Ultra-Wideband Differential Fed Hybrid Antenna With High-Cross Polarization Discrimination for Millimeter Wave Applications

A wideband differential fed patch antenna with high cross-polarization discrimination is proposed at mm-wave range. For the purpose of increasing antenna bandwidth, capacitive coupling technique is used. Also, the differential feeding is utilized to ensure broadside radiation and low cross-polarization. The designed antenna has an ultra-wide bandwidth of 55% around 30 GHz with S11 ≤ -10 dB, and a peak gain of 8 dBi. The radiation pattern has a cross polarization level less than -20 dB over the operating frequency band. The differential feeding technique depends on equal power division and 180° phase difference for all the antenna bandwidth. Due to the wide bandwidth of the differential feeding antenna element, two designs of the feeding circuits (which include rat race and probe strip line transition) are used to cover the whole frequency band of the antenna. A gain enhancement has been achieved by adding a horn to the designed antenna with an efficient aperture efficiency. The designed antennas have fractional bandwidths of 28.73% (at center frequency 25.64GHz) and 26.3% (at the center frequency 32.2 GHz), for the lower and the upper bandwidths, respectively. An average gain of 14.5 dBi has been achieved for the frequency band from 21.8 GHz to 36.5 GHz. The antenna performance is verified through fabrication and measurement, where the simulated and measured results are in a good agreement.