Coaxial Waveguide With Dual Media Filter Design And Analysis

In view of the importance of filters in microwave devices, we designed and analyzed three kinds of filters: coaxial filter, waveguide filter and dielectric dual-mode filter, which can be applied in different situations. The related techniques and theories are researched during the design process.At first, the thesis proposes a practical method for designing a coaxial stepped impedance filter accurately, started from the principle of transmission line. After taking the edge capacitance, shunt equivalent capacitance and series equivalent inductance into account, which could be neglected in model theoretical parameters calculation before, and combining the edge capacitance formula and iterative formulas, the accuracy of the design is improved effectively. The simulation results verify the improvement according to that it consistent with the general requirement.Secondly, the thesis designs and analyzes a rectangular waveguide filter with transmission zeros based on the coupling matrix theory. To satisfy the pseudo-passband isolation and high-power design requirements, we weigh the relationship between cavity size and the eigenmode frequency and cavity Q value. Cross-coupling is implemented in four cavities structure according to the cross coefficient of coupling matrix calculated after adding transmission zeros. It is an effective waveguide filter design way to realize transmission zeros and reject the adjacent channel sufficiently.Finally, we introduce the design principle and calculation method of dielectric dual-mode filter with two cavities. The resonant frequency of dielectric square resonator located in a rectangular shield is analyzed with Eigen function match method; the iterative equations are given then. Meanwhile the designed structure is simulated by Ansoft HFSS. The filter uses chamfer to couple dual resonant mode and utilizes coupling rod combined with iris coupling window to couple two cavities in 4th-degree filter design to enhance couple bandwidth. The required parameters of the microwave band-pass filter: center frequency f₀ = 2140MHz, bandwidth BW = 50MHz, insertion loss IL <0.1dB , and return loss RL > 22dB . According to the result of simulation, the filter can reduce the insert loss and dimension efficiently. It's one of the most effective means for miniaturizing a band-pass filter.