Research On Dual-polarization Microstrip Filter Antenna Based On Differential Feed

The RF front-end system plays an important role in wireless communication systems,connecting free space and intermediate frequency signals transmission.And in the RF front-end system,filters and antennas are two important passive devices,which determine the overall performance of the whole system.Higher performance,miniaturization and portability of modern microwave communication systems are required for the RF front-end circuits.In order to realize the miniaturization of the RF front-end system,the filter and antenna can be co-designed,which can not only reduce the size and costs of the system,but also improve the overall performance of the system.In this thesis,a series of filtering antennas with great performance have been thoroughly studied.The main contents of this thesis are as follow:Firstly,this paper introduces the research background and significance of the filtering antenna,summarizing the research status of filtering microstrip antennas at home and abroad,and also analyzes the existing problems and technical challenges.Secondly,to this problem,this paper studies the design method of antennas which possess filtering response,then proposes three novel filtering antennas,which ensure the antenna radiation performance and achieve good filtering characteristics.In addition,no additional filtering circuit is introduced.Moreover,these antennas adopt differential-feed and strictly symmetrical structure,thus low cross-polarized and symmetrical radiation patterns are obtained.Detailed description is as follows:(1).Dual-band dual-polarized differential-fed filtering antenna element and array.In this part,a dual-band dual-polarized filtering antenna by loading a cross-slot and parasitic strips is proposed.The filtering response is realized by introducing two radiation nulls between two close operation bands,where the isolation is greatly improved.Without additional filtering circuit,almost no extra insertion loss is introduced to the antenna.Therefore,the dual-band and dual-polarized antenna with filtering performance is realized in a compact and high-gain structure.(2)Dual-polarized differential-fed filtering antenna based on DGS-pins structure.In this part,two different dual-polarized differential-fed filtering antennas are designed based on the DGS-pins structure.One uses DGS-pins and V-shaped open stubs to produce radiation nulls at both edges of passband,thus improving the frequency selectivity and achieving filtering performance.Meanwhile,the DGS-pins structure can generateadditional resonance in the passband to enlarge the operation bandwidth.Finally,a dual-polarized differential-fed filtering antenna with enhanced bandwidth and good filtering performance is realized.For the other antenna,by loading DGS-pins and a cross slot structure,a radiation null is respectively introduced at each edge of the passband,which sharpen the roll-off rate of two edges.Therefore,the filtering response is embedded into the antenna element without extra circuit.In addition,the DGS-pins and cross slot structures can also respectively generate an additional resonance in the passband,which greatly broadens the impedance bandwidth.Finally,a wideband dual-polarized differential-fed filtering antenna with compact and high gain is realized.(3)A dual-polarized differential-fed filtering antenna with second-order harmonic suppression.In this part,on the basis of differential-feed,a dual-polarized filtering antenna with second-order harmonic suppression is designed.By loading the ?/4and ?/2 wavelength open stubs,two gain nulls are produced at both edges of the passband,which improves the skirt selectivity,achieving the filtering response without the radiation performance of the antenna influenced.Finally,the antenna obtains a good filtering performance and wide bandwidth of suppression at high stopband,featuring the second-order harmonic suppression.