The Integration Design Of Micro-strip Filter-antenna

Antenna and filter are two important components of the warship's RF front end,which plays a very important role in the overall performance of the system.The traditional method is to design the antenna and filter independently,and then use impedance matching circuit to connecte them.This method increases the complexity of circuit design.Therefore,in this paper,the integrated design of the antenna and filter is adopted by the filter synthesis method which eliminate the impedance matching design,reduces the overall size and loss.The main research content and research results of this paper include the following aspects:1.A microstrip bandpass uniform impedance filter-antenna is designed by the filter integrated design method.The filter-antenna consists of two microstrip uniform impedance hairpin resonators,a parallel coupling line and an inverted L antenna.The design method is to use the antenna to replace the last resonator of the filter.The resonator is coupled to the antenna by the parallel coupling line,and the filter antenna is obtained.The designed filter antenna has both the filtering performance and the radiation performance.The filter antenna is integrated.Compared with the method of direct cascade of filter and antenna,it does not need to design matching circuit,simplifies the design of the circuit,and reduces the size and loss of the system.2.In view of the problem that the uniform impedance filter has parasitic passband in the frequency doubling section,the Stepped Impedance Resonator(SIR)is used to replace the uniform impedance resonator in this paper.SIR is made up of two microstrip lines with different widths.The position of the parasitic passband of the resonator can be changed by adjusting the width ratio and the length ratio of the microstrip line.By introducing the SIR resonator,the frequency of the first parasitic passband is extended from 2 times to 3 times the fundamental frequency,and the band width of the filter antenna is greatly improved.3.In view of the problem that the antenna is easily interference from neighbor frequency signal with the densy frequency spectrum in ship's platform,cross coupling structure is proposed in this paper to make the filter-antenna generate two transmission zeros in the sideband,which greatly improves the sideband selectivity of the filter-antenna and reduces the interference from the neighbor frequency signal.