Design and Optimization of Five Pole Coaxial Microwave Bandpass Filter 

Frequency Characteristics of DGS Unit

  We achieve a DGS element by etching a defect process from the ground plane of a microstrip line. It can obtain a simple or sophisticated geometry defect form. Defect ground structures perturb the shielded current distribution in the ground plane [6,4]. This inconvenience changes characteristics of microstrip line such as its capacitance and inductance to obtain slow-wave effect and stopband in some frequency ranges [9]. A DGS element acts as an equivalent parallel RLC or LC resonant circuit connected in series with transmission lines at both of their ends [4]. Generally, the DGS can give both slow wave propagation in the passband and better attenuation properties in the stopband [3]. In this thesis, we dealt with two DGS unit shapes and compare their characteristics. Moreover, the elements are used in lowpass filter synthesis and the obtained performances are analyzed.

DGS Frequency Features

   The EM simulation is the essential resourcefulness to design and analyze DGS. Figure 2.2 presents the etched element form of the Double Triangle-Head DGS (DTH DGS) section, which is situated on the bottom metallic ground plane of a microstrip line. To examine the frequency features of this DGS unit. The figure 2.3 presents the DGS unit section which can give cut-off frequency and attenuation pole in some frequencies.
EM simulation of the single DGS is illustrated in figure 2.3:
 A 3dB cutoff frequency of 3.1GHz
 An anti-resonant frequency (Zero Transmission TZ) of 8.57 GHz.
 Just one anti-resonant pole is observed at 8.57 GHz, namely that the inductance and capacitance due to the DGS dimensions are unique over the frequencies.
 Concerning the performance bands from 1.0 GHz to 8.5GHz, the DGS presents the same S-parameter characteristics as a Butterworth type Lowpass filter (order one N=1) designed to have the same cutoff frequency of 3.1 GHz. The results of simulation illustrate that one-pole lowpass filter characteristics. The use of the DGS unit operating at less than its pole frequency increases the effective inductance of a microstrip line. The cutoff frequency is fundamentally related on the etched slot head zone in the ground plane. In addition, the attenuation pole position is thanks to the width slot etch. In fact, it is noted that a zero transmission can be extracted by making a combination of the inductance and capacitance components. Therefore, the DGS unit is entirely demonstrated by the etched slot width, length and head area in case of slots with certain head shape.

General Formulation of Aggressive Space Mapping (ASM) Optimization Algorithm

   Space mapping (SM) is a technique widely used for the design and optimization of microwave filter components [29-30]. The SM algorithm assumes the existence of two simulation tools of different accuracy and efficiency, one is more precise but more complex and CPU intensive model, namely the fine model; two is simple and computationally efficient, although not accurate model, namely the coarse model. The theory of Space Mapping is to use a coarse model to find optimization results, and then use a fine model to test the results. During this process, if the error after the testing in the fine model was over a certain tolerance, the error returns to the coarse model for another re-optimization is performed to gain a new result. The new result would be resend to fine model for testing. Space Mapping repeats these steps until the error is lower than a user define. The Aggressive Space Mapping technique has been considered in [30]. The ASM algorithm is an improvement of the original SM previously mentioned because Quasi-Newton iteration is introduced using the classical Broyden formula [31]. Here, the coarse model is the equivalent circuit shown in Figure 3.23 and the fine model is the physical model.

Principles and classification of antennas

   An antenna is an electromagnetic transducer, used to convert, in the transmitting mode, guided waves within transmission lines to radiate free-space waves, or to convert, in the receiving mode, free-space waves to guided waves. Most fundamentally, an antenna is a way of converting the guided waves present in a waveguide, feeder cable or transmission line into radiating waves travelling in free space, or vice versa. Figure 4.1 shows how the fields trapped in the transmission line travel in one dimension towards the antenna, which converts them into radiating waves, carrying power away from the transmitter in three dimensions into free space [18].The art of antenna design is to ensure this process takes place as efficiently as possible,with the antenna radiating as much power from the transmitter into useful directions, particularly the direction of the intended receiver, as can practically be achieved [18]. The equivalent circuit of an antenna is given in Figure 4.2. as one can see that there is an impedance (Zg) at the generator. The characteristic impedance of the transmission line (Zc) which does not depend on the length of the transmission line but depends upon the material used in the transmission line and the impedance matching.

Proximity Coupling

   In this feeding technique, the coupling of the patch and the feed line is obtained by placing the patch and the feed at different substrate levels as shown in Figure (4.13). A thin layer of high dielectric constant substrate is used to reduce the radiation from the feed lines,where as a thick layer of low dielectric constant substrate is used in the upper layer to increase the radiation of the patch [3]. The main advantage of this feed technique is that it eliminates spurious feed radiation and provides very high bandwidth (as high as 13%), due to overall increase in the thickness of the microstrip patch antenna. Matching can be achieved by controlling the length of the feed line and the width-toline ratio of the patch. The major disadvantage of this feed scheme is that it is difficult to fabricate because of the two dielectric layers which need proper alignment. Also, there is an increase in the overall thickness of the antenna.

Table des matières

Dedication II
Acknowledgement III
Abstract III
List of Figures III
List of Tables III
List of Abbreviations III
General Introduction
Chapter One: An Overview of Microwave Bandpass Filter Theory 
1.1 Introduction 
1.2 Filters Approximation 
1.2.1 Butterworth Function Approximation
1.2.2 Chebyshev Function Approximation
1.2.3 Elliptic Function Approximation
1.3 Elements Realization for Lowpass Prototype Filters 
1.3.1 Butterworth Lowpass Prototype Filters
1.3.2 Chebyshev Lowpass Prototype Filters
1.3.3 Elliptic Lowpass Prototype Filters
1.4 Lowpass Prototype to Bandpass Filter Transformation 
1.4.1 Lowpass Prototype Filter with ideal J and K inverters
1.5 Extraction Circuit Models for Chebyshev Bandpass Filters 
1.6 Influences of losses on bandpass filters 
1.7 Conclusion 
Chapter Two: Defected ground structure (DGS) Technique 
2.1 Introduction 
2.2 Defected Ground Structure Element 
2.3 Frequency Characteristics of DGS Unit 
2.4 Analysis and Design of the DGS 
2.4.1 DGS Frequency Features
2.4.2 Circuit Equivalent Modeling and Parameter Diagnostic
a. Circuit Modeling: Parallel LC
b. Circuit Modeling: Parallel RLC
2.5 Various DGS slots Topologies Modeling 
2.5.1 Study of Double Triangular-Head DGS (DTH-DGS)
a. Effect of Slot Head Dimension (a=b)
b. Effect of Slot Width (g)
c. Effect of the slot length (d)
2.5.2 Study of Triangular-Head-DGS (TH-DGS)
a. Effect of Slot Head Dimension (a=b)
b. Effect of Slot Width (g)
c. Effect of the slot length (d)
2.6 Design of proposed Quasi-Elliptic Lowpass Filter with single attenuation pole 
2.6.1 Conception of typical Hi-LO Lowpass Filter (LPF)
2.6.2 Propose of Quasi-Elliptic Lowpass Filter based semicircular- DGS
2.7 Conclusion 
References
Chapter Three: Microwave Filter Optimization: Polynomial and Coupling Matrix 
3.1 Introduction 
3.2 Basic Equations for Polynomials Function for Filter Networks 
3.2.1 Transmission and Reflection Polynomial Synthesis
3.2.2 Normalization of the transfer function and characteristic polynomials
3.2.3 Characteristic and properties of the design polynomials
3.2.4 Polynomial synthesis for Symmetric and Asymmetric Filtering Functions examples
3.3 Generalized Chebyshev Polynomials Approximation (Pseudo Elliptic) 
3.3.1 Polynomial Synthesis
3.3.2 Recursive Cameron Algorithm
3.3.3 Recursive Algorithm Implementation by Matlab
3.4 Coupling Matrix Synthesis of Microwave Filters 
3.4.1 Coupling Matrix Definition
3.4.2 Impedance Matrix Calculation
3.4.3 The Formulation General of the Coupling Matrix CM
3.5 Synthesis process of the (N +2) Transversal Coupling Matrix 
3.5.1 Basics for (N x N) Coupling Matrix Synthesis
3.5.2 (N+2) Transversal Coupling Matrix Representation
a. Calculation of Admittance Function [Y]-Parameters
b. Circuit Approach: Transversal Microwave Filter Network
c. Construction of Transversal Coupling Matrix (TCM)
d. Reduction of Transversal Coupling Matrix to the Folded Canonical Form
3.6 Illustrative examples and discussions 
3.6.1 Illustrative Example I: Simulated fifth-Order Filter with Four TZs
3.6.2 Illustrative Example II: Diagnosis of a Fourth-Order Filter with one TZ-
3.7 Computer–Aided Tuning and Diagnosis Techniques of Microwave Filters 
3.7.1 Bandpass Filter Modeling and Synthesis
3.7.2 Generalized Formulation of Cauchy Method for Parameter Extraction (PE)
3.7.3 General Formulation of Aggressive Space Mapping (ASM) Optimization Algorithm
3.8 Design and Optimization of Five Pole Coaxial Microwave Bandpass Filter 
3.8.1 Design Coaxial Filter Using the Coupling Matrix Model
3.8.2 Physical Realization of Coupling Matrix
a. Calculation of Resonance Frequency of Coaxial Resonator Cavity Configuration
b. Calculation of wall Dimensions for Inter-resonator Coupling
c. External Quality Factor (Qext) Calculation
3.8.3 Hybrid Optimization Using the Cauchy and ASM techniques
a. Dimensioning problem for coaxial microwave filter Design
b. Proposed Solution Using the Combinations of Cauchy/ ASM Techniques
3.9 Conclusion 
References
Chapter Four: Substrate Integrated Waveguide Antennas 
4.1 Introduction 
4.2 Principles and Classification of Antennas 
4.3 Micro strip Antenna 
4.4 Waves in Microstrip 
4.4.1 Surface Waves
4.4.2 Leakey Waves
4.4.3 Guided Waves
4.5 Basic Characteristics 
4.6 Feeding Methods 
4.6.1 Microstrip Line
4.6.2 Co-axial Probe
4.6.3 Aperture Coupling
4.6.4 Proximity Coupling
4.7 Methods of Analysis 
4.7.1 Transmission line model
a. Effective Length, Resonant Frequency, and Effective Width
b. Conductance Resonant, Input Resistance and Matching Techniques
4.7.2 Cavity model
4.8 Substrate Integrated Waveguides 
4.8.1 SIW design rules
4.8.2 Guided wave and Leaky wave Regions of Operation
4.8.3 Circular Substrate Integrated Waveguide Cavity
4.9 Neural Network Algorithm 
4.9.1 Feed-forward (Input Signal)
4.9.2 Back Propagation (Output Error)
4.10 Results and discussion 
4.10.1 Simulation Software
4.10.2 Proposed antennas geometry and design procedures
4.10.3 Artificial neural network modeling of SIW antenna
a. Results and discussion of circular SIW antenna (microstrip-to-SIW transition)
a.1 Data generation
a.2 Network architecture and training
a.3 Optimization results
b. Results and discussion of SIW antenna (coax-to-SIW transition)
b.1 Design and data generation
b.2 Network architecture and training
b.3 Optimization Procedure
b.4 Simulated Return Losses
b.5 Input Impedance and Radiation Pattern
b.6 Equivalent Circuit Model
4.11 Conclusion 
References
General Conclusion
List of publications

Télécharger le rapport complet