Broadband Transmitarray Antenna Design Using Polarization-Insensitive Frequency Selective Surfaces

Applications of frequency selective surfaces (FSSs) for transmitarray antennas (TAs) are investigated. Two broadband polarization-insensitive FSS elements are proposed and their transmission performances are evaluated against the desired amplitude and phase responses for this application. Accordingly, two small aperture (20 cm × 20 cm) broadband TAs are designed and their radiation characteristics are compared to each other. The simulated results show a maximum aperture efficiency of (38.4% and 36.7%), -1 and -2 dB gain bandwidths of (13.5% and 11.8%) and (16.08% and 19.75%) for the first and second TA, respectively. The antenna with superior performances is successfully fabricated and tested as a proof of concept. The measured maximum aperture efficiency of this TA is 34.64% and its -1 and -2 dB gain bandwidths are 10.2% and 14.83%, respectively. Moreover, the scanning performance of this antenna is also investigated by changing the feed location and it is shown that reasonable results in terms of sidelobe levels (less than -15 dB), appearance of shoulder and coma lobes, and gain loss (better than -3 dB) are achieved for scanning range up to ±35° in both Eand H-planes. In addition, a new low-cost cavity-backed folded dipole antenna (CBFDA) is also proposed as a feed for TAs in this work. The introduced feed offers the required radiation pattern to illuminate the designed FSSs.