Design And Realization Of Several Electronically Adjustable Microwave Filters

As the development of wireless radio frequency communication matures,the demand for frequency bands and space is increasing,and the limited spectrum resources become more and more crowded,which brings new challenges to the front-end radio frequency communication system.High-gain tunable antennas,tunable filters with high selectivity and high isolation,and tunable low-noise amplifiers with large signal-to-noise ratio are currently urgent needs.Traditional tunable filters mostly adjust single parameters of the filter,The application is very narrow.In this paper,the design of the adjustable filter based on the varactor diode not only realizes the continuous adjustment of the filter center frequency,bandwidth and transmission zero point under voltage control,but also ensures that the absolute bandwidth is constant during the process of center frequency adjustment.The development of communication systems is of great help.Starting from the basic tuning parameters of the tunable filter,this paper analyzes the realization principle of tuning based on different parameters of the varactor diode,supplemented by the traditional low-pass prototype design theory of the filter,and proposes to load the slow wave structure to adjust the center frequency,using The design method of hybrid coupling strength control transmission zero point may be helpful for the future development of tunable filters in RF front-end.Starting from the analysis of the periodic slow wave structure,the principle of realizing the adjustable center frequency is simulated and analyzed.On this basis,a UIR filter with adjustable center frequency and bandwidth is designed using a varactor diode.The test results show that the in the process of center frequency tuning,mode separation can be adjusted to control the absolute bandwidth of the filter to remain constant.Next,due to too many tuning parameters,in order to ensure that the power supply DC loops of multiple varactor diodes do not interfere with each other,a ?/ 4 SIR resonator was selected for analysis and design.Based on the hybrid coupling principle,second-order and third-order adjustable The center frequency of the filter and transmission zero are adjustable.And on this basis,a low-pass-band-pass switchable tunable filter is designed using PIN diodes,and the test results show that it has good out-of-band rejection.Finally,two dual-passband tunable filters were designed based on the UIR and SIR structures mentioned above.The center frequency and transmission zero of each passband are adjustable.The final experimental simulation results show that although the third-order and double-passband tunable filters have too many tuning elements and the order is too high,some of the indicators are not ideal,but they have completed the theoretical analysis of the center frequency,bandwidth,and transmission zero.All adjustable filter design.The tunable filters designed in this paper are all structures using microstrip planar resonators,and the coupling method is also using electromagnetic coupling.This feature allows the filters designed in this article to be designed to a higher order,so that they have more Good performance.And because of its microstrip planar structure,it is easier to integrate with other RF devices,which has high research value and significance for RF front-end systems.