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Analysis and Design of Microwave Reconfigurable Filters in Esiw Technology

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Analysis and Design of Microwave Reconfigurable Filters in Esiw Technology FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT ANALYSIS AND DESIGN OF MICROWAVE RECONFIGURABLE FILTERS IN ESIW TECHNOLOGY Mar´ıa Trinidad Julia´ Morte 910411-T308 Juan Rafael Sanchez´ Mar´ın 911111-T275 September 2015 Master’s Thesis in Electronics “After climbing a great hill, one only finds that there are many more hills to climb.” Nelson Mandela To my brother, wherever you are you will be always proud of me. JR Acknowledgement We would like to thank to our supervisor Prof. Carmen Bachiller for the continuous sup- port of our Master’s Thesis and related research, for her patience, motivation, and immense knowledge. Her guidance helped us in all the time of research and writing of this thesis. We could not have imagined having a better supervisor. Furthermore, we reserve our biggest thanks to our families for encouraging us in our experience in Gavle.¨ They have been always supporting us throughout writing this thesis and in our life in general. Juanra and Mar´ıa Abstract Microwave filters are essential components in high frequency communication systems. The features required for these devices are increasing due to the increase in frequency, caused by the saturation of the electromagnetic spectrum. Among these features, the need for low cost devices with a reduced mass and volume and the need to integrate them with the current planar technology are highlighted. In addition, it is interested to have reconfigurable devices, that is, they can adjust their frequency response, replacing the need of multiple devices. So far, metallic waveguide filters have been used, but lately Substrate Intregated Waveguide (SIW) technology has appeared, and within this family, the innovative Empty Substrate Integrated Waveguide (ESIW). ESIW technology is empty, so that, it can be filled with liquid crystal (LC). The LC is a dielectric material with variable permittivity, which makes the filter can change its center frequency and bandwidth. There are several commercial tools based on numerical methods that enable to carry out the analysis and design of these structures, but they require a very high computational time during the analysis process. This affects negatively the automated design of these structures. On the one hand, an efficient and accurate analysis tool is developed in the thesis by fol- lowing a strategy that consists on dividing the device under analysis in simple building blocks: waveguides filled with dielectric material, change of medium, discontinuities between guides and dielectric discontinuities. All of them are canonical structures or sufficiently simple that can be analyzed with modal methods. The Generalized Scattering Matrix (GSM) of each block is obtained, and they are linked in cascade by using an efficient technique. The accuracy and effectiveness of this tool are checked using it to analyze multiple filters, comparing the result with a commercial software. Furthermore, an analysis about how the variation of the permittivity of the liquid crystal affects in the frequency response of the filter is made. On the other hand, a tool for designing filters for high frequency communications is de- veloped, in order to integrate it into a Computer Aided Design (CAD) tool. To do this, the classical techniques for designing waveguide filters are followed by adapting them to the new topology under design. Different synthesis and optimization strategies are implemented. These strategies are based on the synthesis of a starting point, the segmentation of the struc- ture under design and the hybridization of different optimization algorithms. Also, a tool for calculating the values of the permittivity of the LC that allows the recon- figuration of the filter is developed. These new permittivities enable to obtain a new desired frequency response. VIII This tool has been used to design various microwave filters on H plane, using ESIW technology filled with liquid crystal. The accuracy and the effectiveness of this tool are checked. In addition, the reconfiguration tool designed is evaluated. Finally, a study of the manufacturing aspects is done, such as how to feed the filter and the solutions to polarize the liquid crystal. Taking into account all these considerations a prototype is manufactured and measured. Index Abstract . VII List of figures XI List of tables XV 1 Introduction 1 1.1 Motivation and aims . .1 1.2 Structure of the thesis . .2 1.3 State of the Art . .4 1.3.1 Microwave filters . .4 1.3.2 Reconfigurable filters . .7 1.3.3 ESIW technology . .8 2 Analysis of reconfigurable filters 11 2.1 Analysis methods for waveguide filters . 11 2.1.1 Modal methods . 12 2.1.2 Numerical methods . 12 2.1.3 Hybrid methods . 13 2.2 Analysis methodology of reconfigurable filters . 13 2.2.1 Analysis method of the change of medium . 15 2.2.2 Analysis method of multiple discontinuities . 18 2.2.3 Analysis method of steps between waveguides . 24 2.2.4 Generalized Scattering Matrices connection method . 26 2.3 Validation of the analysis tool . 28 2.3.1 Filter analysis . 28 2.3.2 Permittivity variation of the liquid crystal . 31 3 Design of reconfigurable filters 43 3.1 Specifications . 45 3.2 Synthesis . 45 3.2.1 Lowpass prototype . 46 3.2.2 Scaling and frequency conversion . 48 3.2.3 Implementation of the filter . 50 X Index 3.3 Optimization . 53 3.3.1 Error function . 54 3.3.2 Optimization strategies . 55 3.3.3 Optimization strategy used . 63 3.4 Validation of the design tool . 64 3.4.1 Two cavities filter . 66 3.4.2 Four cavities filter . 68 3.5 Reconfiguration . 71 3.6 Validation of the reconfiguration tool . 73 3.6.1 Two cavities filter . 73 3.6.2 Four cavities filter . 75 4 Technological aspects of manufacturing 83 4.1 Filter feed . 83 4.2 Liquid crystal and its microwave applications . 87 4.2.1 Liquid crystal properties . 89 4.2.2 Liquid crystal encapsulation . 89 4.2.3 Liquid crystal polarization . 90 4.3 Choke Inductor . 92 5 Results and measurements 95 5.1 Redesign of the filter . 95 5.2 Manufacturing process . 100 5.3 Measurements . 108 6 Conclusions and future research lines 113 A Calculation of the Z matrices of multiple discontinuities 117 B Resolution of the connection method for Generalized Scattering Matrices (GSM)121 C Routines 125 C.1 Analysis routines . 125 C.2 Design routines . 129 List of Figures 1.1 ESIW filter filled with liquid crystal. .2 1.2 Coupled cavities H-plane filter. .5 1.3 Coupled cavities filter with dielectric resonators posts. .5 1.4 SIW scheme. .8 1.5 ESIW layout. .9 2.1 N cavities filter filled with dielectric material. 11 2.2 Filter sections for analysis. 14 2.3 Change of medium and reference system. 15 2.4 Multiple discontinuities and reference system. 18 2.5 Detail of the current waves in the structure. 20 2.6 Specific case for three discontinuities. 22 2.7 Multiple discontinuities with voltage waves. 23 2.8 Section step analyzed with Mode Matching. 25 2.9 Cascade connection of N dispersion matrices with the new method. 27 2.10 CST configuration to simulate the filter. 29 2.11 Frequency response of the 2 cavities filter. (a)S11. (b)S21............ 30 2.12 Frequency response of the 4 cavities filter. (a)S11. (b)S21............ 31 2.13 Frequency response of the two cavities filter for case 1. 32 2.14 Frequency response of the two cavities filter for case 2. 33 2.15 Frequency response of the two cavities filter for case 3. 34 2.16 Frequency response of the two cavities filter for case 4. 35 2.17 Frequency response of the two cavities filter for case 5. 36 2.18 Frequency response of the two cavities filter for case 6. 37 2.19 Frequency response of the four cavities filter for case 1. 37 2.20 Frequency response of the four cavities filter for case 2. 38 2.21 Frequency response of the four cavities filter for case 3. 38 2.22 Frequency response of the four cavities filter for case 4. 39 2.23 Frequency response of the four cavities filter for case 5. 39 2.24 Frequency response of the four cavities filter for case 6. 40 2.25 Frequency response of the four cavities filter for case 7. 40 2.26 Frequency response of the four cavities filter for case 8. 41 2.27 Frequency response of the four cavities filter for case 9. 41 XII LIST OF FIGURES 3.1 Design flow of a computer-aided design. 44 3.2 Synthesis process flow. 45 3.3 Chebyshev ideal response. (a) Two cavities. (b) Four cavities. 46 3.4 Lowpass normalized prototype. (a) Prototype starting with a shunt element. (b) Prototype starting with a series element. 47 3.5 Low-pass to bandpass prototype transformation. (a) Transformation of series inductive element. (b) Transformation of shunt capacitive element. 49 3.6 Filter scheme using impedance inverters. 50 3.7 Waveguide filter filled with dielectric. 51 3.8 Analyzed section for the calculation of the coupling window width. 52 3.9 Formation of the initial simplex. 58 3.10 Ideal Chebyshev response. (a) Two cavities. (b) Four cavities. 65 3.11 Two cavities prototype. 66 3.12 Frequency response of the 2 cavities filter. (a) S11. (b) S21........... 69 3.13 Four cavities prototype. 70 3.14 Frequency response of the 4 cavities filter. (a) S11. (b) S21........... 71 3.15 Frequency response of a filter of two cavities centered at 11.3 GHz. 74 3.16 Frequency response of a filter of two cavities centered at 11.2 GHz. 75 3.17 Frequency response of a filter of two cavities centered at 11.1 GHz.
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