Dual-frequency Dual Circular Polarization Sequential Rotating Microstrip Array Research

Circularly polarized_CPantennas have many advantages such as insensitivity to polarization locations,elimination of the signal Faraday rotation effect caused by the ionosphere,and strong anti-interference ability.Therefore they are widely used in satellite communication,radar,GPS and other systems.Meanwhile,dual-band dual-polarization shared-aperture antennas are usually adopted in satellite communication systems.In this thesis,the sequentially-rotated_SRarray is studied thoroughly to develop a dual-band dual-CP SR microstrip array with high gain at X bands for a specific satellite communication system.The main work is shown as follows:Firstly,research status and progress of CP microstrip antennas are summarized.The SR feed technique and its mechanism of broadening bandwidth are studied.Also the bandwidth and spacing of the SR array with different polarized elements have been discussed.Secondly,a dual-band dual-CP SR microstrip sub-array with single-layer substrate is proposed at X-band.A rectangular patch is used to produce dual-band dual-linearly radiation with high polarization isolation.Then a 2 by 2 dual-band dual-CP sub-array is composed by two independent sets of feed structures.The two operating frequencies with a ratio of only 1.05 have been achieved.Linearly-polarized modes provide a good isolation at two close frequencies.Furthermore,the SR array has good circular-polarization and bandwidth charateristics.Thirdly,an 8 by 8 array is designed to obtain high gains with a single-layer substrate.It constructed by the 2 by 2 sub-arrays through two sets of parallel feed networks.Then by utilizing miniaturized power dividers and semi steel coaxial cables,a 16 by 16 array is further developed.Mesured results show that the-15dB impedance bandwidths of 2.2%and 2%,isolations of-18.6dB and-19.4dB,3dB axial ratio bandwidths of 2.84%and 1.57%;peak gains of 25.1dBi and 25.6dBi are obtained in the lower band and higher band,respectively.Finally,measurement on CP antennas is corrected and improved based on a linear component method.By utilizing only two sets of orthogonal linear polarization amplitudes,without phase information,accurate measurement on axial ratio can be realized.Co-polarization and cross polarization pattern can be further obtained.Measurement on gain is also given.