A 37.5 to 42.5 GHz Broadband SiGe Analog Linearizer RFIC for Q- Band Satellite Power Amplifier Linearization

This work presents a compact broadband analog linearizer RF integrated circuit (LRFIC) for Q band satellite payloads, designed in IHP 130 nm SiGe BiCMOS technology and covering 37.5–42.5 GHz. The proposed LRFIC realizes a split path predistortion architecture: a linear branch (LB) forwards and amplifies the carrier with minimal distortion using a tunable true time delay, a fixed delay line for group delay alignment, and a fixed gain amplifier, while a nonlinear branch (NLB) generates controllable third order intermodulation (IM3) products using an IM3 generator followed by a vector modulator (gain control 0–15 dB and 360° phase shift range), a tunable phase equalizer and a fixed gain amplifier.
LB and NLB are recombined with a Wilkinson combiner and a variable gain output stage, providing 0 to +5 dBm output for a −20 dBm input. All subblocks were designed and validated for high linearity that only the intended IM3 content is produced in the NLB. The principal novelty is the full on chip integration of the predistortion chain and an adaptive self calibration (CAL) capability that adjusts IM3 to carrier ratio, amplitude, phase and group delay to predistortion both traveling wave tube amplifiers and solid state power amplifiers.
Achieving the inverse IM3 predistortion at the high-power amplifiers (HPA) input requires an extensive control of the LRFIC allowing the system to adapt to various HPA and dynamic operating conditions.
Detailed simulations and ongoing measurements support the concept; experimental results indicate adaptive IM3 tuning across the targeted frequency band while preserving carrier integrity and show that generated IM3 tones can be suppressed to levels comparable with inherent IM5 products under the tested conditions. Future work will finalize the CAL implementation and quantify system performance under realistic payload conditions. The integrated LRFIC reduces payload complexity and enables in system linearization for CubeSat RF frontends.