| With the development of 5G/6G wireless communication systems,Millimeter-wave(MMW)/Terahertz(THz)applications have been extensively studied.The MMW/THz high frequency technology can realize the characteristics of wide bandwidth,high speed,low delay,and high integration.Meanwhile,it has a wide range of applications in medical,biological detection,remote sensing,security,and wireless communication.Due to the 60GHz frequency band is at the oxygen absorption peak,the signal can be attenuated quickly,therefore the 60GHz technology can be applied to short-distance high-speed wireless communications.Meanwhile,140GHz can be used in aerospace Communication because of low loss outside the atmosphere.Broadband MMW/THz antennas with high gain,high efficiency and small size will play an important role in various future applications.At the same time,circularly polarized(CP)antennas have the characteristics of anti-polarization mismatch and anti-multipath interference,which making the relative orientation between the transmitting and receiving antennas more flexible,and the quality of the link is better.As a result,CP antennas have become indispensable for wireless communication nowadays.Because the band of MMW and THz have the disadvantages of large transmission loss and poor penetration,the gain at the receiving side is too small.In order to increase the gain,a large-scale antenna array is usually used.However,as the area of the feed-network increases,the transmission loss also increases sharply.Eventually,even if the scale the antenna array is increased,the antenna gain cannot be increased.To solve this problem,this paper uses the feed-network based on high order cavity to reduce the loss and the size of the antenna.The research results of this paper include the following:1.60GHz high-gain circularly polarized antenna array based on TE340 mode substrate integrated cavity(SIC)Two broadband CP antenna arrays are proposed.The two antennas use the same feed-network.The first layer of the feed-network uses a high-order SIC based on the TE340 mode,and the second layer of the feed-network uses a traditional sequential rotating feed-network based on substrate integrated wave-guide(SIW).The difference between the two antennas is the radiating element.A circular patch with a pair of 45°-inclined slits is used as radiating element and a rectangular back-cavity is loaded in the first antenna.An improved magneto-electric(ME)dipole is introduced in the second antenna,which improving the radiation pattern.The measured results of the first antenna show that the-10-dB impedance bandwidth of 4×4 array is 27.2%,and 3-dB axial ratio(AR)bandwidth is 18.9%.The maximum gain is 19.3dBic at 62GHz,and the 3-dB gain bandwidth is 26.2%.The measured results of the second antenna show that-10-dB impedance bandwidth is 24%,and 3-dB AR bandwidth is 25.9%.The maximum gain is 19.4dBic at 62GHz.Due to their excellent performance,two antennas become one of the candidates for 60GHz short-distance communication.2.60 GHz high-gain circularly polarized antenna array based on high-order dual-mode SICA CP broadband antenna array based on high-order dual-mode SIC is designed.The overlap bandwidth of the impedance and AR can cover the band of 57 to 71 GHz.The first layer of the feed-network uses a dual-mode based on TE140 and TE410.The high-order dual-mode SIC not only achieves the effect of a power divider,but also achieves the effect of adjustable phase of output ports.The second layer feed-network adopts a flexible configuration to achieve sequential rotation technology,which uses a cross slot to excite the feed-network,and obtains a phase difference by adjusting the length difference of cross slot.In this way,the feed-network can provide the required phase difference without adding any additional quarter-wavelength lines.This structure uses aperture coupling between layers,which is suitable for processing and manufacturing for MMW.A circular patch with a pair of 45°-inclined slits and a rectangular back-cavity are use as radiating element.Compared with the circular back-cavity,rectangular back-cavity can effectively increase the gain of the antenna.After processing and measuring,the-10-dB impedance bandwidth of the 4×4 antenna array is 23.8%,and the 3-dB AR bandwidth is 24.6%.The maximum gain is 20.8 dBic at 67GHz.During the 57-72.5 GHz band,the gain is bigger than 17.5dBi,and the maximum aperture efficiency is 79.6%.3.140GHz circularly polarized antenna array based on hexagonal SICA CP 8×8 antenna array based on feed-network with hexagonal SIC using LTCC processing technology is proposed.The first layer of feed-network adopts a one-to-four power divider based on a hexagonal SIC.Compared with the traditional feed-network with the fundamental mode,this structure is simple in design and small in size,which reduces the complexity and loss of the feed-network.The impedance performance of the antenna is improved by loading the matching posts in the hexagonal SIC.Both the second and third layers of feed-networks use SIW-based sequential rotating networks.This configuration can expand the AR bandwidth and improve the purity of the CP.The simulated results of designed 8×8 antenna array shown that the-10-dB impedance bandwidth is 22.6%,and the 3-dB AR bandwidth is 20%.The maximum gain is 19.7dBic,and the gain bandwidth of 3-dB is 11.8%.The side lobe level of the antenna array is less than-13dB. |
