Research On Millimeter-wave Antennas Fed By Transmission Lines With Periodic Structures

Millimeter-wave frequencies has been playing a crucial role in the advanced wireless communication applications due to the sufficient spectrum resources.As the indispensable devices in the millimeter-wave communication systems,millimeter-wave antennas and arrays have become the frontiers and hotspots in the fields of antenna research in recent years.Periodic structures are essential methods to realize electromagnetic field and wave modulation,which have been widely applied into the research of antenna and transmission lines.As two kinds of typical transmission lines with periodic structures,spoof surface plasmon polaritons（SSPPs）and substrate-integrated gap waveguide（SIGW）have critical application value in the research of millimeter-wave antennas.However,the SSPPs-based feed methods for antennas and arrays are relatively single,which makes these kinds of antennas difficult to realize broadband fixed radiation beams,multibeam and multi-polarization radiation beams required for the millimeter-wave applications.On the other hand,most of the millimeter-wave SIGW-fed antennas and arrays are designed based on the two-dimensional planar integrated method with low utilization rate of the vertical dimension in integrated space,the realization of 3D integrated designs is still difficult.In order to overcome the above issues,the millimeter-wave antennas fed by SSPPs and SIGW are investigated in this paper,methods of mode excitation,polarization modulation and fixed and multi beam radiation of the SSPPs-fed antennas and arrays are proposed in millimeter-wave band,as well as the method of 3D integration for millimeter-wave antennas based on vertical SIGWs.The research results provide theoretical and technical support for the design of millimeter-wave antennas in the applications of new-generation wireless communication.The main innovations of this paper are as follows:1.The design method of millimeter-wave SSPPs-fed patch antennas is proposed.The mechanism of radiating mode excitation for the SSPPs-based patch antenna is defined,the methods of proximity coupling feed and direct feed are proposed for the antennas.The designed antenna with a profile of 0.06λ₀ obtained a bandwidth of 8.2%and stable fixed radiation beams with the gain around 6 d Bi.To conquer the deficiency that high cross polarization in H-plane of the SSPPs-fed patch antenna,the method of cross polarization suppression is further proposed by adding two slits on the ground of the patch antenna,by this means,the cross polarization of the antenna can be reduced to lower than-15 d B.To fulfill the requirement of multi-polarized radiation patterns of antennas for millimeter-wave wireless communication applications,the method of polarization modulation for SSPPs-fed patch antennas is proposed.An impedance bandwidth of 15.9%,a 3d B AR bandwidth of 7%and a gain around 5.6 d Bi are obtained by the designed circularly-polarized antenna.An overlapped impedance bandwidth of 13.7%,an isolation of more than 15 d B between the two inputs,and stable dual-polarized radiation patterns across the operating band are obtained by the designed dual-polarized antenna.2.The design methods of millimeter-wave SSPPs-based feed network and SSPPs-based antenna array with fixed radiation beams are proposed.The structure and design method of the millimeter-wave Y-shaped power divider with equal power dividing ratio based on the single-side SSPPs is proposed,moreover,the 1-to-4 parallel feed network is further realized based on the above design.The structure and design method of the millimeter-wave power divider with adjustable power dividing ratio based on the double-side SSPPs is proposed,after that,the series feed network with compact geometry is fulfilled.By combing the 1-to-4 parallel feed network with the proposed single-polarized patch antenna,a millimeter-wave SSPPs-fed patch antenna array with fixed radiation beams is realized.The antenna array has a measured bandwidth of 13%,a gain up to 12.8 d Bi,and stable radiation patterns over the operating band.With utilizing two 1-to-4 series feed networks to excite the proposed dual-polarized patch antenna,a SSPPs fed dual-polarized patch antenna array is fulfilled.The antenna array has an overlapped bandwidth of 15.4%,the gain results at center frequency are 8 and 8.6 d Bi with two polarizations excited respectively.3.The design methods of millimeter-wave SSPPs-based Butler matrix and multibeam array antenna are proposed.The structure and design methods of beamforming functional devices based on the double-side SSPPs are proposed,involving the 3 d B coupler,crossover,and phase shifters.A 4×4 SSPPs-based Butler matrix with a modified geometry is fulfilled by connecting the proposed components together.By using the proposed beamforming network to excite the patch antenna array,a bandwidth of 15%and four stable radiation beams with gain results from 10.5 to 12 d Bi are obtained.The beams can cover an azimuthal range of±30°,the isolations between the inputs of the antenna are more than 25 d B.4.The design method of millimeter-wave 3D SIGW-fed dual-polarized horn antenna is proposed.The vertical SIGW transmission structure that integrated into multi-layered stacked substrates is proposed,and the propagation features of the proposed vertical SIGW are investigated.An interconnection is designed between the vertical and horizontal SIGWs to realize efficient energy transmission between different substrate layers.Based on that,by combing the vertical and planar SIGWs,a fully 3D substrate-integrated orthomode transducer（OMT）and dual-polarized horn antenna are fulfilled,which realizes millimeter-wave substrate-integrated design for the devices with 3D geometry.The 3D SIGW-based OMT-fed horn antenna has an impedance bandwidth of30%,the isolation between the inputs is more than 45 d B over the operating band,the maximum gain results are 10.3 and 11.7 d Bi for the vertical and horizontal polarizations.