Research On High-gain Microstrip Antennas Based On Higher-order Modes

With the rapid development of millimeter wave(MMW)and terahertz(THz)wave systems,high frequency band antennas are attracting more and more research interest recently.High gain microstrip antenna based on high-order mode has the characteristics of electrically large property and high gain,which can overcome the problems of high fabrication accuracy requirement for MMW and THz devices and high propagation loss in this frequency band.In this paper,linear polarization,circular polarization and beam tilt microstrip antenna with high gain based on high order mode are studied.The main contents are as follows:Firstly,the linear polarization high gain microstrip antenna based on high order mode is studied.By combining the differential feed and current interference technology,the patch can work in the high-order resonance mode can maintain uniform current distribution,and the microstrip antenna with high broadside gain can be realized without using the array configuration.For 12 GHz frequency,the gain and efficiency of the high-order mode microstrip antenna are optimized,and the patch based on TM90 mode is designed.The gain is 16.1d Bi,aperture efficiency is 69.4%,sidelobe level is-17.2d B,cross polarization is-31.9d B,impedance bandwidth is 4.8%,measured antenna impedance bandwidth is 3%,maximum gain is 15.3d B,sidelobe level is less than-16.4d B,cross polarization is-28 d B.Secondly,a circularly polarized high-order mode microstrip antenna is proposed.A circularly polarized antenna with high-order mode resonance can be obtained by loading a rotating dipole array above the linear polarized high-order mode antenna.The mechanism of circularly polarized radiation is described,and the optimal design of loaded dipole is discussed.A left-hand circularly polarized microstrip antenna based on TM90 mode is designed,The simulation results show that the maximum gain is 15.9d Bi,the impedance bandwidth is 8.7%,the 3d B axial ratio bandwidth is 6.6%,and the gain in the axial ratio bandwidth is more than13.5d B.The test results show that the peak gain of the antenna is 15.5d Bi,the sidelobe level is lower than-15.6d B,the cross polarization is lower than-17.3d B,and the working bandwidth is 6.5%.Thirdly,a method is proposed to make high-order mode microstrip antenna with tiltedbeam.By adding a transmission type electromagnetic surface directly above the antenna,the transmission phase of electromagnetic wave is controlled with a high transmission amplitude,and a progressive phase shift is realized,so that the maximum radiation direction of the antenna is deflected.A TM90 mode microstrip antenna with beam deflection of 10° in E plane is designed.The simulated peak gain is 16.2d Bi and the bandwidth is 7.2%.The measured antenna peak gain is 15.4d Bi,the side lobe level of E plane is lower than-15.8d B,the cross polarization is lower than-26 d B,and the working bandwidth is 5.4%.The high-order mode microstrip antenna studied in this paper can achieve high broadside gain with electrically large property without complex feeding network,and the flexible highorder mode selection can meet the requirements of different aperture sizes;the function expansion of circularly polarized radiation and beam scanning is realized by loading the electromagnetic surface above,so that the high-order mode antenna maintains the same function control as the antenna array.The related technology can be used in the design of electrically large antenna in high frequency band such as MMW and THz,which is of positive significance to adapt to the development trend of higher and higher working frequency band of communication and detection system.