A Hybrid Design Method for Thin-Panel Transmitarray Antennas

This paper presents a novel hybrid design technique to minimize the number of layers of the transmitarray (TA) panel while maintaining 360° phase shift range. Two types of unit cells, the receive-transmit unit cell and the frequency selective surface (FSS), are placed in the same aperture. The resulting TA panel is very thin but does not sacrifice the radiation efficiency of the array. The receive-transmit unit cell is an aperture-coupled square patch, and the FSS unit cell is a novel wide bandpass FSS. Both types of unit cells have three conductive layers and are printed on two substrates with a total thickness of 0.07λ0. The developed hybrid TA shows better gain than a homogeneous TA using the same elements. Meanwhile, it has comparable radiation performance but with a much lower profile compared to the conventional FSS-based TA designs that use several substrates separated by air layers. To verify the design concept, two hybrid TAs of different sizes with central frequency at 13.3 GHz were designed and fabricated. The measurements show that the TAs have at least 6.7% 1 dB gain bandwidth and higher than 30% aperture efficiency. Compared to the existing ultrathin designs of similar panel thickness, the presented TAs do not suffer from the phase quantization loss and achieve better or similar bandwidths.