The Study Of Theory And Key Technology For Generalized Chebyshev Filters And Waveguide Diplexers

Filters and diplexers are important components for channel selection and signal separation in modern microwave and millimeter-wave systems. Their electrical performances are crucial for communication systems. The key requirements for filters and diplexers include low insertion loss, compact size, sharp frequency selectivity, low costs and quick design simultaneously. Traditional filtering functions and design methods can no longer keep up with the paces of microwave and millimeter-wave technique development.The generalized chebyshev filters have skirt selectivity, flatten the group delay and can be used to generate multiple-band filters. The attractive characteristics make them very popular in the microwave and millimeter-wave system. The filters have flexible design but are very difficult to simulate and optimize. Several numerical algorithms are applied to model the generalized chebyshev filters and diplexers by domestic and foreign researchers based on full-wave analysis. Designers pay much attention to the mode matching method because of its features of high precision and fast simulation speed in passive component design. Four-port network with partial height cylindrical objects in rectangular waveguide junctions (i.e., Four-port rectangular junctions), multiple-stepped rectangular waveguide bend and T-septum rectangular waveguide junction are modeled by full-wave mode matching method in order to quickly design the combline cross-coupled filter, corner waveguide diplexer, generalized chebysheve waveguide filters and diplexers with high efficiency in this paper. Substrate integrated waveguide (SIW) technique is widely applied to design the microwave and millimeter-wave devices. It is constructed by the metallized via holes on the substrate. This technique features low costs, compact size and is easily to be integrated with planar circuits.The purpose of this paper is to extract the coupling matrix of generalized chebyshev filter, model the four-port rectangular junctions, multiple-stepped rectangular waveguide bend and T-septum rectangular waveguide junction by full-wave methods and design generalized chebyshev filters and diplexers. The main works are as follows:1. Systematically research on the theory of generalized chebyshev filtersThe generalized chebyshev filters are based on the all-coupled model. The coupling matrix, which can be physically realized, should be extracted. A hybrid algorithm is presented for the extraction of coupling matrix of the generalized chebyshev filters with direct source-load coupling and indirect source-load coupling. The coupling matrix of multiple-band bandpass filters are extracted with transmission zeros both in the passband and in the stopband. The coupling matrix of generalized chebyshev bandstop filters are synthesized by traditional methods. At last, the group delay characteristics of bandpass filters are analyzed.2. The study of modeling of four-port rectangular junctions, multiple-stepped bend and T-septum junction by full-wave mode matching method.Four-port rectangular junctions are the key blocks in the design of passive devices such as: cross-coupled combline filters. Multiple stepped rectangular waveguide bend and T-septum rectangular waveguide junction are the key blocks in the design of waveguide filters and diplexers. The above-mentioned junctions and bend are modeled by full-wave mode matching method. The odd-even mode theory is adopted to simplify the deduction of formulation and computation codes in the process of modeling. The former computation codes are supplemented.3. A series of microwave filters and diplexers are designed by optimization and fabricated based on HFSS and the programs written by myself.A combline SIR cross-coupled filter is designed by HFSS. Cha.5 presented the design of dual-band bandpass filter and corner diplexer. Serval new components are designed in Cha.6 based on substrate integrated waveguide (SIW) technique such as: multiple-band bandstop filter, generalized chebyshev absorption filter and diplexer. The multiple-band bandstop filter is based on proposed transveral coupling network for broadband applications. Experimental results have proved the validity of the analysis, programming and design methods.