Design And Simulation Of Microwave Filters

Radio telescope is the foremost tool for radio astronomical observations. Because of the further study of astrophysics, astronomers put forward higher requirement for the performance of the radio telescope. Sensitivity and resolution are two most important factors to measure the performance of the radio telescopes. The angular resolution is mainly determined by the size of the telescope; while the sensitivity is depend on the performance of the microwave receiver. As a frequency selection essential element of the receiver, microwave filter will directly affect the performance of the receiver, and thereby will affect the sensitivity of the radio telescopes.According to the special radio observations requirements and receiver performance at L, S-band of the25m radio telescope in Nanshan Base of Xinjiang Astronomical Observatory, in this paper we determine the filter design requirements, and use the ADS software to design and simulate the two microstrip bandpass filter.In this paper, we introduce the basic principles of both microwave filters and microstrip line, then comparative and analyze the classical theory and method of several microwave filter designing. Besides, according to both of the relationship between frequency changing and structural parameters of the microstrip line filter and design requirements, we decide to adopt the Chebyshev low-pass prototype filter, and use ADS software to simulate and optimize the initial value of the geometric parameters of two microstrip filters in L, S-band, in which the L-band microstrip filters uses the hairpin structure, and the S-band one uses the coupling structure parallel. The simulation results shows:L-band filter bandwidth400MHz, differential loss of0.78dB, return loss-20.4dB; S-band filter bandwidth of240MHz, differential loss of0.95dB, return loss-24.7dB. Both simulation results meet the design requirements, and its performance is better than that of the two filters which are currently used at Nanshan25m radio telescope. Finally, we analyze the effect in the performance with the physical parameters of the filter and its material, and obtain the law curves, which, to some extent, improve the accuracy of the microwave filter design, and shorten the design cycle.