| High-gain antennas are extremely desirable in long-distance co mmunications,radar system,and space exploration,etc.Because of the favorable merits such as low cost,low mass,and ease of fabrication,planar lens antennas are now emerging as an attractive candidate of high-gain antennas,and have attracted growing attention in academia and industry.The main focuses of this dissertation include wideband single-fed planar lens antennas,low-profile and wideband array-fed planar lens antennas,beam scanning phased planar lens antennas,vortex beam-generating phased planar lens antennas,and integrative planar lens antennas co-designed with gain-filtering and low-scattering characteristics.The main novelties of this dissertation are su mmarized as follows:1.A wideband multilayer frequency selective surface(M-FSS)planar lens antenna fed by a horn is proposed.The employed elements composed of dual-resonance double hexagonal rings are closely arranged in the honeycomb lattice.The results show that the planar lens can achieve a 53.34%peak aperture efficiency and a 19.23%bandwidth for1-d B gain drop,respectively.2.A wideband polarization-rotation horn-fed planar lens antenna is proposed.The wideband element is with three metallic layers,where a split circular ring connected by a narrow strip is in the middle layer,and two polarizers are in the upper and bottom layers.After modeling the horn-fed planar lenses,an optimization method is introduced to design the wideband lens that follows the bandwidth definition of 1-d B gain drop.The results show that its bandwidths of 0.5-,1.5-and 3-d B gain drop are 41%,56%and71%,respectively.Moreover,a peak aperture efficiency of 40.7%is achieved.3.An array-fed planar lens with low-profile and wideband features is proposed.The conjugate field matching(CFM)technology is utilized to realize an ideal compensation.A small-scale dipole antenna array,which has a nearly identical aperture size to the feed horn,can effectively excite the planar lens with a profile reduction by64.5%.4.A Vivaldi array-fed planar lens with low-profile and ultra-wideband properties is proposed.After modeling the array-fed planar lenses and constructing the fitness functions,a three-step optimization process is introduced to determine the planar lens element arrangement as well as the array feed excitation coefficients.The results show that stable radiation patterns with good main beam shapes and reasonable sidelobe levels are obtained in 5～19 GHz(3.8:1).5.Planar lens antennas fed by phased array antennas(PAAs)for beam scanning applications are proposed.After thoroughly analyzing the operating mechanisms of the PAA-fed planar lenses,the active element-lens pattern(AELP)method is introduced to determine the PAA feed excitation coefficients.Three experiments are performed in microwave band,millimeter-wave band,and terahertz regime,respectively.6.A defocused cylindrical dielectric Luneburg lens antenna with PAA feed is proposed.A 19-element dipole PAA,which has been partitioned into three linear subarrays,illuminates the defocused lens with the weighted excitation coefficients optimized by the AELP method.Results show that the proposed PAA-fed defocused lens features a high-precision scanning across an ultra-wide angular range of±81°with a 21.1 d Bi peak gain,3/7.5 d B gain drops as scan to 75°/81°,respectively.Besides,against traditional cylindrical Luneburg lens with switched feed elements,5.4～3.3 d B gain enhancements and 11.9～6.6 d B effective isotropic radiated power(EIRP)improvements are obtained.7.A planar lens antenna with a small-scale circular PAA feed is proposed to generate angular momentum(OAM)-carrying radio beams.The steering of the zero-OAM-mode beam across an angular range of±25°is realized.Meanwhile,the creation of multiple pure or mixed OAM beams with helical phase fronts is also presented,where the superposition of multiple OAM states provides more possibilities to increase the channel capacity and spectrum efficiency.To facilitate the experiments,an 8×8 Butler matrix with a bandwidth over 30%is designed,which integrated with the array-fed TAA also provides an attractive solution to simultaneously generate multiple OAM modes without requiring any active modules.8.An integrative planar lens with gain-filtering response,high-gain in-band radiations at X-band and out-of-band low-scattering characteristic is proposed.The integrative planar lens element consists of a dual-polarized resistive sheet,a fixed bandstop M-FSS element,and an adjustable bandpass M-FSS element also serving as the phase shifter.The results show that the integrative lens can realize out-of-band suppression levels≥25 d B,～8 d B radar cross section(RCS)reductions in 4～7 GHz and14～20 GHz,and the radiation gain of 25.3 d Bi simultaneously.9.An integrative planar lens,which is combined of a bandpass M-FSS and a square dielectric post with antireflection pyramidal structures(SDPP),is proposed.The element achieves the simultaneous control of in-band transmitted waves and out-of-band reflected waves.The SDPP elements with different heights are utilized to reduce the RCS based on the phase cancellation principle.The results show the SDPP array can realize the RCS reduction in a 10:1 bandwidth up to 60°,including～5 d B/～10d B RCS reductions in 0.5～1.5 f_c/1.5～5 f_c,respectively,together with gain-filtering responses with out-of-band suppression levels higher than 20 d B. |
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