Integrated Broadband Circularly Polarized Multibeam Antennas Using Berry-Phase Transmit-Arrays for $Ka$ -Band Applications

In this article, integrated millimeter-wave (mmW) broadband circularly polarized (CP) single-beam/multibeam antennas (MBAs) are reported. The antennas comprised a Berryphase (BP) transmit-array (TA) containing three layers of slotted elliptical metallic resonator arrays and a cluster of substrate integrated waveguide (SIW) -fed CP source radiators with an anisotropic impedance surface (AIS) superstrate. By utilizing broadband mmW CP radiators, BP-based transmission phase compensation, and tailoring the dispersive transfer function of the TA cell, broadband CP high-gain beams can be generated with improved gain flatness and an antenna profile of only 2.6λ 0 . Moreover, by employing multifocal strategies in the design of TAs, the scanning loss for the multifeed MBAs can be alleviated, expanding their range of coverage. Two Ka-band prototypes were fabricated and characterized. The single-feed single-beam antenna experimentally achieves a peak gain of 22.6 dBic and a 2 dB gain bandwidth of 20.7%, within which the S 11 is below -10 dB and axial ratio (AR) is smaller than 3 dB. The second prototype, which contains five source radiators and a bifocal TA, generates five pencil beams that cover a range between ±33°. It features a peak broadside gain of 22.2 dBic, a joint AR <; 3 dB, and a 2 dB gain bandwidth of around 17.7%. The scanning loss and beam squinting are smaller than 1.2 dB and 1.7°, respectively. Within this band, the S 11 is below -10 dB and mutual coupling is smaller than -20 dB. Finally, the numerical simulation of a broadband CP 21-beam antenna with a quad-focal TA is shown, which provides a 2-D coverage of 32° cone. The demonstrated single-beam antenna/MBA can be promising candidates for various mmW applications, such as satellite and fifth-generation (5G) communications.