A Ka-Band Four-Beam High-Linearity Transmitter With Beam Interference Cancellation for SATCOM Multibeam Communication

Abstract

This article presents a 27.7–31.2-GHz highly integrated eight-element, four-beam transmitter front end in 65-nm CMOS for phased-array multibeam communication. To eliminate beam interference in multibeam coherent communication, an interference cancellation scheme is introduced within the multibeam transmitter. In the circuit design, the proposed hybrid variable-gain amplifiers (VGAs) combine digital common-source (CS) VGAs and analog Gilbert-cell-based VGAs to achieve both a large dynamic range and high resolution. The hybrid VGAs are then embedded into a transmission-line-based network, forming a compact $4\times 4$ beam combining structure. To support multibeam phase steering, four pairs of Gm arrays interpolate four individual phase sates from the same I/Q signals generated by low- and high-pass lumped delay lines. These delay lines are inserted between CS transistors and common-gate (CG) transistors to isolate the impedance fluctuates of magnetic coupling resonance load across frequency. To manage the high peak-to-average power ratio (PAPR) modulation signal, the output stage employs a symmetrical transformer-based Doherty load modulation network and an analog adaptive gain control in the auxiliary path to improve the power-back-off (PBO) efficiency. With a 1.1-V supply voltage, this transmitter achieves a saturated output power (Psat) of 19.2 dBm with a 20.5% channel efficiency (CE) and an output power 1-dB compression point (OP1dB) of 18.2 dBm. The measured maximum drain efficiency (DE) is 40.8%, while the 6-dB PBO DE is 28%, indicating improvements of 40%/180% compared to the normalized class-B/A implementations. The proposed hybrid VGA achieves a 27-dB tuning range and a 0.25-dB gain step with 0.26-dB/1.9° root mean square (rms) gain/phase errors, while the phase shifter (PS) implements 6-bit, 360° phase shifting with 0.25-dB/2.5° rms gain/phase errors, enabling precise gain tapering and beam steering.