Inhibition Of The Parasitic Passband Filter Technology

Filter is the key component of radar, communication and testing system, which is used to transmit signals in pass-band and enable signals in stop-band.As a result of multi-modes of microwave resonator, harmonic is a character of microwave filter. In microwave communication system, this character maybe not enable noise, especial in multiplexer and EMI filter, so how to supurious harmonic is an important research direction.The thesis focuses on supurious second pass-band of cavity filter.At first, the thesis analyzes the principle of microwave filter. By the equivalent circuit of resonator working in filter, we can find the reason of second pass-band and how to avoid this: equally space the second resonances over a frequency range; push the second resonance far away form pass-band; design the coupling structure to stop the higher modes.In empty resonator filter, we improve stop-band performance using different widths, the stop-band is wider than standard filter. Capacity-loaded resonator have the second resonance far away form fundamental mode; A filter using it is designed and tested. Absorbing material can absorb high frequency electromagnetic wave; the coupling structure with is material can stop the propagation of high modes. scientific experiments are conducted to prove the efficiency.As one coin have two faces, the three methods have advantages and disadvantages. We can choose the right way in engineering.