D-Band 4 × 4 Multi-Feed Array Antenna-in-Package for High-Power Combining and Polarization Synthesis.

A $4\times4$ multi-feed array antenna-in-package (AiP) is presented for high-power combinations and various polarization syntheses, which operates at D-band. The multi-feed antenna element was designed considering $N$ -number ( $K \times K$ ) of array antennas from the beginning. Consequently, the proposed antenna can provide four input ports while achieving an impedance bandwidth of 27%, port-to-port isolation higher than 10 dB, and cross-polarization discrimination (XPD) exceeding 20 dB. Moreover, power combination and polarization synthesis can be achieved using various excitation states. The $4\times4$ antenna array, according to simulated results, achieves a gain of up to 18.2 dBi, radiation efficiency of 81%, and XPD of over 20 dB. For verification purposes, the proposed antennas were designed with power dividers for different polarization states. An −10 dB impedance bandwidth of over 27% and a coverage of over ±60° were measured in the experiment.