Research And Design Of Cavity Bandpass Filter

With the continuous improvement of people’s living standards, the requirements of quality and convenience of communication become higher. In order to meet the market demand,wireless communication technology has been greatly developed. Microwave filter is the most important filter element in communication system, and its performance is closely related to the quality of the whole system. The filter in the RF and microwave circuit plays an important role. Coaxial cavity filter is widely applied in modern wireless communication, digital television broadcasting and sarellite navigation systems, for its high power capacity, low insertion loss, far spurious pass-band.This research is based on the project of a mobile company. The filter to be designed meets the following requirements:the Center frequency is875MHz; the bandwidth is10MHz; the insertion loss is below0.25dB; the wave in the passband is below0.2dB; the out-of-band rejection is below-80dB@825-835MHZ and the return loss is above-20dB. Ahrough the theory of cross coupling of a coaxial cavity bandpass filter is designed in the paper using the AWR software and the HFSS software. And the performance of the designed filter is verifyed by the software of Matlab.Firstly, the research background,significance, status and important function of microwave fifter in the microwave communication is introduced, Then this thesis expound the basic theory of the filter characteristics and its network theory, summarize the design method of low-pass filter and the theory of lowpass to bandpass transformation. Based on filter’s mathematical model,this thesis introduces process and method that using AWR to compute,simulation and optimizate filter, Simulate3D mode in HFSS software using the theory parameters such as frequencyof cavity and the coupling coefficient of optimized filter. Design and simulate a coxial cavity bandpass filter according to the process and method,the filter has5resonators composed of two cross-coupler that introduces transmission zeroa to increase the filter band rejection level. In addition, the paper analyzed the influence of filter performance with coupling bar height, window size and tap location, then qualitatively got filter performance law curve with the change of those factors. In order to verify that the filter with high inhibition performance, the coupling matrix is integrated in the paper using the Matlab software, the band rejection, insertion loss and return loss of this filter can meet the requirements of indicators by analyzing the response of S parameters. The results show that using the AWR and HFSS software to design the coaxial cavity bandpass filter can be achieved with high inhibition performance.