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 S 11 ≤ −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. INDEX TERMS Law cross polarization, differential feeding, wide band antenna, and hybrid antenna.

No abstract

The millimeter-wave (mm-wave) band is expected to be the optimal solution for future wireless communication systems as it provides a wide bandwidth, which enhancing data transmission rate. Therefore, high-directive antennas, principal elements for mm-wave wireless communications, are used at the mmwave band as they can overcome the negative effect of high path losses. A transmit-array antenna (TA) operates at the mm-wave band (around 28 GHz) with high aperture efficiency, high gain, wide bandwidth, and low-profile TA surface has been designed. Basically, the aperture efficiency of the TA depends on the unit cell (UC) characteristics, and feed antenna radiation pattern. Therefore, the UC elements designed based on capacitive differential feeding and true time delay techniques, as a result the designed UC has a wide bandwidth with a stable broadside radiation pattern, high cross-polarization discrimination and a full phase range (0-360 • ) and a maximum element loss of 0.5 dB. Moreover, the designed UC rotates the polarization of linearly polarized electromagnetic (EM) wave to its orthogonal direction with high efficiency, a polarization conversion ratio higher than 0.9 is achieved within the operating frequency band. The used techniques to design the proposed UC have a significant effect on TA antenna performance, in terms of gain and bandwidth. The TA antenna surface and the feeding antenna have been designed and fabricated. The maximum gain is 31.15 dBi. The 1 dB gain bandwidth is 12.7% while the 3 dB gain bandwidth is 21% around 28 GHz. The aperture efficiency is better than 50% and the cross-polarization level is less than -37 dB, on the frequency range from 25 to 31.5 GHz.