| Periodic structures are widely used in antenna design.As a kind of periodic structure with strong field confinement for electromagnetic wave,spoof surface plasmon polaritons(SSPPs)have a strong advantage in the design of traveling wave antennas and flexible antennas due to their rich dispersion relation and conformal transmission ability.Based on the theory of SSPPs and substrate integrated waveguide(SIW),this thesis researchs and designs an endfire antenna based on odd mode SSPPs,a millimeter-wave SSPPs endfire antenna and a planar endfire circularly polarized antenna based on SIW.(1).The design principle of endfire antenna based on SSPPs is studied.The endefire conditions for the SSPPs antennas are analyzed and deduced.Firstly,for the asymmetric SSPPs antenna,the number of SSPPs units is determined by the equivalent electric fields on both sides of the SSPPs.Meanwhile,for the symmetric SSPPs antenna,the differential feeding is determined to be the premise of the endfire,and then the number of SSPPs units is calculated by the Hansen-Woodyard condition to achieve the maximum endfire directivity.(2).An endfire antenna based on odd-mode SSPPs is designed.A pair of symmetrical SSPPs transmission lines are fed by a differential feeding structure to excite the odd-mode SSPPs,and the number of SSPPs elements is determined by the maximum endfire directivity.At the same time,a gradual SSPPs is introduced at the end to match the phase between the antenna and the free space,which can improve the radiation efficiency of the antenna.The designed SSPPs antenna achieves good endfire radiation in the frequency range from 9 GHz to 11 GHz,and its average gain is 11.5 d Bi.Besides,the antenna has the advantages of small size,high gain,high aperture efficiency,wide band and good directionality.(3).A flexible millimeter wave endfire antenna based on SSPPs is designed.The implementation of the flexible antenna is verified on an ultra-thin substrate by using the intrinsic property of strong field confinement of SSPPs.In order to realize endfire radiation,a differential feeding structure is used to feed the symmetrical SSPPs transmission line,so that the tangential electric fields on both sides of SSPPs are in-phase and they can be superimposed at endfire direction,so as to achieve strong endfire radiation.Finally,the designed antenna operates from 30 GHz to 50 GHz,and the average gain in the frequency band is 14.9 d Bi in the plane state.When the bending angle of the antenna increases from 0° to 30°,the impedance characteristics and return loss of the antenna remain unchanged,and the gain variation is stable within 2.7 d Bi.The measured results are in good agreement with the simulation results,indicating that the antenna has good flexibility characteristics and has strong application potential in flexible circuits in the future.(4).In order to solve the problem of large size of the endfire circularly polarized antenna,a compac planar endfire circularly polarized antenna is designed.The vertical polarization radiation of energy is realized by periodically etching symmetrical rectangular slots on the upper and lower walls of SIW,and a Vivaldi antenna is loaded at its end to provide horizontal polarization.Then,the radiation efficiencies of the orthogonal polarizations are adjusted to ensure that the energy radiated by they are equal,and the distance between the orthogonal polarizations is adjusted to ensure the phase difference close to 90°.Finally,a planar circularly polarized endfire antenna is achieved with an average gain of 10.1 d Bi operating from 24.4 GHz to 25.8 GHz.This antenna has the characteristics of narrow beam,high gain,wide band and small aperture. |
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