Design And Implementation Of Differentially-fed Antennas And Corresponding Feed Networks

Differential RF front ends became one of the research focuses due to their anti-interference property,which is particularly prominent,nowadays,with a variety of het-erogeneous networks coexisting.Confronted with the demands for differential RF front ends,researches pay more attentions to differentially-fed microstrip antennas.This thesis focuses on the differentially-fed circular microstrip antenna,the higher-order differential mode of the proposed antenna is analysed,as well as the proposed differentially-fed an-tenna arrays and their corresponding differential feed networks.The main contents and contributions of this thesis are as follows:First of all,a novel differentially-fed circular microstrip antenna is proposed.Based on the cavity model,the differential modes,which could be excited in circular patch an-tenna,are analysed.And the prototype of the proposed antenna is designed,implemented and measured.The higher-order differential operating mode,the differential quasi-TM₀₁mode,is introduced initially.The electric fields distribution and the radiation character-istic are presented then.Unlike conventional TM₀₁-mode circular patch antenna,which has monopole-like radiation patterns,the proposed antenna has maximum radiation in broadside direction,which is more like the TM₁₁-mode one.In addition,according to the measured results,a high gain of 10.27 dBi is achieved due to the higher-order differential mode.Besides,benefit from the differentially-fed mechanism,a weak cross-polarization is obtained.Additionally,high-gain differentially-fed circular patch antenna array are proposed.Based on the definition of the mixed modes,a pair of differential ports of the array element could be regarded as one single signal mode.Thus,the conventional method for array synthesis could be applied for designs of differentially-fed arrays.Initially,the proposed high-gain differential circular antenna is adopted as the array element,and the elements are placed in the H-plane to pursue a high gain.On the basis of uniform differentially-fed array,the ratio of the input powers of the differential signals are adjusted to 1:2:2:1,so that the radiation characteristic could be further enhanced,and the side lobe level is reduced.In the end,the proposed uniform and nonuniform differentially-fed circular patch antenna arrays are fabricated and tested with the corresponding differential feed networks.Finally,the corresponding differential feed networks of the proposed differentially-fed circular patch antenna arrays are presented.Based on the single-ended-to-balanced power divider,those differential feed networks are designed and implemented.To meet the demands for differentially feeding,the Wilkinson power dividers and the single-ended-to-balanced power dividers are cascaded.When single-ended RF signal enters the input ports,the ratios of the power of the differential output signals are 1:1:1:1 and 1:1:2:2,respectively,which meets the feeding demands of the differential arrays and provides a new method to feed the differential array.