Research On Millimeter-Wave/Teraherz Circularly Polarized Antenna And Array

Recently,millimeter-wave(MMW)and terahertz(THz)in the electromagnetic wave spectrum have attracted significant interest in science and engineering.Advantages of large bandwidth and small wavelength have opened up opportunities for MMW/THz applications such as fast/ultra-fast wireless communication and miniaturized highresolution imaging radar.Antennas are one of the critical components for the deployment of these wireless systems.Meanwhile,wireless systems with circularly polarized(CP)antenna can provide more promising channel performance compared with those using linearly polarized antenna,because circular polarization can reduce polarization mismatch and suppress multipath interferences.Due to high operation frequencies and large bandwidths,the design of MMW/THz CP antenna faces many challenges,and has become the focus in academia and industry.The main focuses of this dissertation including the implementation of crossed dipoles in MMW frequency band,the design of high-performance MMW CP antennas,and design method of THz CP antenna array.The main innovative contributions of this dissertation are summarized as follows:1.A method of implementing crossed dipoles in Ka-band is proposed.To deal with the feeding issues of crossed dipoles in MMW frequency band,a detached form is proposed for the first time,which integrates a transition and the crossed dipoles on the same substrate.Meanwhile,the crossed dipoles are backed by a ridged cylindrical cavity for better radiation performances as well as for robustness.The CP radiation mechanism is investigated.Measured results show that the proposed cavity-backed CP crossed dipoles can achieve 3-dB axis ratio(AR)bandwidth of 30.7%,maximum gain of 13.9 dBi,and stable radiation patterns in the whole operation frequency band.2.A novel method to design CP antenna with wide 3-dB AR beamwidth is proposed.The radiation aperture is chosen as open-ended waveguide cavity(OEWC).Therefore,the distributions of the two orthogonal modes on the aperture will determine the far-field CP properties.The influences of the dimensions of the OEWC aperture,the amplitude ratio and phase difference of the two orthogonal modes on the 3-dB AR beamwidth are investigated.Finally,the OEWC antenna is designed,fabricated,and measured in 60 GHz frequency band.The crossed dipoles are chosen as the exciter of the OEWC,which is coupling-fed by a transverse slot on the top metal surface of the substrate integrated waveguide.Experimental results show that the proposed antenna can achieve 3-dB AR beamwidths of 134 o and 174 o at 60 GHz on the XZ and YZ planes,respectively.3.A novel antenna constructed by an elliptical cavity and a dipole exciter to realize CP radiation with wide AR bandwidth is proposed.The dipole exciter is put by a specific angle relative to the major axis of the elliptical cavity,and it can excite two orthogonal electric field components.With the optimization of included angle,the height of the dipole and the dimensions of the cavity,the two orthogonal modes with equal magnitude and 90 o phase difference in the antenna aperture can be achieved,and then antenna present a CP radiation.The antenna is designed,fabricated and measured in MMW frequency band.Experimental results show that in the frequency band from 50 to 62.8 GHz,the AR is kept below 3dB.4.A novel 60 GHz antenna composed of a patch dipole and a slot dipole for CP radiation is proposed.The patch dipole is coupled-fed by a T shaped strip,and the slot is differentially fed by two strips connected to the two arms of the dipole.Meanwhile,to restrain the surface wave and enhance the radiation efficiency,a cavity consisted of metallized through holes is added.The antenna is realized on a single printed circuit board with the advantages of low cost and easy integration.Experimental results show that its available 3-d B AR bandwidth is from 56.2 to 65 GHz,in which the S11 is kept below-10 dB,and the stable radiation patterns have been achieved.5.A CP leaky-wave antenna with high gain is proposed.The leaky waves are realized by the metallic strip gratings printed on a ground dielectric slab.To achieve CP radiation,the optimized structure of the antenna is an Archimedean spiral.It is center-fed by a monopole probe and no extra feeding network is required.The proposed antenna is designed,fabricated,and measured in 60 GHz band.Experimental results show that the antenna gain goes up to 24.52 dBi at 60.5 GHz.6.Two new THz patch arrays with relatively high gain for CP radiation are investigated.The first THz array is fed by sproof planar plasmonic waveguide(SPPW)of metallic blind-hole array.The radiation element is an inclined rectangular patch coupled-fed by the SPPW,and the series-fed array can achieve frequency-scanning CP radiaton.The second THz array is planner patch array fed by insert dielectric waveguide(IDW).The array element is hybrid patch element consisting of a rectangular patch and a circular patch distributed on the two sides of the IDW aperture.The parallel-series feeding network is composed of a 4-way power divider and four IDWs.According to the Silicon micromachining technology,the THz CP array is designed at 300 GHz.Simulated results show that in the frequency band from 296 to 304 GHz,the AR is kept below 3 dB and the average radiaton efficiency is 34.3%.The antenna gain is 17.14 dBi at 300 GHz.