Design Of Microwave Electronically Filter

With the rapid development of communications, so that spectrum congestion is getting worse. Then the applications of microwave filters increasingly spread. Application of spread spectrum allocation technology of multi-frequency and dynamic frequency, we hope RF devices, especially filter, to meet the needs of fast electric tune or reconfigurable. So a well-designed electrically tunable filter or reconfigurable filter both for theoretical research and engineering applications is very important.This paper studies two novel electrically tunable microwave filter design methods and basic principles, one is four microstrip tunable filter, the other is a helical filter with back cavity in VHF. Here we have studied and completed the following aspects:1. Surveying the development and the status of the electrically tunable filters, which shows the electrically tunable filer is so important in both theoretical and practical.2. This paper introduces a low-pass filter which comprises a prototype of low-pass filter, transverse of filter and so the most basic design theory, and then make a summary of the development and the status of the electrically tunable filters.3. Based on the theory of SIR, a compact four-band filter working at 4.0G / 5.1G / 7.1G /8.5G was designed, and by using variable capacitance and external bias circuit, then the third/fourth passband can be tuned, use IE3 D and ADS software co-simulation to study the tuning mechanism and tuning range, an then through simulation and machining test illustrate the passband characteristic of this filter was not good enough.4. By using stub-loaded resonator, a four-passband microwave filter was designed which working at 2.4G/3.5G/4G/5.2G, after the introduction of variable capacitance tube power transfer technology to achieve a continuously adjustable passband 2.4G and 4G.5. Based on the helix cavity filter and back cavity resonator, a two-order helix filter working at VHF was designed, back cavity resonator which introduced a zero in stopband can improve band rejection greatly. Capacitance matrix switch access PIN is in left and right ends of the helix filter, by controlling the PIN switch to change the capacitance value of the circuit, then the frequency of passband can be tuned. Simulation design an electric tunable filter whose center frequency of passband is 30-88 MHz and stopband transmission zeros can be tuned synchronize, providing a reference for the next project application.