A Ka-band 8-element 4-Beam Transmitter Front End with Hybrid VGA and Symmetrical Transformer-based Doherty PA

This paper presents a Ka-band transmitter front end in 65-nm CMOS for SATCOM. The proposed hybrid VGA achieves a 27-dB tuning range and 0.25-dB resolution, which is integrated with the active combing network to implement a compact multibeam structure. Low/high pass lumped delay lines are inserted between CS transistors and CG transistors to form I/Q generator for driving Gm-arrays from different phased beams. Besides, the output element adopts a symmetrical transformer-based Doherty power amplifier and analogy adaptive bias for improving the PBO efficiency with high PAPR modulation signal. This chip achieves a 19.2dBm Psat with channel efficiency of 20.5% and 18.2 dBm OP1dB. The measured maximum DE is 40.8% and 6-dB PBO DE is 28%. Compared with class-B/class-A PA, the DE is improved by 40%/180%. The proposed hybrid VGA achieves 0.26-dB/1.9° RMS gain/phase errors, respectively. The active phase shifter implements 6-bits 360 phase shifting with 0.25-dB/2.5° RMS gain/phase error.