Research On Broadband Differential Low Cross-polarization Antennas

As an important device for transmitting and receiving radio waves,the performance of the antenna greatly affects the intensity and quality of the signal.With the rapid development of wireless communication technology,the demand for fully integrated RF circuit front-end products is expanding.The front-end of the RF circuit is mostly realized by differential technology,but most antennas are currently designed with single-port and cannot be directly connected to the differential RF front-end products.The differential antennas change the traditional design method.They can be directly fed by differential signals,which avoid the use of balun and other conversion elements.By using differential antenna not only improves the system integration,but also reduces unnecessary front-end losses and then improves the system efficiency.In addition,differential antennas also have the advantages of high isolation,low cross-polarization,and high CMRR,which have been paid the more and more attention.Based on the traditional theory of the differential antennas,this paper studies two types of wideband,low cross-polarized differential antennas.The main contents are summarized as follows:Firstly,a 4 × 4 wideband microstrip antenna array differentially fed by the waveguide power dividers is proposed.Two T-shaped resonators are used to differentially feed a rectangular patch,which increases the resonant points of the antenna and results in a wide impedance bandwidth.Differential feeding effectively reduces the cross polarization of the antenna and forms a stable pattern.A 4 × 4 array antenna is formed with a distance of a wavelength in the H-plane and 0.8 wavelength in the E-plane.For the convenience of the test,eight waveguide E-plane power dividers and three-stage waveguide H-plane power dividers are installed below the 4 × 4 antenna array.The power divider and the 4 × 4 antenna array are connected by coaxial probes.Finally,the antenna array prototype operating at the centra frequency of 28 GHz is designed and fabricated.The 3d B gain bandwidth of the antenna is10.7%,and the peak gain is 19.54 d B.The gain of the antenna is more than 18 d B over the-10 d B frequency coverage range from 26.5 GHz to 29.5 GHz.The cross polarization of the Eplane and H-plane are both below-26 d B.Secondly,a wideband differentially fed Fabry-Perot resonator antenna is proposed.The antenna uses a Fabry-Perot cavity structure,which ensures the high gain characteristics.In order to guarantee a wide impedence bandwidth,rectangular strips are loaded on both sides of the rectangular patch and air substrate is also used in the primary feed.The differential feeding adopted in the primary feed effectively reduces the cross polarization of the entire antenna.For the convenience of the test,a waveguide E-plane power divider is installed below the antenna,and two semi-flexible RG402 coaxial lines are connected to the feeding source.Finally,a FabryPerot resonator antenna working at 5.5 GHz is designed and processed.The 3d B gain bandwidth of the antenna is 18.4%,and the peak gain is 11.06 d B.The gain of the antenna is above 10 d B over the-10 d B impedance bandwidth from 5.19 GHz-6.2 GHz.The cross polarization of the E-plane and H-plane are both below-30 d B.,and the aperture efficiency of the antenna is 45%.