Design Of High-performance Waveguide Low-pass Filters

With the rapid development of modern microwave communication techniques, the peak and average power of the high-power microwave equipment, such as radar, tend to be higher. However, for a transmitter with higher transmission power, it is difficult to achieve satisfying harmonic spectrum purity. The radiation energy may increase to, or even exceed, the working power of communication devices, which will severely interfere or destroy the devices.Therefore waveguide harmonic filters are usually employed for restraining the harmonic.The harmonic controlling capability of the traditional stepped impedance lowpass filters is usually weak, with only 1.5 times of cut-off frequency, which cannot meet the harmonic controlling requirement of satellite communication nowadays. In this thesis,on the basis of lumped parameter filter,we designed a tapered corrugated waveguide by changing b side to improve harmonic restrain.The filter can control the frequency up to 2.5 times of cut-off frequency , significantly spread the stop band and enhance the performance of filters.In addition,it is designed onveniently,manufactured simplely and debugged easily.We do not have the related reports of the waveguide filter structure in the domestic literature.The contributions of this thesis are listed as follows:1) Systematically analysis the theories of the design of microwave filter, including the transfer functions,low-pass prototype filter,frequence transformations , immittance inverters and systermatic summary of the filter design.2) Intoduce the methods of harmonic rejection and discusse the specific mothods of parameter extration of lumped/distributed filter prototype element values. The shunt capacitor and characteristic impetance are achieved with waveguide, based on which the phase of the shunt capacitor was exactly corrected.3) With the specific design requirements,17 and 7 degrees tapered corrugated waveguide filters were designed.The optimum size of filters was determined after the analysis of electromagnetic simulation software CST. After simulation and adjustment, the fabrication of the 7 degrees low-pass filter was conducted and tested.At last, the improvements were proposed after comparatively studying the measurement results and simulation results.