Research And Design On Key Technologies Of Microstrip Reflectarray Antenna

High-gain antennas are an essential component in many wireless communication systems such as satellite communications,remote sensing and military radar.Microstrip reflectarrays are now emerging as a new generation of high-gain antenna for wireless communications due to its various advantages such as low profile,low mass,ease of manufacturing and ease of polarization transformation.In this paper,we mainly concentrate on some key issues of microstrip reflectarray antenna design,i.e.,dual circularly polarized(CP)reflectarray,beam-scanning reflectarray,low-profile reflectarray and beam-shaping reflectarray.The contributions and novelties of this thesis can be summarized as follows:1.A broadband single-layer,dual CP reflectarray with linearly polarized(LP)feed is introduced.To reduce the electrical interference between the two orthogonal polarizations of the CP element,a novel subwavelength multi-resonance element is proposed,which presents a broad bandwidth and a phase range excessing 360 o simultaneously.In the process reflectarray synthesis,we extend the conventional phase matching method(PMM)in frequent domain into polarization domain.Then,a single-layer offset-fed 20×20-element dual-CP reflectarray has been designed,simulated and fabricated.The simulated and measured results show that the 1-d B gain and 3-d B axial ratio(AR)bandwidths of the dual-CP reflectarray can reach 12.5% and 50%,respectively.2.A novel wide-angle beam scanning phase synthesis method is introduced in this thesis.In reflectarray beam-scanning application,the effects of incident angle are generally neglected or suppressed.On the contrary,in this thesis,we for the first time demonstrate that the effects of incident angle can be used to improve the scanning capability of reflectarray.Meanwhile,we develop the traditional frequency-domain PMM into spatial-domain PMM.Then,a 16×16-element reflectarray antenna has been designed,simulated and fabricated.The measured results show that a gain variation less than 1.7d B across the scan coverage from-45 o to +45o can be achieved by mechanically rotating the feed antenna,which shows a considerable improvement in beam scanning performance as compared to the reflectarrays designed using conventional single-focus and bifocal methods.3.This thesis propose a novel hybrid antenna configuration,which combines two kinds of high-performance antennas,i.e.,reflectarray and transmitarray,creating a low-profile,low-cost and low-mass design with both amplitude and phase distribution controls.In this hybrid arrangement,a flat Cassegrain reflectarray with compact ring focus is implemented as the feed to illuminate the upper transmitarray.In the process of reflectarray design,the particle swarm optimization(PSO)technique is utilized to synthesize the phase distribution on the reflectarray aperture to generate a desired amplitude distribution on the upper transmitarray aperture.In the process of transmitarray design,the dimensions of the double loop elements of the upper transmitarray are adjusted to compensate the phase delay of the wave from the lower reflectarray and form a desired phase distribution on the transmitarray aperture.A detailed design procedure for a Cassegrain-reflectarray-fed transmitarray antenna with a small focus-to-diameter ratio(F/D)of 0.3 is presented.The simulated and measured results demonstrate that this hybrid-configuration antenna can achieve an aperture efficiency of around 40%.4.A nonuniform frequency selective surface(FSS)-backed reflectarray with both amplitude and phase controls for beam shaping is introduced.In the process of element design,a dual-resonance reflectarray element backed by a loop FSS is studied.By tuning the dimensions of the upper reflectarray and lower FSS layers,the element can achieve a reflection phase of 570 o and an amplitude control range over 10 d B.In the process of reflectarray synthesis,a complex amplitude synthesis(CAS)technique,based on the modified alternating projection method(APM),is developed to take the physically realizable amplitude and phase controls of the FSS-backed element into account for optimizing the amplitude and phase distributions on the reflectarray aperture.A nonuniform FSS-backed 16×16-element reflectarray with a sector beam in the azimuth plane and a pencil beam in the elevation plane is designed and fabricated.The simulated and measured results show that this reflectarray antenna features a high-quality pattern with lower side lobe level(SLL),lower cross-polarization as well as lower radar cross section(RCS),compared to the reflectarray designed by conventional phase-only synthesis(POS)technique.