Research On Circularly Polarized Antennas Utilizing Spoof Surface Plasmon Polaritons

With the rapid development of the wireless communication systems,high performance microwave devices have attracted much attention.Antennas,which play the role of transmitting and receiving electromagnetic waves,are indispensable for communication systems.Among them,Circularly-Polarized(CP)antennas have obtained increasing attention due to their attractive characteristics of reducing multipath interferences and suppressing polarization mismatching.On the other hand,Spoof Surface Plasmon Polaritons(SSPPs)waveguide is a special kind of surface wave transmission line,which have been widely employed in the design of antennas and microwave devices,fulfilling the communication devices.To expand the SSPPs further in antenna aera,this thesis will focus on the co-design of SSPPs and CP antennas.The research results of the thesis can be summarized as follows: 1.A low profile wideband CP dipole array antenna is analyzed and designed.Firstly,a parallel transmission line-based feeding network was employed to excite four width-stepped dipoles.In order to expand the impedance bandwidth and 3-d B axial-ratio bandwidth,four parasitic metallic loops and four long strips are introduced around the antenna.Furthermore,an AMC reflector is utilized to reduce the profile of the CP antenna.Finally,the antenna is fabricated and measured,and the tested results show that a 10-d B impendence bandwidth of 42%(1.82 to 2.8 GHz)and 3 d B ARBW of 36.4%(1.89 to 2.73 GHz)are achieved,respectively.Moreover,the designed antenna realized a low profile of 0.13 ?(? is the free-space wavelength at the center frequency)and a gain of average 9.5 d Bi with less than 1.5 d B variation within the 3 d B AR bandwidth.2.Based on the slow wave effect of the SSPPs,we designed a novel CP antenna without extra phase shifter.The designed antenna contains a SSPPs-based power divider and four tightly coupled dipoles.The power divider is designed based on the bilayer SSPPs transmission line,aiming to excite four dipoles with equal amplitude and orthogonal phase.To obtain a compact size,dipoles are tightly coupled by introducing several coupling strips.At last,the designed antenna can realize CP radiation without the extra delay lines,simplifying the design of CP dipole array antennas.3.Based on the single layer SSPPs transmission line,a shared-aperture dual-CP antenna is designed and investigated.The antenna consists of two pairs of dipoles,one of which is fed by slow-wave feedlines and the other is fed by coplanar striplines(CPS).The CP operation is realized by exciting four orthogonally placed dipoles with orthogonal electric current.Furthermore,the dual-CP working statement is achieved via employing a couple of orthogonally placed differentially-fed baluns between the antenna and ground.Moreover,in order to analyzing the port coupling principle of this antenna,an equivalent model is proposed on the basis of forward current and backward current.Subsequently,four parasitic loops are introduced,aiming to obtain high isolation over a wide operation band.Finally,a novel dual-CP antenna with high port isolation is designed based on the slow wave effect of SSPPs.