Design Of Broadband/Multiband Directional Antennas Based On Mode Analysis

With the increasing demand for high capacity and high-speed wireless systems,it is essential to explore more effective spectrums,to improve the utilization of limited spectrums,and to meet the multi-performance requirements of different applications.Designing antennas with wide bandwidth,high radiation performance and low cost has always been a hotspot in wireless systems.Among them,broadband antenna can effectively alleviate the rapid growth of current communication,and the unidirectional antenna can increase communication distance and improve the anti-interference capability of the system.Therefore,three kinds of high performance broadband unidirectional antennas based on electromagnetic(ME)dipole and metasurface(MTS)are proposed in this paper.Besides,the electric field,current distribution and theory of characteristic mode are used to design and analyze the antennas respectively.Firstly,ME dipole is widely used in broadband antenna due to its wide band and stable radiation characteristic.A dual-band linearly and circularly polarized(LP,CP)unidirectional hybrid antenna is proposed.The antenna is fed by an unbalanced single port,which simplifies the feed network and impedance matching.In the lower frequency band,a loop antenna operating in 1-? mode is formed to generate the LP radiation.In the higher frequency band,the1-? mode of the ME dipole antenna is excited to realize the wideband CP radiation.Compared to other 0.5-? mode ME dipole,the proposed antenna has a 3 d B axial ratio bandwidth(ARBW)of 4.10-6.60 GHz for the CP radiation.This antenna,for the first time,proposes a hybrid design of loop and ME dipole antennas with DBDP property excited by a single feeding port.And the proposed hybrid antenna has the advantage of high integration,thus is potentially suitable for multifunctional 2.45/5.2/5.8-GHz WLAN applications.Secondly,MTS antenna has the advantages of extending impedance matching,reducing profile and increasing gain.Based on this,a dual-band shared-aperture antenna with dualfunctional dual-layer MTS is proposed.The shared-aperture antenna consists of a double-slot antenna and a patch antenna,and by constructing the two antennas with orthogonal positions,dual-polarized dual-band(DPDB)performances are achieved with the MTS.In the lower band,0.5-? slot mode and TM leaky wave mode are excited,respectively.In the higher band,the MTS has a high dielectric constant and a gain enhancement of 6 d B for the patch antenna is obtained.Compared with the conventional Fabry-Perot(FP)cavity antennas,the distance between the dual-layer MTS and the patch antenna is decreased from ?/2 to 0.1 ?.Thus,with the simple multi-functional MS structure,the proposed MS antenna can be a good candidate in wireless-local-area networks(WLAN)systems.Finally,to achieve higher unidirectional gain and to explore the potential of improving the conformability of antenna based on MTS,a broadband MTS conformal antenna array is proposed.Theory of characteristic mode(TCM)is used for analysis and optimization of the proposed antenna element.Then,a parallel feeding network is designed to realize a wideband MTS antenna array composed of 4?8 antenna elements,and the conformal performance of the antenna array on a cylinder is studied and analyzed.The results show that the proposed conformal MTS antenna array can maintain a wide IMBW of 2.79-3.71 GHz.Stable high gain unidirectional radiation with the conformal angle of 0-10 degrees,with maximum gains is 21.6d Bi of 0 degree.Therefore,the proposed MTS antenna has the advantages of low profile,wideband and high gain,and is a good candidate of aircrafts,UAVs,and automobiles applications.