Study On High Performance Microwave Filters

With the rapid development of wireless communication and mobile communication technology, miniaturization, integration, multi-functional, low-cost andreliability are required for modern microwave and millimeter wave systems. It brings great challenges for the engineers to design miniaturized filters with high performance quickly and efficiently, as filters is an important part of the system. How to design miniaturized filters with high performance is studied in this dissertation from several perspectives, including the design method, the resonator structure, design technology and materials. This dissertation can be divided into two parts. The first part focuses on the microwave filter theory. The basic theory and design method of the filters are discussed, which is the basis for the design of microwave filters. Improved knowledge embedded space mapping optimization algorithm is proposed, which can help to design filters quickly and efficiently. Dual mode microstrip resonators are studied. After modeling and analyzing dual mode filters, dual mode filters with general chebyshev response and minimized size can be acheived. The second part is about the microwave filter design examples. Ultra-wideband (UWB:3.1GHz-10.6GHz) filter series and a ka-band triplexer are designed and fabricated using low temperature co-fired ceramic (LTCC) technology based on the filter theory and design methods. An S-band high temperature superconductor (HTS) filter and an X-band HTS filter are designed and fabricated with HTS technology.The major contents and contributions of this dissertation can be outlined as follows:1. Improved knowledge embedded space mapping technology is proposed to design the substrate integrated waveguide (SIW) filters. Extracted design curves are first used as the embedded knowledge in space mapping algorithm, to solve the problem of mismatch of parameters of the course model and fine model. Base on the proposed optimization algorithm, we can design SIW filters quickly and effectively.2. The dual mode resonator is analyzed and the coupling characteristic is determined. A method to realize filters with folded canonical form is proposed based on the dual mode resonators. We can get different coupling characteristic of the two modes when the disturbance is placed in different place of the dual mode resonator. On this basis, we can realize filters with folded canonical form, which means that general chebyshev filters can be realized using dual mode resonators, such as filters with multiple transmission zeros, filters with linear phase.3. A series of miniaturized UWB filters have been developed based on LTCC technology. A multi-mode resonator is proposed to realize UWB filter with transmission zeros to improve the frequency selectivity. A multi-mode resonator with inherent zeros is proposed to realize the UWB filter with a notched band to eliminate the unwanted signals in UWB band. By coupling a couple of1/4λ transmission lines to a UWB filter, a UWB filter with a stopband can be realized to suppress the WLAN signals.4. Novel LTCC triplexer with star-junctionin Ka-band has been developed. Based on LTCC multilayer technology, vertical coupling structure is adopted in three filter channels in order to achieve miniaturization. And then, the three filter channels are coupled to a common resonator to realize the absorptive network.5. HTS filters with extremely low insersion loss and high rejection in S-band and X-band have been developed. The T1-2212superconducting thin films were prepared on both sides of the substrate of LaAlO3(001). An S-band10-pole HTS filter and an X-band6-pole HTS are designed and fabricated. HTS filters show the advantage of low insertion loss, small size and high selectivity.