Design Of X-band Wideband Tunable Filter

Due to the rapid development of radio communication technology,the application of microwave and millimeter wave system has become more widespread,but it also brings the serious shortage of spectrum resources.As an indispensable part of microwave reconfigurable systems,tunable filters can not only effectively utilize spectrum resources,but also greatly reduce the volume and complexity of communication systems.Therefore,it has received increasing attention from researchers.This thesis mainly studies the design of bandwidth and center frequency adjustable filters for loaded varactor diodes.The details are as follows:1.A bandwidth-constant center frequency tunable filter with one transmission zero on each side of the passband is designed based on a second-order quarter-wavelength SIR Electrically coupled resonator.The bandwidth can reach 1.5GHz.On this basis,a fourorder filter with constant bandwidth and tunable center frequency is designed.The center frequency tunable range is 1.07 GHz,the out-of-band remote rejection is less than-36 d B,the insertion loss is less than 6.2d B,and the filtering performance is better.2.The feed structure of parallel-coupled line-loaded varactor is analyzed,and the external quality factor is adjusted by this structure.On this basis,combined with the multi-mode resonator structure,the design flow of the tunable filter is given.(1)Broadband tunable filter based on SLR dual-mode resonance.The center frequency is adjustable from 8.32 GHz to 10.8GHz,the upper band tuning range is 8.68 GHz to12.1GHz,the lower band tuning range is 8.03 GHz to 9.67 GHz,the bandwidth is adjustable from 4.07 GHz to 0.72 GHz,the variation range is 8.7% to 40.5%;(2)Fourmode resonant tunable filter based on fully symmetric loading open-circuit branch.The center frequency of the tunable bandpass filter can be continuously tuned between8.15 GHz and 10.89 GHz,the upper band tuning range is 8.5GHz to 12.1GHz,the lower band tuning range is 7.92 GHz to 9.81 GHz,and the bandwidth is adjustable from 0.7GHz to 4.18 GHz.The range was 8.6% to 43.3%.(3)Broadband tunable filter based on cross three-mode resonance.The center frequency of the tunable bandpass filter can be continuously tuned between 8.32 GHz and 10.75 GHz,the upper band tuning range is9.4GHz to 12 GHz,the lower band tuning range is 8.0GHz to 9.37 GHz,and the bandwidth is adjustable from 4.02 GHz to 1.53 GHz.The range was 17.7% to 40.2%.These three filters have the advantages of wide tuning range,zero transmission and low insertion loss in both upper and lower passband.