Research On Low-profile Space-borne Antennas Using Characteristic Mode Analysis

In recent years,research on low Earth orbit(LEO)satellite communication constellations has become an upsurge.Many countries focus on promoting the construction of the satellite internet.To meet the demand of mass production and high integration,satellites for communication constellations are normally microsatellites with limited space,weight and power consumption resources to take full advantage of the launch capabilities of a rocket.Therefore,higher requirements have been put forward for the performance of space-borne antennas in inter-satellite communication,satellite-to-ground data transmission,and telemetry,track and command(TT&C)applications.This dissertation conducts the research on space-borne antennas with low profile,wide bandwidth,wide shaped beam,and wide-angle scanning using characteristic mode analysis(CMA),including the following three main parts:Firstly,due to the dynamic changes in satellite coordinates and its attitude,the beam tracking seems very difficult in inter-satellite point-to-point communication with high accuracy.To solve this problem,a low-profile retrodirective microstrip patch array with low cost is designed to realize the “self-steering” beam tracking.A simple chamfered square patch element is analyzed using CMA,based on double-mode circular polarization modulation.With the full use of the reciprocity of the passive mixer,a novel phase conjugating circuit can realize a coplanar layout to reduce the profile of the array further.The effects of up and down conversion loss deviation of mixers on the radiation pattern and the beam pointing error of the antenna are also discussed.The experimental results of a prototype of the proposed 1-D four-element array show a relatively good retrodirective performance.Secondly,to meet the demand of wideband communication in high-rate data transmission,a triple-mode wideband circularly polarized(CP)flat plate phased array is proposed to solve the difficulty in widening the bandwidth of existing patch antenna with single layer and single feed.In triple-mode wideband operation,three orthogonal polarized modes are excited simultaneously.By sharing one common mode,two pairs of CP modes with the same polarization rotation are formed to broaden the CP bandwidth of the antenna.Then,to settle the problem of high side lobe of the preliminary designed array consisting of off-center fed patch elements using sequential rotation technique,two solutions are proposed and studied.One is a technique of random sequential rotation;the other is an alternative center-fed patch array.Both techniques can effectively improve the array scanning performance including the gain,the axial ratio,and the side lobe level,etc.Thirdly,in order to reduce the weight,profile,and power consumption of existing beam-shaped antennas in telemetry,track and command(TT&C)applications,a quadruple-mode beam-shaped metasurface antenna(MSA)is proposed to provide an extremely low-profile beam shaping scheme with low cost and power consumption as well.Different from the above two research on the modulation of broadside radiated modes only,higher order modes with omnidirectional radiation are also considered in this work.Four modes include two pairs of modes formimg two CP modes with broadside and omnidirectional patterns,respectively.By exciting four modes simultaneously,the omnidirectional radiated CP mode can compensate for the dramatic reduction of the gain of the broadside radiated CP mode outside the half power beamwidth(HPBW).Therefore,the shaped beam with extended HPBW can be achieved.Guided by the method,a preliminary MSA is designed for the primary proof but with an unsymmetrical radiation pattern.A method for suppressing the unwanted higher order modes is then studied.An improved MSA structure is thus proposed with a more symmetrical beam-shaped radiation patterns by appropriate excitation.In summary,a systematic investigation on space-borne antenna design using CMA has been done in this dissertation,from a progressive mode modulation(from two modes to four modes)for enhancing its operating bandwidth and shaping its radiation patterns.The research trys to solve the main technical challenges such as low profile,wide operating bandwidth,wide beamwidth,and wide-angle scanning,met in inter-satellite and/or satellite-to-ground communication.