Applications On Magnitude And Phase Modulation Technology In Array Antennas And Secondary Radiators

Amplitude and phase modulations have wide applications in array antennas.With the developments of frequency selective surfaces and EM metasurfaces,amplitude and phase modulations are efficiently realized in lenses,reflectarrays and partially reflecting surfaces(PRS).This thesis applies on the amplitude and phase modulations in array antennas and secondary radiators.The researches consist of five main contents:Firstly,based on the conformation and mirror slots in substrate integrated waveguides(SIWs),a high gain omnidirectional antenna is achieved after phase modulation.A compact two-layered SIW first-order-to-higher-order converter is designed according to the slot coupling theory.The first mode in the bottom layer couples to the top layer through the slots on the broad side,then the higher mode is formed due to equiamplitude and out-of-phase between adjacent coupled waves at same sides.The insertion losses of TE₈₀ mode is below 9.4d B.The gains of 8×8 slot array fed by TE₈₀mode converter is 21.2d Bi.The side lobe levels(SLL)are below-9.9d B,and the radiation efficiencies are above 87%.After circumferential comformation of the mode convertor axial conformation of the slots,a high gain omnidirectional antenna with 8.5d Bi gain and less than 2d B out-of-roundness is realized.Secondly,based on the ray and leaky wave model in Fabry-Pérot(FP)cavity,after amplitude and phase modulation,mutual coupling reduction between feeds and frequency scanning performance are researched,respectively.According to spatial decoupling method in FP cavity antenna array,surface wave is analysed alone without PRS,while scattered wave is analysed alone after electromagnetic bandgap structures(EBG)are added in temporarily.By means of adjustment on the distance between PRS and reflectarray,the scattered wave undergoes amplitude and phase modulations together in FP cavity.Then the scattered wave and surface wave cancel each other after the decoupling optimization.S₂₁ drops from-20d B to-30d B,with gain from 14.3d Bi to 13.6d Bi.In FP cavity antenna,the cell sizes vary with azimuth angle when the beam tilts,which increases the phase modulation efficiency.According to the frequency response characteristic of PRS reflection phase,scan angle decreases with frequency in forward region,while radiation in backward region has small contribution to the frequency scanning performance.Meanwhile,the feed bandwidth is wider thanks to stacked patches.The scan angle has the range of 24°from 9.4GHz to 10.6GHz in the proposed FP cavity antenna.The 3d B radiation bandwidth is 8.5%,with SLL below-7d B and radiation efficiency over 88%.The phase error analysis on PRS cell provides the possibility for the radiation in backward region to participate in the frequency scanning performance.Thirdly,based on the Fermat's Theorem,frequency scanning in multi-layered resonance and multi-beams in E-plane metal plates are achieved after phase modulation in lens.360°phase coverages are realized with four-layered resonance structure.According to the frequency response characteristic of lens cell transmittance phase,frequency scanning planer lens antenna is designed utilizing broadband quasi-Yagi antenna as the feed.The scan angle has the range of 13°from 8GHz to 11.8GHz.An integrated lens antenna is presented on the basis of the EM acceleration phenomena in E-plane metal plates.With the help of the spatial response characteristic of metal plate transmittance phase on the feed position,multi-beams lens antenna is proposed employing some high-gain quasi-Yagi antenna as the feeds.The beam direction ranges of the proposed lens antenna are both 30°in E-plane and H-plane.The gains for all feeds are above 22d Bi,with SLLs below-9.8d B and aperture efficicncies over 14%.Forthly,based on 2-bits phase quantization technology,in the reflectarray consisted of 2-bits phase quantized cell,beam steering and amplitude modulation are achieved after phase modulation.The cell includes three layers.On the top layer consisting of two switches is reflection phase shifter for 2-bits phase quantization.On the bottom layer is control circuit for switches conditions control.On the middle layer is ground to isolate the phase shifter and control circuit.The relationships between phase distribution patterns and beam directions are compared and analyzed.2-bits phase quantization technology meets the requirements of 2D beams control within 20 degrees.Meanwhile,the bigger of reflectarray sizes,the preciser of beam directions.Then,genetic optimization(GA)is utilized in directional function for low radar cross-section(RCS).Thus,the entire reflectarray obtains 85%amplitude modulation depth in scanning range.