This article presents a scalable Ka-band phased array transmitter designed for the upload channel of terrestrial mobile transceivers in satellite communications (SATCOM, 27.5–30.0 GHz). The transmitter consists of a 16-channel active phased array system with digitally switchable circular polarization, enabling seamless alternation between right-hand (RHCP) and left-hand circular polarization (LHCP). A linearly polarized patch antenna is utilized, achieving circular polarization through the sequential rotation technique. By integrating the radiating element within a modular multilayer printed circuit board (PCB) and employing a superheterodyne architecture, the system supports full digital beamforming in a compact, scalable design. The array achieves a scan range of ±50° with a scan loss of approximately 2 dB in both principal planes ( $arphi = 0^{circ }$ and $arphi = 90^{circ }$ ) and maintains a roll-off factor ${cos}^{1.03}( heta)$ . The operational bandwidth of 15.4% (26.99 - 31.49 GHz) is accompanied by an axial ratio with great polarization purity across the scanning range. These features, combined with a thermal management strategy, highlight the system’s innovation as a high-performance, adaptable solution for next-generation SATCOM applications.