Research And Design Of Microstrip Tunable Filters

In recent years, with the development of wireless communication technology,wireless communication system on the filter requirements are more and more. And most of the spectrum concentrated in the low and intermediate frequency, resulting in a severe spectrum congestion problem. Microwave filter is an indispensable filter element in the communication system, the whole system is closely related to its performance. Modulation of the useful signal frequency, to eliminate the interference frequency, support multi-channel communication requires tunable filter this key device.Based on the basic filter theory, this paper introduces the design method of microstrip filter by introducing a large number of references, and then proposes several methods to design tunable filter, and choose one of them as the research object. The main contents of this paper are as follows:1. Introduction filter technical parameters and the basic theory, analysis of several electrical characteristics and advantages of tunable filter.2. A band-pass filter based on circular resonator is designed by microstrip resonator theory. This filter size is 16mm * 10mm * 1mm, insertion loss is greater than -2dB,the minimum return loss is less than -20dB,by processing into the physical and measurement, proved the design of the correctness.3. In the triangle resonator on the introduction of media substrate integrated waveguide thinking,through the metal hole to short-circuit metal,the design of a dual-pass filter, insert the loss to a large surplus -3dB, the minimum return loss is less than -20dB, through simulation analysis and discussion, validation The correctness of the design.4. Study electrically tunable filter design methods, variable-load diode-type microstrip tunable filter is designed by using the step impedance resonator coupling cascade method. the tunable filter has one of the passband unchanged, the other passband bandwidth is relatively constant, but the center frequency changes the characteristics of the filter requires a minimum return loss should be less than -10dB,through simulation to determine the feasibility of the design.