Radio Frequency
11 DC Direct Current
12 AC Alternating Current
13 SWR Standing Wave Ratio
14 PCB Printed Circuit Board
15 CPW Co Planer Waveguide
16 PCS Personal Communication Service
17 WLL Wireless Local Loop
18 CST Computer Simulation Technology
19 ISM Industrial, Scientific & Medical
20 GPS Global Positioning System
21 SS Spread Spectrum
22 WPAN Wireless Personal Area Network
23 RFID Radio Frequency Identification
24 LOS Line of Sight
25 MMR Multiple-Mode Resonator
26 UWB Ultra Wide Band
27 LNA Local Area Network
28 GHz Giga Hertz
29 MHz Mega Hertz
30 KHz Kilo Hertz
In the current scenario, Ultra-Wideband (UWB) communication system offers numerous wideband applications such as microwave medical imaging, Ground Penetrating Radar (GPR) and RFID tag for inventory control and asset management. Always compact and inexpensive UWB transceivers are required for such wireless applications. Therefore UWB transceivers should be compact and inexpensive 1 .An UWB transmitter with different blocks is depicted in Figure 1.1, where the input data are encoded, modulated, and multiplexed at the chip level, and then the multiplexed pulse is transmitted by a UWB antenna after reshaping and amplifying at the package level.
Fig. 1.1 An UWB Transmitter Block Diagram
In this thesis extended version of MMR is used and proposed a novel microstrip line UWB band pass filter using Defected Ground Structure (DGS). Bandpass filters are utilized fundamentally in wireless transmitters and receivers. To limit the bandwidth of the output signal to the less important to transmit data at the desired speed and in the desired form is the primary function of such filters in a transmitter. And a bandpass filter permits signals inside a selected range of frequencies to be used or decoded, while preventing signals at undesirable frequencies from traversing in a receiver. A bandpass filter also additionally enhances the SNR ratio (sensitivity) of a receiver. In both at the source and destination uses, bandpass filters, having the maximum bandwidth for the mode and speed of communication being utilized to add the more signals that can be transferred in a system, while reducing the interference or disputes among signals.
Fig.1.2 An Ideal BPF
The output signal power falls to half of its level at the centre frequency f0 of the filter at the cut off frequencies, f1 and f2. The f2 – f1 which is the bandwidth of the filter is expressed in hertz (Hz), kilohertz (kHz), megahertz (MHz), or gigahertz (GHz).The area between cut off frequencies f1 and f2 is known as the filter passband. Microwave bandpass filters give a response signal just at a precise (narrow) frequency band. Additionally, the filter can be tuned to a precise frequency band with using different filter for each precise frequency band. The performance of a filter decides a viable utilization of a frequency which is essential asset in the field of communication. A bandpass filter enables a narrow band of frequencies to transmit through it unattenuated, and notch all other frequencies. This narrow band of frequencies are defined as a filter passband. The band pass filters designed in the microwave range play a crucial role in the pre selection of individual channels in the satellite communication technique.
Fig. 1.3 RF/microwave spectrums
1.2. NEED AND MOTIVATION OF UWB BPF
UWB BPF are sometimes utilized as a part of wireless communication system, A UWB band-pass filter is a key passive component of ultra-wideband (UWB) radio innovation which has received much consideration, both in academic and manufacturing fields. Because of its less price, massive information transmission rate and low power utilization, it has turned out to be exceptionally alluring in LAN, position location, tracking, and radar systems. A latest advancement in broadband wireless communication, the design of ultra wide band-pass filters is creating a great enthusiasm. Ultra-wideband techniques utilize wireless innovation equipped for transmitting information over a wide range of frequency bands for short distances with low power and high information rates. They are utilized for the activity of sending and getting very short bursts of RF signal. The UWB techniques have excellent capacity for uses that require precision distance or positioning calculations and additionally high speed wireless availability. The UWB innovation conveys high information rates more than 100 Mbps up to 1Gbps. The UWB waves can infiltrate through walls and different obstructions. The important features of the UWB techniques over narrowband techniques are high information rate because of the wide bandwidth, low cost, less power consumptions, and invulnerability to multipath. A UWB duplex system incorporates a digital and a RF hardware. The RF hardware, that is fundamentally a RF front end, incorporates a low noise amplifier (LNA), a microwave filter, an antenna, and matching devices with the required bandwidth. In this dissertation, UWB microstrip filters utilized as a part of a UWB RF front end modules are examined. Configuration difficulties and performance enhancement methods to accomplish a filter that conforms to the FCC characterized spectral mask for UWB techniques are explored.
In 2002, the Federal Communications Commission (FCC) affirmed the utilization of broad band (UWB) from 3.1 GHz to 10.6 GHz for business communication uses. As per the FCC indoor cutoff that is found in Fig 1.4.
Frequency Mask mainly requires the following rejection for an UWB filter design:
• -10 dB minimum rejection at 3.45 GHz
• -10 dB minimum rejection at 10.6 GHz
Fig 1.4 FCC Frequency Mask for UWB Applications
The UWB radios typically communicate with short pulses or cycles on the order of nanoseconds, spreading their energy over a wide range of bandwidth, as opposed to modulated sinusoids whose energy is localized around a single frequency .A sample pulse is shown in Fig.1.5 below. The impulse radio UWB transmits data based on the transmission of very short pulses with several Gigahertz bandwidths.
Fig.1.5 Representation of UWB pulses
UWB signalling has numerous qualities that make it appealing for an extensive variety of uses; from ultra-low-power RFID labels and wireless sensors to steaming wireless interactive media and wireless USB at a more prominent rate than1Gb/s. The high information rate multimedia home networks or child locator applications are a couple to name. The UWB is viewed as the most effective innovation for short range wireless interface between digital devices. Numerous applications in wireless innovation have been centred on narrowband executions. Innovation prerequisites on UWB techniques exhibit contrasts from the narrow band ones. Nevertheless, silicon and hardware enhancements, challenges in programming and algorithms for proficient information transmission and system administration are the specialized difficulties that ought to be taken up by this new innovation.
Ultra-wideband (UWB) techniques essentially enables the following wireless communication systems:
Short-distances (up to 10 m), higher information rates (up to 1 Gbits/s) applications, for example, the IEEE 802.15.3a (WPAN) standard working at 3.1-10.6 GHz.
Long-distances (up to 100m), lower information rates (up to 1 Mbits/s), e.g. remote sensor systems working at frequencies below 960 MHz.
For an abnormal state of sending in short and long ranges, low cost, less power consumptions are required. Low operating frequency gives extra preferences of through-wall capability and lower circuit power utilization that makes UWB appropriate for wireless sensor network in which battery life is an essential concern and line-of-sight (LOS) communication is favoured for ranging and positioning functionality. Due to wideband prerequisites of the UWB duplexer’s RF front-end, it is very difficult to design a RF front-end receiver with required electrical specs. In many applications, it is alluring to acquire the following:
wideband matching to a 50 ? antenna and ?lter,
low power utilization,
To gain ?atness over the whole frequency range of interest is important to meet the design speci?cations.
These features are the foundations of the wideband receiver front-end which a?ect the all over broadband communication system qualities. UWB innovation modulates impulse based waveforms rather than consistent carrier waveforms. As clarified over, the standards of UWB are to a very short pulses, and low duty cycle at time domain. For frequency domain, ultra wide range, low power spectrum density, and satisfactory obstruction with different users are fundamental standards. Exchanging higher information rate at low power with higher bandwidth, it isn’t changed by ordinary RF. Additionally, it empowers frequency reuse as 3.1-10.6 GHz coexist with different users. The multipath immunity is in the order that path delay is significantly more prominent than pulse width.
The UWB systems are generally computerized, simple analog modules that maintain low cost. UWB offers an answer for bandwidth, cost, physical size, and power utilization for next generation prerequisites. UWB varies subsequently from conventional narrowband radio frequency (RF) and spread spectrum innovations (SS), for example, Bluetooth Technology and 802.11a/b/g. A UWB transmitter sends billions of pulses over a wide range of frequency in a few GHz in bandwidth. The corresponding receiver changes pulses into information by tuning in for a familiar pulse arrangement sent by the transmitter. UWB’s mixer of larger ranges, lower power and pulse information enhances speed and diminishes obstruction with different wireless spectra .Based on FCC’s directions the UWB radio transmissions can legitimately work in the range from 3.1 GHz up to 10.6 GHz, at a constrained transmit energy of – 41dBm/MHz. The result is short-range channel capacity and limited interference, however the UWB gives sensational channel limit at short range that limits interference.
1.2.1 The Usage of UWB Filters
Transmitter and receiver block diagram of a RF front end, licenced and unlicensed bands alongside the FCC mask are appeared in Fig.1.6. A RF front end basically comprises of a low noise amplifier, a filter, and an antenna. This dissertation show the design of the UWB microstrip filter which can be utilized in this UWB RF front end module.
To transmit or get a high quality, a UWB bandpass filter must have the following features:
Typical bandwidth of 20% or 500 MHz or more noteworthy
A high selectivity to dismiss signals from existing frameworks, for example, 1.6 GHz Global Positioning System (GPS), 1.9 GHz cell band, and 2.4 GHz ISM band operating systems.
In the current decade, the UWB systems have been produced and used widely. Keeping in mind the end goal to meet the FCC details, a great selectivity at both lower and higher frequency ends and flat group delay output over the entire band are required.
Fig. 1.6 UWB system: (a) Transmitter, (b) Receiver, (c) Licensed and unlicensed band around the UWB spectrum, (d) FCC mask
Bandpass filters are two-port equipments that give transmission at frequencies inside the passband of the filter and removal of different frequencies outside of the band. A band pass filter is utilized to remove the interference of signals and effectively use a frequency. A bandpass filter is the parts utilized at the mobile radio communication base station, for example, a cell phone, a Personal Communication Service (PCS) and a Wireless Local Loop (WLL), and a radio frequency (RF) band. The part which a bandpass filter is to satisfy is transmitting to some loss signals which lie in a required frequency band while blocking all other frequencies outside the required band. A bandpass filter uninhibitedly passes frequencies inside determined range, while blocking frequencies outside the band, and can be intended to give symmetric or asymmetric properties. In microwave communication, the microwave frequency range has turned out to be crowded and has been subdivided into an immense number of various frequency bands.
1.2.2 Applications of BPF
Bandpass filters are generally utilized as a part of wireless transmitters and receivers. The principle function of such a filter in a transmitter is to limit the bandwidth of the response to the band allotted for the transmission. This controls the transmitter from mixing with other stations. In a receiver, a bandpass filter permits signals inside a coverage area of frequencies to be heard or decoded, while removing signals at undesirable frequencies from overcoming. A bandpass filter also improves the SNR ratio and sensitivity of a receiver.
In both at the source and destination uses, bandpass filters, having the maximum bandwidth for the mode and speed of communication being utilized to add the more signals that can be transferred in a system, while reducing the interference or disputes among signals.
Outside of electronics and signal processing, one case of the utilization of band-pass filters is in the climatic sciences. It is basic to band-pass filter latest meteorological information with a period scope of, for instance, 3 to 10 days, so just storms stay as variances in the data fields.
1.2.3 The Scattering Matrix and UWB BPF Characteristics
It is essential to first have a comprehension of the scattering matrix and how it can be utilized to decide control divider attributes. The scattering matrix, or S-matrix, is utilized to relate voltage waves incidents on device ports to voltage waves reflected from device ports, considering both magnitude and phase. The general equation of S-Parameter is given as
A vector network analyzer is regularly used to measure these parameters. For devices with more than two ports, for example, a power divider of three ports and any ports not part of the estimation are ended with matched load. Input impedance is matched to the characteristics impedance of the system then no power is reflected back to the same port for this purpose we design a ?/4 line which gives the better result in pass band as well as stop band. These identical impedances result in a reflection coefficient equivalent to zero, implying that any wave incident on the matched port won’t be reflected, or leave the port. Accordingly the reflected voltage at that port will be equivalent to zero. At the point when a device is matched at each of its ports, the diagonal components of its S-matrix to decrease zero.
One basic properties found in power dividers and additionally different devices is that of reciprocity. A reciprocal device is one in which the power transmitted between two ports of a system or device is the same paying little respect to the direction of propagation through the system or network. Another property of the S-matrix is how much loss can be credited to the network itself. It has been appeared on numerous events, especially by Pozar, that if the S-matrix of a network is unitary, the network is lossless. Besides, a unitary network suggests that the sum of the squares of the elements in a column of the matrix is equivalent to one. Isolation between the output ports of a power divider is also basic to network performance. Isolation is characterised as the ability of a signal at one port to not influence, or isolated.
Scattering matrices are also used to describe multiport networks, particularly at high frequencies. They are utilized to show microwave networks, for example, amplifiers and circulators, and are effectively identified with ideas of gain, loss and reflection. The scattering parameters show ratio of voltage waves entering and leaving the ports.
The S-matrix for an n-port system contains n2 coefficients (S-parameters), every one showing to a feasible input-output path. The number of columns and row in an S-parameters matrix is equivalent to the number of ports.
For the S-parameter subscripts “ij”, “j” is the port that is excited (the input port) and “i” is the output port. S-parameters are difficult (i.e. they have magnitude and angle) because both the magnitude and angle of the input signal are changed by the system. (This is the reason that they are sometime alluded to as unpredictable scattering parameters).
1.3 PLANER TECHNOLOGY
The use of a planer technology is a solution to solve problems according to voluminous structures spectral occupation and heavyweight. The weakness of planer circuits is that, it presents very important insertion losses than voluminous topologies.
However, contrary to voluminous technologies, the realization of microstrip transmission lines simplify the interconnections. It is used as well in printed circuit technology than integrated circuit technology.
1.4. MICROSTRIP TRANSMISSION LINE
Microstrip transmission line is the most popular and used planar transmission line in Radio frequency RF applications, exploited for designing certain components like filters, couplers and transformers. The wave type propagating in this transmission line is a quasi- Transversal electromagnetic wave “quasi-TEM” (see appendix N°01). The microstrip transmission line consists of metallic strip of width W and the thickness t, metallic ground and between it dielectric substrate with constant ?? of thickness h, as shown in the Figure 1.7 .The characteristic impedance ?? of the line is determined in terms of width W, thickness t and dielectrics substrate constant ??.
Fig. 1.7 View of a Microstrip Line and Its Lines of Electric and Magnetic Fields, (a) Whole View, (b) Zoom in.
Both electric and magnetic fields are present in the transmission lines. These fields are perpendicular to each other and to the direction of wave propagation for TEM mode waves, which is the simplest mode and assumed for most simulator except for microstrip line which assume ”quasi-TEM”, which is an approximated equivalent for transient response calculations).Electric field is established by a potential difference between two conductors: implies equivalent circuit model must contain capacitor. Magnetic field induced by current flowing on the line: implies equivalent circuit model must contain inductor.
1.4.2 Application and Characteristics of Microstrip Lines
Microstrip lines can be used in the manufacturing of some microwave components, therefore UWB filters can be made from them. Due to some suitable features, microstrip line is widely used (regardless of low power handling capacity) in the transmission of microwave frequency signals. The features may include:
Its simple geometry;
Small size and low cost;
Absence of difficulties in devices integration and mass production;
Good repeatability and reproducibility.
1.5 FILTER BANDWIDTH IMPROVEMENT TECHNIQUES
1.5.1 Parallel Coupled Lines Microstip Band pass Filter
Parallel-coupled microstrip bandpass filter is one of the most popular BPF and can be applied in many applications of microwave communication systems. General coupled bandpass filter is shown in Figure.1.8 illustrates a general structure of parallel coupled-line microstrip bandpass filter that uses half wavelength line resonators. This parallel arrangement gives relatively large coupling for a given spacing between resonators, this filter structure is particularly convenient for constructing filter having wider bandwidth as compared to the other structure.
Fig.1. 8 : General Structure of Parallel Coupled-Line Microstrip Bandpass Filter.
The filter structure is open circuited coupled microstrip lines. The components are positioned so that adjacent resonators are parallel to each other along half of their length. The resonators are coupled by means of gap capacitances between the resonator sections. This parallel arrangement gives relatively large coupling for a given spacing between resonators and making this filter structure particularly convenient for constructing filters having a wider bandwidth as compared to other type of bandpass filter.
1.5.2. Tapped Input and output coupled lines
Wide band coupled line filters more often than not require a tight coupling at the input and output coupled line segments. The tight coupling is normally not feasible for most microstrip line filters. Tapping the input and output of a coupled line filters gives a chance to remove the tightly coupled first and last coupler areas. See Figs.1.9 And Fig.1.10.
Fig. 1.9 Tapped Input
Fig. 1.10 Filter Sample with Tapped Input Section (Removed Coupled Input Section)
1.5.3. Impedance Transformation
A proper impedance transformation at input / output of a coupled line filter
Enhance the bandwidth of the transmission lines 12 as shown in Fig 1.11.
Fig 1.11 Coupled Lines with Impedance Transforming Section
1.5.4. Low Dielectric Constant Material / thicker substrate
Using low dielectric constant substrate or thicker substrate makes the high impedance lines feasible to realize and remove very narrow lines. This also provides better results in wider and realizable coupler gaps.
1.5.5. Multiline Couplers
Using multiple line coupled lines takes part in increasing the coupled power which gives higher coupling ratio. And every line section sums up the power making a higher coupling and higher bandwidth possible.
Fig. 1.12 Multiline Coupled Line Filter Sample
1.5.6 Sufficient number of resonator sections
In order to get broad bandwidth, an efficient resonator sections must be used. The resonator parameters are estimated by the well-known polynomial equations such as Chebyshev, Butterworth, Elliptical types.
1.5.7 Half Wavelength Separated Shorted Resonators
Quarter wave short stubs separated with half wavelength inverters give a very broad bandwidth.
Fig. 1.13 Quarter Wavelength Shorted Stub Separated by Half Wavelength Lines
1.5.8. High Pass – Low Pass Filter Combination
Joining and cascading high pass and low pass filters advantageously, as appeared in Fig.1.14, give a good answer for a wideband execution. The new consolidated filter operate like one band pass filter with more prominent bandwidth.
Fig. 1.14 UWB filter with A Low Pass / High Pass filter combination
1.6. UTILIZING DEFECTED GROUND STRUCTURES (DGS)
Ultra-wideband band pass filters (UWB BPF) play an important role in the development of UWB systems. So, with the enlarging in filter application in wireless communication systems, different techniques have been used to develop these UWB filters. Generally, lumped-element filter design is unpopular since the difficulty of its use at microwave frequencies along with the limitations of lumped-element values. Designers needed a new procedure and structure to make low insertion loss and perfect convention between simulated and experimental results. Introducing Defected ground structure (DGS) technique is one of the key solutions to realize the superior performances. Various new concepts have been associated with distributed microwave circuits in recent years, one such technique is DGS A structure in which our defect ground plane of microstrip or coplanar waveguide circuit to improve the performance. The word “defect” has been used in the DGS, to provide measurement of a perfectly conducting and infinite current sink. Clearly, a ground plane at extremely high frequencies (EHF) is far ousted from appreciating perfect ground behaviour. Notwithstanding the way that the additional disturbances of DGS change the conformity of the ground plane. In recent years, a defected ground structure is a very interesting method to miniaturize the size of microwave components. Regardless, to improve the performance of microwave /millimetre components, a steady research is going with this approach. From the photonic band gap structures (PBG) in the optics, the concept of DGS is begun. By etching different shapes in ground plane, the DGS is formed. The current path in the ground plane is disturbed by defects patterns which improve the performance of microstrip line or coplanar waveguide. The slow wave effect and notch characteristics are two important characteristics of DGS. By changing the shapes and sizes of DGS, these characteristics can be changed. A novel DGS is designed, fabricated, and used to remove the spurious harmonics of a class of multiband filter by using a predominantly magnetic coupling. By forming the slots on the ground plane and maintaining the original filter structure unaltered, we are able to design a one-pole lowpass filter.
The utilization of different DGS geometries has been presented in the paper, for example, spiral, rectangular, circular, square, dumbbell, U-shaped, hairpin DGS, V-shaped, L-shaped, concentric ring, hexagonal, arrow head slot, cross shaped, interdigital DGS and so forth as appeared in figure 1.15. The shielded current distribution in the ground plane is perturbed due to the different shape and dimension of the defect made in ground plane and because of this controlled excited electromagnetic waves propagate within the substrate layer.
Fig. 1.15. There are the different DGS geometries which have been designed till now.
1.6.1. DGS Element Characteristics
Under a transmission line, the resonant gap or slot in the ground plane is the essential element of DGS, adjusted for proper coupling to the line. Figure 1.16 shows various resonant structures that might be utilized. All are differing in area, equivalent L-C ratio, higher-order responses, coupling coefficient and other electrical parameters. A researchers will pick that structure which provides efficient result for the specific application.
Fig. 1.16. Different DGS Resonant Structure Configurations.
1.7. STATEMENT OF THE PROBLEM
Innumerable BPF have been designed and constructed, especially in recent years because of more complex simulation software and simplified fabrication techniques (i.e. microstrip). Moreover, novel UWB BPF designs have been produced that permit double and broadband frequency operation. Designs that uses wide range transmission of frequency to diminish layout size while keeping up a good bandwidth have also been created. This dissertation does not really look to build up a novel device, but rather to design, build, analyse, and better comprehend a microstrip UWB BPF.
Utilizing CST microwave studio suite software, a basic RF simulator, an idealized UWB BPF can be simulated to help determine practical values for S-parameter, return loss, isolation and bandwidth.
The objective of this thesis is to design an UWB BPF filter with wideband characteristics using MMR technique and DGS structures. The MMR techniques is not only offer low insertion loss as well as better matching with transmission line. By adding the short- and open-circuited stubs at input/output ports for impedance matching, the performance of the filter can be improved further. Also by the DGS implementation the filter characteristics is enhanced. There for good pass band behavior, the compact structure of proposed filter is best suitable for recent mobile applications.
The objectives of this thesis summerise as,
To design an UWB BPF using circular stub MMR and DGS to enhance the filter performance which follow the UWB frequency range provided by FCC.
To analyse the performance of the designed filter in terms of frequency response, S-parameter, group delay, VSWR, EM spectrum etc.
Analysis of simulation result to make suitable for mobile communication
1.9. OUTLINE OF CHAPTERS
Chapter 2 of this thesis covers the literature survey, research gap and literature review of the thesis. Chapter 3 contains a brief discussion on the theory and how it applies to the design UWB BPF using HPF and LPF. Simple simulations and ideal UWB performance are also presented to get a better idea of the limitations of the device. Chapter 4 discusses the design, construction methods of the UWB BPF. Chapter 5 discusses the knowledge gained from the previous design and how it was used to improve the next designs. It also presents the design, construction, and results of different pole BPF and how their performance is compared to each other. The final chapter 6 helps to validate the results obtained and provides a brief discussion on the conclusions drawn from this study and potential future work.
In this dissertation, ultra-wideband (UWB) microwave filters design and fabrication complexities are examined and, a microstrip UWB filter prototype design is presented. The UWB bandpass filter working in the 3.7 GHz to 10.6 GHz frequency band is focused to conform to the FCC spectral mask for UWB systems. A bandpass filter provide a narrow band of frequencies to transmit through it unaltered, and suppress out all other frequencies. This narrow band of frequencies is known as the filter’s passband. The band pass filters used in the microwave range play a very crucial role in the preselection of individual communication channels in the satellite communication systems. In this thesis BPF is designed by cascading High Pass Filter and Band Pass Filter. Joining and cascading high pass and low pass filters easily, give an accurate response for a wideband performance. The new consolidated filter operate like one band pass filter with larger bandwidth. The circuit is first simulated and optimized by utilizing microwave CST simulation software tools.
2.2 LITERATURE REVIEW
Researchers have managed to develop an UWB BPF with an excellent filtering performance with a very simple structure .The BPF using broadside coupled microstrip coplanar waveguide structure provided excellent UWB filtering performance in terms of its insertion loss, reflection loss and group delay compared to other works . Further research on this structure was, done, and a more functional bandpass filter was developed which not only operates over wideband but also has the capability to reject some frequency band. This work provided promising dual band Ultra wideband filter which enabled the possibility of avoiding interference between UWB radio system and existing narrow band radio systems. In this paper a new method to design UWB BPF using a combination of an open-circuited low pass and short circuited highpass filter is proposed.
2.3 FINDINGS OF LITERATURE REVIEW
1. Wentzloff, David D., and Anantha P. Chandrakasan are designed an all-digital UWB Transmitter that produce PPM pulses with a center frequency that changes to 3 channels in the 3.1-to-5GHz band without using RF oscillator. A delay-based spectral scrambling technique is designed that exploits the digital architecture. The circuit provides 47pJ/b at a data rate of 10Mb/s 1.
2. Low, Z. N., J. H. Cheong, and C. L. Law- In their paper, for UWB application, a low-cost knight’s helm shaped double-sided printed PCB antenna is designed. The antenna gives a return loss of more than 10 dB, constant group delay and gain flatness over the frequency range set by the Federal Communications Commission (FCC) for UWB application 2.
3. Yao, Jianping, Fei Zeng, and Qing Wang- Ultra wideband (UWB) that is defined by the FCC for short-range high-performance wireless communication and sensor networks with useful features, such as extremely short time delay, immunity to multipath fading, being carrier free, and having low duty cycle, wide bandwidth, and low power spectral density, has been a subject of notice recently. Furthermore, UWB signals that are generated in the optical domain can be easily tailored to have a spectrum that meets the FCC specified spectral mask. In this paper, techniques to generate UWB signals in the optical domain will be discussed. The three categories are used to define this technique for generation of UWB signals based on the following: 1) phase-modulation-to intensity modulation conversion, 2) a photonic microwave delay-line filter, and 3) optical spectral shaping and dispersion-induced frequency to- time mapping. The areas for future development and the challenge of implementation of these techniques for practical applications will also be discussed 3.
4. Wang, Hang, Lei Zhu, and Wolfgang Menzel- A novel ultra-wideband (UWB) bandpass filter (BPF) is designed. Using the hybrid microstrip and coplanar waveguide (CPW) structure, CPW nonuniform resonator or Multiple-Mode Resonator (MMR) is constructed to generate its first three resonant modes occurring around the lower end, centre, and higher end of the UWB band. 4.
5. Shaman, Hussein, and Jia-Sheng Hong- With narrow notched (rejection) band a compact ultra-wideband (UWB) bandpass filter (BPF) in the UWB passband realized on a microstrip line is implemented and presented in this paper for use in wireless communication applications within the unlicensed UWB range set by the Federal Communications Commission (FCC) 5.
6. Li, Rui, and Lei Zhu – Using stub-loaded multiple-mode resonator (MMR), a novel compact ultra-wideband (UWB) bandpass filter (BPF) is presented in this paper. The MMR is constructed by loading three open stubs in a uniform-impedance resonator, i.e., one stepped-impedance stub at the center and two uniform-impedance stubs at the symmetrical side locations 6.
7. Ru-qi Xiao, Guo Yang, Wen Wu – In this paper by the US Federal Communication Commission (FCC), the power spectral density of UWB for indoor/outdoor communication devices is defined. This paper shows the design of microstrip BPF using coupled half-wave resonators using CST microwave studio EM simulation platform 7.
8. Ishii, Hiroyuki, Toru Kimura, Naotaka Kobayashi, Atsushi Saito, Zhewang Ma, and Shigetoshi -Ohshima In this paper an ultra-wideband high-temperature superconducting bandpass filters is designed for Japan’s low-band spectrum. First, they designed a low-band filter with a microstrip three-mode resonator loaded with two open stubs. The three-mode resonator is characterized by the ease of controlling the frequency response compared with other resonators. In addition, they loaded a low-pass filter consisting of a microstrip coupled-line hairpin unit to suppress all unwanted high-frequency harmonics. The simulated filtering characteristics of the low-band filter gave a wide passband 8.
9. Zhu, Lei, Sheng Sun, and Wolfgang Menzel- Another novel microstrip line UWB band pass filter has been reported in 9 using multiple mode resonator (MMR) with insertion loss of 2 dB and group delay varies from 0.2 to 0.43 ns9.
10. Sharma, Vinay Kumar, and Mithilesh Kumar- A compact UWB band pass filter is designed using MMR with high insertion loss of 0.2 dB at center frequency of 6.8 GHz. In this letter, we present a design of microstrip ultra wideband (UWB) bandpass filter (BPF) for the use in UWB wireless communication application set by Federal Communications Commission (FCC). The UWB filter is realized with a Basic MMR (Multiple Mode Resonators) structure feed by interdigital coupled lines for achieving higher degree of coupling.
11. Azaga, Mohamed, and Masuri Othman- This paper concerns the design of microstrip BPF using coupled half-wave resonators with a pass window of 3.1 to 10.6 GHZ at a center frequency of 6.85GHz , passband insertion loss ripples 0.2 dB, minimum stopband attenuation of 20 dB on silicon substrate using IE3D EM simulation platform.
2.4 RESEARCH GAPS
In this thesis we enhance the insertion and return loss of the base paper. We improve the result and design the BPF by cascading LPF and HPF by using the Butterworth technique we design the desired filter for wireless communication. In this thesis -Ru-qi Xiao, Guo Yang, Wen Wu (Compact and High Performance UWB Band-Pass Filter based on parallel-coupled line) 7 is taken as base paper. The measured-3dB bandwidth is from 3.24 to 10.25 GHz. The insertion loss less than 1.8 dB and the return loss better than 9.1 dB can be observed over most of the UWB passband.
Fig. 2.1 Base Paper Work (Simulated and Measured Result)
Fig. 2.2 Desired Project Work
THEORY AND DESIGN
3.1.1 Filter Definition
The filter is a two-port network used to control the frequency response at certain point in a microwave system. It provides transmission at frequencies within the pass-band of the filter and attenuation in the rest of the band, the stop-band. Typical frequency responses include low-pass, high-pass, and band-pass and band-reject characteristics. The perfect filter would have infinite attenuation in the stop-band, and zero insertion loss with a linear phase response (to avoid signal distortion) in the pass-band.
3.1.2 Classification of Filters
There are four primary categories of filters which are:
Low-Pass Filter (LPF): A low-pass filter passes low frequency signals, and rejects signals at frequencies above the filter’s cutoff frequency (fc);
High-Pass Filter (HPF): The opposite of the low-pass is the high-pass filter, which rejects signals below its cutoff frequency (fc);
Band-Pass Filter (BPF): A band pass filter allows signals with a range of frequencies (fc1, fc2). ( pass band) to pass through and attenuates signals with frequencies outside this range;
Band-Stop Filter (BSF) or Band Reject Filter (BRF): A filter with effectively the opposite function of the band-pass is the band-reject or notch filter;
Fig. 3.1 Frequency Responses of the Four Types of Filters.
In this thesis bandpass filter is used and BPF is combination of HPF and LPF. Below the brief description of these filters.
3.3 HIGH PASS FILTER
A high-pass filter (HPF) is an electronics device which allows high-frequency signals through it but blocks (decreases the amplitude of) signals with frequencies lower than the cutoff frequency. The actual value of removal for each frequency changes from filter to filter. A high-pass filter is typically demonstrated as a linear time-invariant system. It is also called as a low-cut filter or bass-cut filter. High-pass filters have numerous applications, for example, blocking DC from circuitry sensitive to non-zero normal voltages or RF devices. They can also be utilized as a part of conjunction with a low-pass filter to design a bandpass filter.
The general structure of first-order high-pass filter is designed by using an input voltage across the cascaded connection of a capacitor and a resistor and placing the voltage across the resistor as a load. The multiplication of the resistance and capacitance (R×C) is known as the time constant (?); it is inversely dependent to the cutoff frequency fc, that is
Where fc is in hertz, ? is in seconds, R is in ohms, and C is in farads.
In this case, the filter has a passband gain of -R2/R1 and has a cut off frequency of
Because this filter is active, it may have non-unity passband gain. That is, high-frequency signals are inverted and amplified by R2/R1.
Fig. 3.2 An Active High-Pass Filter
From the circuit in Figure 3.2 above, according to Kirchhoff’s Laws and the definition of capacitance
Where is the charge stored in the capacitor at time . Substituting Equation (Q) into Equation (I) and then Equation (I) into Equation (V) gives:
3.4 LOW PASS FILTER
A low-pass filter is a filter that passes low frequency signals and blocks (decreases the amplitude of) signals with frequencies higher than the cut-off frequency. The real value of removal for each frequency differs relying upon specific filter design. It is also called as a high-cut filter, or treble cut filter in voice applications. A low-pass filter is the inverse of a high-pass filter. A band-pass filter is assembly of a low-pass and a high-pass filters. Low-pass filters exist in a wide range of structures, including electronic circuits, (for example, a hiss filter utilized as a part of voice), anti-aliasing filters for conditioning signals before analog to digital transformation, digital filters for smoothing sets of information, acoustic hindrances, obscuring of pictures etc. The moving normal operation utilized as a part of fields, for example, finance is a specific type of low-pass filter, and can be examined with a similar signal processing procedures as are utilized for other low-pass filters. A Low-pass filters give a conditioned signal, removing the short-term fluctuations, and leaving the longer term trend. An optical filter can effectively be known as a low-pass filter, yet ordinarily is known as a long pass filter (low frequency is long wavelength), to maintain assurance.
A general structure of low-pass filter circuit consists of a resistor connected in series with output, and a capacitor connected in parallel with the output. The capacitor shows reactance, and removes low-frequency signals, passing them through the load instead. At higher frequencies the reactance decreases, and the capacitor effectively operates as a short circuit. The assembly of resistance and capacitance gives the time constant of the filter (represented by the Greek letter tau). The break frequency, also called the turnover frequency or cut-off frequency (in hertz), is obtained by the time constant:
or equivalently (in radians per second):
To understand this circuit is to focus on the time taken by the capacitor to charge. It takes time to charge or discharge the capacitor through that resistor:
At low frequencies, there is lot of time for the capacitor to charge up to practically the same voltage as the input voltage.
The capacitor has just charge up to a little amount before the input changes the direction at high frequencies. The output reaches up and down only at a small amount for the input reaches up and down. At double the frequency, there’s only time for it to charge up half of the amount. Another way to understand this circuit is with the idea of reactance at a specific frequency:
Since capacitor blocks the DC signal and DC input must “flow out” the path represented as (analogous to open circuited the capacitor).
Since capacitor allows AC very well through it, almost as well as AC flows through solid wire .AC input “flows out” through the capacitor, effectively short circuiting to ground (analogous to changing the capacitor with just a wire).
The capacitor is not an “on/off” object (like the block or pass as explained above). The capacitor changeably acts between these two extremes. It is the Bode plot and frequency response that show this changeably.
3.5 BAND PASS FILTER
A band-pass filter is an electronic device that allows frequencies inside a specific range and blocks (attenuates) frequencies outside that range.
A bandpass filter is a device or circuit that enables signals between two particular frequencies to pass, however that rejects signals at different frequencies. Few bandpass filters need an outside source of energy and uses active elements for example, transistors and ICs; these are called as active bandpass filters. And rest bandpass filters utilize no outside source of energy and uses passive devices for example, capacitors and inductors; these are called passive bandpass filters. The amplitude versus frequency plot, additionally called a spectral graph, of the characteristics curve of a hypothetical bandpass filter. The output signal power falls to half of its level at the center frequency f0of the filter at the cutoff frequencies, f1 and f2. The f2 – f1 which is the bandwidth of the filter is expressed in hertz (Hz), kilohertz (kHz), megahertz (MHz), or gigahertz (GHz).The area between cutoff frequencies f1 and f2 is known as the filter passband.
Bandpass filters are utilized at both source and destination in wireless communication. The fundamental features of such a filter in a transmitter is to restrict the bandwidth of the response to the less important to pass on information at the required speed and in the required shape. In a receiver, a bandpass filter permits signals inside a chosen range of frequencies to be heard or decoded, while keeping signals at undesirable frequencies from overcoming. A bandpass filter also advances the SNR ratio (sensitivity) a receiver.
In both transmitting and receiving applications, having maximum bandwidth for the mode and speed of communication being used sum more signals that can be moved in a system, while limiting the noise or disputes among signals.
Fig 3.3 Band pass filter
3.5.1 Development of UWB Band pass Filters
After the release of UWB band pass filters with a pass band of the same frequency range (3.1 GHz – 10.6 GHz and a fractional bandwidth of 110%), challenges for conventional filter designs increased. Before mid-2003, the bandwidth of the pass band for a BPF was extended from 40% to 70%.
3.5.2 Microstrip multi-mode resonator with two parallel-coupled lines at two ends, it consists of a micro strip multi-mode resonator (MMR) and a parallel-coupled line at each end of the network.
The MMR has two identical high-impedance sections with a length of quarter guided wavelength at two sides and a low-impedance section with a length of half guided wavelength in the middle.
The MMR in the filter generates first and third resonant mode at the edges of the UWB pass band. The parallel-coupled lines are modified to obtain the ultra-wide pass band. This could be done by adjusting the coupling length Lc.
Fig. 3.4 The Schematic of a Micro Strip Multi-Mode Resonator (MMR) with Two Parallel Coupled Lines at Two End.
3.6 EXPRESSIONS USED IN FILTER DESIGN PROCESS
3.6.1 Scattering Parameter
The input wave a depends only on the reference impedance and the source Es, while the reflected wave b depends also on the load, and gives zero when this is matched.The reflection coefficient depends on both the circuit impedance Ziand the source impedance ZS.
Fig. 3.5 Two Port Network
The S parameters rely on both the circuit impedances and a reference impedance Z0.|a1|² and |a2|² are the incident powers at the ports 1 and 2, while |b1|² and |b2|² are the reflected powers at the two port network.
If s11 is the reflection coefficient at port 1, when a2 = 0, i.e. when the port 2 is terminated over the reference impedance.
s11 = input reflection coefficient with matched output
s12 = inverse transmission coefficient with matched output
s21 = forward transmission coefficient with matched output
s22 = output reflection coefficient with matched input
3.6.2 Insertion Loss
The loss of signal power due to the insertion of a component in a transmission line or optical fibre is defined as insertion loss and is generally defined in decibels (dB).If the power transferred to the output before insertion is PT and the power taken by the output after insertion is PR, then the insertion loss in dB is written as,
Insertion loss is taken as a ratio of the signal output in a test configuration without the filter connected (|V1|) to the signal output with the filter connected (|V2|). This ratio is defined in dB by the following equation:
Give attention that for most filters, |V2| will be smaller than |V1|. In this case, the insertion loss is positive and evaluates how much smaller the signal is after connecting the filter.
3.6.3 Reflection Loss
The loss of signal power due to returned/reflected by a break or discontinuity in a transmission line or optical fibre is known as the reflection los. This discontinuity may not be matched with the load or with a device inputted in the line. It is usually defined as a ratio in decibels (dB);
Where RL (dB) is the return loss given in dB, Pi is the incident power and Pr is the reflected power. Return loss is taken for to both standing wave ratio (SWR) and reflection coefficient (?). Maximum return loss related to minimum SWR. Return loss is a calculation of how well devices or lines are matched with load. A match is defined as good if the return loss is maximum. A maximum return loss is desirable and results in a minimum insertion loss. Return loss is applicable in recent practice in priorities to SWR because it has better resolution for small values of reflected wave.
The real definition of return loss with a plus sign is the difference in dB between the inputted power transmit towards the Device Under Test (DUT) and the power reflected back
However taking the ratio of reflected to incident power outcomes in a negative sign for return loss;
Where RL'(dB) is the negative of RL (dB).
Return loss with a plus sign is equal to the magnitude of ? when defined in decibels but of opposite sign. That is, return loss with a negative sign is generally called reflection coefficient. The S-parameter S11 from two-port network definitions is frequently also called return loss, but is actually equal to ?.
3.6.4 Q Factor
A band-pass filter may be defined by its Q-factor. The Q-factor is the inversely proportional to its fractional bandwidth. A high-Q filter will have a narrow passband and a low-Q filter will have a broad passband. These are related to the narrow-band and wide-band filters respectively.
Quality factor or Q factor is defined as a dimensionless parameter that explains how underdamped an oscillator or resonator is or similarly characterizes a resonator’s bandwidth in terms of its centre frequency. Higher Q shows a lower rate of energy loss relative to the stored energy resonator’s stored energy; the oscillations disappear more slowly. For example a pendulum suspended from a high-quality behaviour, oscillating in air, has a high Q, while a pendulum dipped in oil has a low one. Resonators with high quality factors have low damping so that they ring longer.
The width (bandwidth) of the resonance is expressed by
Where is taken as the resonant frequency, and as the bandwidth, is the width of the range of frequencies for which the energy is at least half its peak value.
The resonant frequency is often expressed in natural units (radians per second), rather than using the in hertz, as
VSWR stands for Voltage Standing Wave Ratio, and is also called as Standing Wave Ratio (SWR). VSWR is a function of the reflection coefficient, which describes the power reflected back from the filter. The VSWR is defined by the following formula, if the reflection coefficient is given by:
The reflection coefficient is also given as return loss or s11. The VSWR is always shows a real and positive value for filters. The less value of VSWR is shows the filter matched to the transmission line perfectly and the more power is delivered to the filter. The minimum VSWR is given as 1.0. In this case, no power is reflected from the filter, which is ideal case.
18.104.22.168 Physical Meaning of VSWR
VSWR is calculated from the voltage measured along a transmission line leading to a filter. VSWR is defined as the ratio of the maximum amplitude of a standing wave to the minimum amplitude of a standing wave, as seen in the following Figure:
Fig. 3.6 Voltage Measured Along a Transmission Line.
When a filter is not matched to the receiver then the power is reflected back (so that the reflection coefficient, is not zero). This gives a “reflected voltage wave”, which forms standing waves through the transmission line.
3.6.6 Group delay
Group delay is the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a device under test, and is a function of frequency for each component.3.6.7 Pass bandPass band is the band of frequencies that is allowed to pass through a filter. Pass band is equal to the frequency range for which the filter insertion loss is less than a specified value.
3.6.8 Cut-off frequencyCut-off frequency is the frequency at which the filter insertion loss is equal to 3 dB.
3.6.9 Stop bandStop band is equal to the frequency range at which the filter insertion loss is greater than a specified value. It is the band out of the pass band.
3.6.10 RippleThe flatness of the signal in the passband can be quantified by specifying the ripple or difference between maximum and minimum amplitude response in dB. Chebyshev filter response allows us to control the magnitude of the ripple.
3.6.11 BandwidthFor a bandpass filter, it is the difference between upper and lower frequencies typically recorded at the 3dB attenuation points above the passband.
Where f1 and f2 are cut off frequencies.
3.6.12 RejectionFor an ideal filter we would obtain infinite attenuation level for the undesirable signal frequencies. However, in reality we expect an upper bound due to the deployment of a finite number of filter components. Practical designs often specify 60dB as the rejection rate.
Fig. 3.7 Generic Attenuation Profile for a Bandpass Filter
METHODOLOGIES AND DESIGN PROCEDURE
4.1 DESIRED APPROACH
In this project, 5 pole BPF are used to modify and simulate the UWB BPF .The UWB BPF formed by cascading HPF and LPF is presented. The structure of BPF and the formula used to determine the design parameters have been given. Cutoff frequency for HPF is selected as 0.5Hz and cutoff frequency for LPF is selected as 6 GHz. All the structure is presented for the dual band operation.
In this project, a modified UWB BPF is developed and aim is to improve the specifications: Isolation Loss, Bandwidth and Return Loss in UWB.
In this project different simulated circuits are available with a frequency of 0.5 GHz to 6 GHz.
4.2 PROBLEM FORMULATION
Using Lumped elements Inductor (L) and Capacitor (C) HPF and LPF are formed. These filters are cascaded to form BPF. This improves the return loss and bandwidth. Using a Simple AWR simulator an idealized UWB BPF can be simulated to help determine realistic values for Return Loss and Isolation. The isolation bandwidth can be extended by an additional isolation network in the circuits. After that three circular stub MMR resonator and three arrowhead DGS structure are used to enhance the filter performance.
4.3 DESIGN METHODOLOGY
This section explains briefly about the process of designing and the software used to achieve in designing and the response desire. Before running the design, it is important to identify the flow of each process to ensure the performance of the filter design. For this project a bandpass filter is designed, then compared to the conventional and proposed. The studies were done by using Microsoft office studio to checked the filter design proposed. The overall design process was done by using CST microwave studio software. Figure.4.1 shows the overall design procedures of this bandpass filter.4.4 DESIGN SPECIFICATIONS
Software used in this project is Circuit Simulator Microwave Office2002.
1. Desired frequency = 3.1 GHz to 10.6 GHz
2. Source Impedance = 50 ohm.
3. Load Impedance = 50 ohm.
4.5 FLOWCHART OF DESIGN PROCEDURESProject background Research
& Problem Statement
Design &Simulation of filter using CST
Microwave studio Software
Performance Analysis of S-parameter, Bandwidth and Response
Final Report & Presentation
Modify filter physical
Properties and parameters
Project background Research
& Problem Statement
Design &Simulation of filter using CST
Microwave studio Software
Performance Analysis of S-parameter, Bandwidth and Response
Final Report & Presentation
Modify filter physical
Properties and parameters
Fig. 4. 1 The Flowchart of Design Procedure
4.5 EXPERIMENTAL SETUP
In this project all circuit schematic is done by Microwave Office2002 Simulator. Each Circuit has a desired S parameters response. Maximum setups are done using transmission lines. For verifications different result is analysed. It contain desired frequency and different R, L and C values with the port impedance Zo. This project contains the some Layout options for all schematic designs.
Fig. 4.2 Project Options
Fig. 4.3 Add Measurement
4.6 CALCULATION SETUP
All calculations is done using TXLINE2001- MICROSTRIP option. All desired specifications as discussed above is used from this option. Figure 4.4 shows the calculation setup.
Fig.4.4 Calculation setup using TXLINE option
4.7 THEORY OF SCHEMATIC UWB BPF
This project contain different layout and design to modify the Bandwidth, Return Loss and Isolation loss. In this chapter all the schematic of UWB BPF are modified .Their results and graph analysis is shown in chapter 5.
RESULT AND DISCUSSION
In this chapter, the analysis of UWB BPF Design is explained. Finally, the results obtained from the simulations are demonstrated.
5.2 DESIRED SPECIFICATIONS
The essential parameters for the design of a UWB BPF are:
•Frequency of operation (fo): The cutoff frequency of the HPF and LPF must be selected appropriately. The cut off frequency selected for my design for HPF is 0.5 GHz and for LPF is 6 GHz.
• INDUCTOR, CAPACITOR, Zo =50 ohm (characteristic impedance)
5.3 SIMULATION SETUP
The software used to model and simulate UWB BPF is CST Microwave Studio 2011 and Microwave office2002 software. CST Microwave Studio 2011 and Microwave Office is a full-wave electromagnetic simulator. This is the Computer Simulation Technologies software and AWR (Applied Wave Research) software for designing Microwave Integrated Circuits It analyses 3D and multilayer structures of general shapes of Microstrip Line. It has been widely used in the design of MICs, RFICs, patch antennas, wire antennas, and other RF/wireless antennas. This software may also use to measure and plot the S11 parameters, VSWR, bandwidth, return loss as well as the group delay. An advanced version of the software was used to obtain the results for this thesis.
5.4 GRAPHICAL ANALYSIS
In the last chapter we have seen the schematic circuits of UWB BPF. Their analysis is given below. Final and the best result is given in the last. From the graph return loss, Isolation Loss as well as Bandwidth has been calculated.
5.5 CIRCUITS AND THEIR GRAPHS
5.5.1 Analysis and Comparison of 5 Pole Simply Designed BPF and 5 Pole BPF Design by Cascading HPF and LPF
Analysis of 5 Pole BPF Design by Cascading HPF and LPF
Fig. 5.1 Schematic of UWB BPF using Lumped elements
TABLE 1: 5 Pole BPF elements
ELEMENT NO. HIGH PASS FILTER LOW PASS FILTER
1. L1=9.836 C1=10.306 L1=0.8196 C1=0.8583
2. L2=9.836 C2=9.836 L2=2.6525 C2=0.8583
3. C4=10.306 L3=0.8196
Fig.5.2 Simulated Graph Showing Insertion Loss S21and Return Loss s11 for Cascaded BPF
22.214.171.124 Analysis of 5 pole simply designed BPF
Fig. 5.3 Schematic of UWB BPF Using Lumped Elements
Fig. 5.4 Simulated Graph Showing Insertion Loss S21and Return Loss s11 for Simple BPF
From above graphs it is clear that the cascaded BPF gives better result than the simple BPF.
5.6 INTRODUCTION OF DGS FOR ENHANCEMENT OF PERFORMANCE
Achieving the best power profile, and the lowest insertion loss, designers develop a new method and structure to overcome on the limitations of lumped-element. Introducing Defected ground structure (DGS) technique is one of the key solutions to achieve the best performances.
Proposed filter is designed on the FR4 substrate with the size of 20 mm × 20 mm with the dielectric constant of 4.3 and substrate height is 1 mm. The proposed filter have three arrow head defected ground structure (DGS) which enhance the pass band as well as roll off factor as depicted in figure 5.5.
Fig. 5.5 DGS Structure with Three Arrowhead Shape
The schematic studied of the proposed filter represents a BPF for ultra-wideband (UWB) applications based on multiple-mode resonator (MMR) using interdigital feed lines structure combined with defected ground rectangular structure (DGS), aiming to transmit the signal in the whole UWB pass band of (3.1 – 10.6 GHz). It is designed on a substrate with a relative dielectric constant of ?r = 4.3 and a thickness of h=1 mm.The use of parallel coupled feed lines is able to enhance the coupling degree between the feed lines. This coupling can be adjusted to control the bandwidth. Accordingly, the symmetrical parallel coupled feed lines can work together to keep he UWB-BPF in the desired range. The input and output ports are designed to ??of 50 ?.
5.7 Proposed wide band bandpass filter Result Discussion
There are three circular stubs on the top of the substrate with microstrip coupled line which is enhancing the other desired parameters like return loss, insertion loss, group delay etc. of the proposed filter. All dimensions of the proposed UWB BPF filter is also defined under the figure 5.6.
L=20 mm, W= 20 mm, Ls =5mm, Lt = 2mm, R =0.7 mm, Wt=2mm
Fig. 5.6 Proposed MMR Based UWB Filter structure
The parametric analysis of proposed filter has been carried out using CST Microwave Studio Tool. All the parameters of the filter are analysed at three different radiuses of side stubs which is denoted by R.
The parametric study of simulated results of return loss of the proposed filter is shown in figure 5.7.On the variation of R with0.5 mm; the minimum suppression is -42 dB have been noticed with the frequency range of 3.59 – 10.97 GHz. Further increases the radius to a value of 0.6 mm value of minimum suppression is further decreases to a value of -51 dB with frequency range of 3.59- 10.7 GHz. At the value of radius 0.7 and 0.8 mm minimum suppression and frequency
range are -61 dB, -42 dB, 3.6-10.45 GHz and 3.6- 10 GHz respectively. From above these we can analyse the low as low value of minimum suppression is achieved at radius of 0.7 mm whereas somehow compromise in terms of frequency range. Return loss in pass band is -61 dB so this mean only about 0.001% power is reflected back in pass band which is very less . Return loss in stop band is about -0.25 dB so this means about 90% power is reflected back in stop band from port -1 to port-2.
Fig. 5.7 Return loss analysis in Pass band
Fig. 5.8 Pass band results of proposed UWB filter
All these radiuses of side stubs. The insertion loss is about -0.2 dB and same for these entire changes in the radius with fractional bandwidth 111% as shown in figure 5.8. Insertion Loss in pass band is about -0.2 dB so this means about 90% power is transmitted in port 1 to port 2. Insertion loss in stop band is about -45 dB so this means about 0.01% power is transmitted in port 1 to port 2. The filter is featured by good performance in stop band. The defected ground structure (DGS) with three arrowhead is improve the pass band response of the proposed filter and also use to size miniaturization and reconfigurability.
Here, the simulated graph of S parameters , VSWR, group delay, eye diagram and magnetic field of proposed filter at 0.7 mm radius on CST microwave studio is presented an studied. In figure 5.9 the Simulated Graph showing Insertion loss S21and return loss s11 for wide band BPF.
Fig. 5.9 Simulated Graph of Insertion loss S21and return loss s11 for wide band BPF on CST Microwave studio
For the best performance of filter the VSWR value must remain below 2.From the figure 5.10 it is clear that the filter show good VSWR value which is 1.1326.
Fig 5.10 Simulated Graph showing VSWR for Ultra Wide Band BPF on CST Microwave Studio
The group delay must be linear and constant for better performance and stability of the filter. The group delay of the proposed filter is more constant with a variation less than 0.1 ns at the interested frequency range as shown in figure 5.11, so that’s mean this filter has good stability.
Fig. 5.11 Simulated Graph showing group delay for ultra wide band BPF on CST Microwave studio
In the eye diagram shown in figure 5.12, the trise and tfall both are 0.1 ns. For the best performance eye diagram must be below than 0.2 ns for both.
Fig. 5.12 Simulated Graph showing Eye diagram for Ultra Wide Band BPF on CST Microwave studio
Magnetic field distribution gives a general idea about the filter selectivity, if it is really a BPF or not, and defines the effective parts of the filter.
Figure 5.13 shows that the maximum power is situated in the interdigital feed lines, where it can be modified to apply any optimization into the filter performances.
Fig. 5.13 Simulated Graph showing Magnetic field for Ultra Wide Band BPF on CST Microwave Studio
5.8 Result Summery
The overall result summery of microstrip UWB BPF is given in table below.
S11(dB) S21(dB) 3dB bandwidth
(GHz) Tg (group delay) in nsec VSWR Size (mm × mm) Application
-50 0 to -0.5 6.972 0.2 1.15 20 × 20 WLAN, Mobile Communication, WiMAX Technology
Substrate height(mm)h Conductor thickness(?m) Permittivity (?r) Conductor Conductance(S) Connector Type Fractional BW in %
1 35 FR-4 (4.3) Copper 5.2×107 SMA 111
Table 2. Overall Result Summery
5.9 Result Discussion:
Calculation of % B.W : ( F2-F1)*100/f0=(10.6-3.7)*100/6.97=111%
VSWR=1.15 it gives the reflection coefficient value=0.06 which is very less so most of the power is transmitted from port 1 to port 2.
Reflection coefficient = (VSWR-1)/ (VSWR+1) =0.06
Return loss in pass band is -62dB so this mean only about 0.001% power is reflected back in pass band which is very less.
Return loss in stop band is about -0.25dB so this means about 90% power is reflected back in stop band from port -1 to port-2.
Insertion Loss in pass band is about -0.2dB so this means about 90% power is transmitted in port 1 to port 2.
Insertion loss in stop band is about -45dB so this means about 0.01% power is transmitted in port 1 to port 2.
Group delay is almost constant in pass band and variation of group delay in pass band is ;0.1nsec.so that’s mean this filter has good stability.
Size of this filters is very compact its dimension is 20×20 mm.
Eye diagram shows rise time and fall time is 1nsec and amplitude is 0.2 which is highly synchronized.
CONCLUSION & FUTURE WORK
In this thesis, a UWB filter with wideband characteristics has been designed and analyzed using CST microwave studio tool. The MMR techniques is not only offer low insertion loss as well as better matching with transmission line. This filter is composed of three circular stubs. The performance of the filter is best at radius 0.7mm out of other radiuses. It shows the frequency range 3.6-10.45 GHz (Bandwidth-6.85 GHz) with minimum suppression of -62 dB, which is comes under the UWB range defined by FCC. By adding the short- and open-circuited stubs at input/output ports for impedance matching, the performance of the filter can be improved further. The three arrowhead defected ground structure (DGS) is also enhancing the performance of the filter. The DGS is used to miniaturize the size of filter. Therefore good pass band behavior and compact structure of proposed filter is best suitable for recent mobile communication technologies.
UWB BPF microstrip filters play pivotal roles in wireless or mobile communication systems. In this way, we have studied and designed an UWB BPF with a new concept providing efficiency and good performances which is Defected Ground structure.
Our work shows a compact Bandpass Filter (BPF) using DGS for Ultra-Wideband (UWB) Systems. The proposed BPF consists of circular stub MMR structure at the top and the arrowhead shaped DGS at the bottom of the substrate.
This contribution highlights the main role of a Defected Ground Structure in a filter design, which is the maintain of the return loss in a highest level, offers improved performances, and reduces the whole filter size.
In summary, we have designed a tuned UWB BPF structure which satisfied all requirements of lowest insertion loss, highest return loss, high rejection and compact size, also, the simulation results are in satisfactory agreement with the FCC regulations.
The filter proposed in this thesis will be modified and optimized as follow:
The minimization of the total size of this filter;
The creation of a new DGS design;
Modelling this UWB BPF
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LIST OF PUBLICATIONS
Published paper on IJREAM titled as “Design of Compact DGS Shaped Microstrip UWB Bandpass Filter Based on Circular Stub MMR for Mobile Communication” has been published in Volume 04 Issue 02, May 2018.
Published paper on ICTACT titled as “A Review Paper on Overview of Worldwide Interoperability for Microwave Access (WiMAX) innovation and its future utilizations” has been published in Volume 9 Issue 2, June 2018.
SAVITA YADAVEmail: [email protected]
Mobile: +91- 955597507125590522605900
Pursuing M. Tech (ECE) from AKTU and scored 79.8 % till third semester.
Secured Bachelor of Technology Degree in ECE from the Uttar Pradesh technical University with 72.93% in the year 2013.
Intermediate: Completed 10+2 from GIC, Shaktinagar from U.P. BOARD with 70% in the year 2008.
High School: Completed 10th from GIC, Shaktinagar from U.P. BOARD with 73.10 % in the year 2006.
Personal Details: Name : Savita Yadav
Father’s Name : Late Mr Rama Shankar Yadav
Mother’s Name : Mrs Saraswati Devi
Date of Birth : 02-12-1989
Nationality : Indian
Languages Known : English, Hindi
I declare that the given details are true and correct to the best of my knowledge.
Date: June 12, 2018 (Savita Yadav)