A K -Band Four-Beam Transmitter With Decoupled Phase/Gain Control and Enhanced Power Back Off Efficiency for SATCOM

This article presents a 17.720.2 GHz eight-element four-beam RF-beamforming transmitter in 65-nm CMOS for satellite communication (SATCOM). The transmitter utilizes an analog scheme in the variable-gain amplifier (VGA) to achieve dB-in-linear gain control with a high dynamic range (DR), together with a current combining crossbar for a compact footprint. The vector-modulation-based (VM-based) phase shifter (PS) adopts the cancellation-based <tex-math notation="LaTeX">Gₘ</tex-math> units for low switching variation. Furthermore, eight PSs of each beam are split into two groups, with each group sharing the same tunable I/Q generator for low power consumption. Considering the increased peak-to-average power ratio (PAPR) caused by high-order modulation schemes and multibeam operation, the transmitter incorporates compact transformer-based Doherty power amplifiers (DPAs) with adaptive bias control to improve the power efficiency at back-off. The chip achieves a 31-dB gain-tuning range with a 0.283-dB step and a 360 <tex-math notation="LaTeX">∘</tex-math> phase-shifting range with a calibrated 7-bit resolution. The measured root-mean-square (RMS) phase/gain errors induced by the VGA/PS are below 2.05 <tex-math notation="LaTeX">∘</tex-math> /0.147 dB, respectively, which decouples phase/gain control. The transmitter achieves a maximum output 1-dB gain compression point (OP <tex-math notation="LaTeX">1 dB</tex-math> ) of 17.9 dBm and a maximum saturated power ( <tex-math notation="LaTeX">Pₛₐₜ</tex-math> ) of 18.9 dBm. The output element exhibits 29.3% drain efficiency (DE) at 6-dB power back off (PBO) from <tex-math notation="LaTeX">Pₛₐₜ</tex-math> , which is 1.56/3.12 times over the normalized class-B/class-A implementations, demonstrating Doherty PBO efficiency enhancement. The chip occupies an area of 8.59 <tex-math notation="LaTeX">×</tex-math> 4.17 mm <tex-math notation="LaTeX">²</tex-math> and consumes 398 mW per element at OP <tex-math notation="LaTeX">1~dB</tex-math> . Additionally, a 16-element linear array has been developed to showcase the capabilities of the multibeam operation and gain tapering.