A 28 GHz Transmitarray Antenna With Enhanced Aperture Efficiency by Beam-Shaped Feed

The beam-shaped technique is introduced in the transmitarray antenna (TA) to enhance the antenna gain and aperture efficiency. Considering the path loss and the TA element’s pattern, the optimum radiation pattern of the feeding source is required to follow the $sec^{3}\theta $ in the radiated angular to enhance the illumination efficiency and vanish quickly out of the radiated angular to enhance the spillover efficiency. To realize the optimum pattern, a $2\times 2$ magneto-electric (ME) dipole antenna array is used as the basic structure to provide a proper gain with identical beamwidth in evaluation planes. Then, a superstrate loaded by airholes is placed above the array to mimic the optimum pattern. To validate this method, a prototype operating at 28 GHz is designed, fabricated, and measured. Measured results show that the prototype can achieve a peak gain of 29.1 dBi and peak aperture efficiency of 72.7%. The obtained 1- and 3-dB gain bandwidth is 11% and 25%, respectively. Since the prototype enjoys high aperture efficiency, low sidelobe levels, and simple structure, it is a promising candidate for future point-to-point wireless communication systems.