Wideband Transmit Arrays Based on Anisotropic Impedance Surfaces for Circularly Polarized Single-Feed Multibeam Generation in the Q-Band

In this article, a class of wideband transmit arrays (TAs), composed of cascaded anisotropic impedance surfaces (AISs), for circularly polarized (CP) multibeam generation from a single feed horn are reported. The dispersionless phase compensation is achieved by the Berry phase (BP) via imposing a spatially dependent rotation angle on the TA unit cells. A homogenized model for the BPTA unit cell is proposed and utilized for obtaining a wideband response by tailoring the dispersive properties of the AIS layers. Two modeling methods, an analytical vectorial field analysis and a full-wave strategy incorporating the homogenized model, were employed to efficiently evaluate the performance of the BPTAs. In order to validate the proposed unit cell and the modeling methodologies, a Q-band single-beam BPTA is demonstrated, which achieves a peak gain of 30.2 dBi and a 1 dB bandwidth of 11.1 within which the axial ratio is smaller than 2 dB. Furthermore, by employing the intersection approach for pattern synthesis, several Q-band BPTAs supporting multiple concurrent symmetric/asymmetric CP pencil beams and circular-shaped flat-top beams are designed. A BPTA prototype for producing quad CP pencil beams with unequal gain values was fabricated and characterized, yielding good performance with an overall operational bandwidth of about 11. The proposed BPTAs are promising candidates for point-to-multipoint communication and point-to-multiregional coverage in wideband millimeter-wave communications for wireless and satellite applications.