Cavity Cross-coupled Band-stop Filter Analysis And Design

Microwave band-stop filters have been extensively used in telecommunication and broadcast systems, to suppress the spurious outputs from a high power transmitter and harmonic pass-bands from a nonlinear power amplifier or a band-pass filter. Traditional cavity band-stop filters with the structure of stubs are designed as a number of cascaded stub resonators of 1/4 wavelength, which are separated by about 1/4 wavelength. Stepped-impedance resonator (SIR) can be used to decrease the height of filters. Band-stop filters with the structure of waveguide are designed using resonators in 1/2 wavelength, which are separated by about 3/4 wavelengths in order to avoid the stray couplings. But cul-de-sac structure band-stop filters just apply this specialty to achieve cross couplings. When two signals of different frequencies pass one channel, which requires high selectivity to reject noise and interference, extra linearity near the edges of the channel, single-band band-stop filters can be extend to dual-band band-stop filters, which have excellent characteristics, are widely studied home and overseas. In this thesis, the main research contents are the principle, structure and realization of cavity band-stop filters. Two novel band-stop filters are designed with SIR and cul-de-sac structures, and then extend to dual-band band-stop filters. The main task are listed as follows:1.Introduce the basic structures and characteristics of SIR, and then present the design method of a band-stop filter with 1/4 wavelength SIR.2. Introduce the principle of cross coupling and the routing structure, particularly, the synthesis of coupling matrix and annihilation, and realize it by MATLAB. Combine the synthesized matrix with HFSS to design a cul-de-sac band-stop filter.3.Extend the dual-band band-stop filters from single-band band-stop filter, and realize it by MATLAB. For dual-band band-stop filters have highly sensitive, this thesis provides an improved coupling network on the basis of forementioned researches and designs a new dual-band band-stop filter.