Stability & Biasing in mmWave GaAs/GaN PAs: Challenges and Solutions

Abstract: Millimeter-wave (mmWave) power amplifiers (PAs) are critical building blocks in next-generation radar, satellite, defense, and 6G communication systems, where output power, bandwidth, and efficiency must be achieved under stringent size, weight, and power (SWaP) constraints. Among the enabling technologies, Gallium Arsenide (GaAs) and Gallium Nitride (GaN) continue to dominate due to their complementary strengths in linearity, noise performance, and high-power density.

This talk will focus on design considerations unique to mmWave GaAs and GaN PAs, with particular emphasis on stability and biasing challenges at frequencies above 20 GHz. Unlike lower microwave designs, mmWave PAs are highly susceptible to low-frequency oscillations, odd-mode instabilities, and bias-induced resonances. To mitigate these, stability networks—ranging from RC shunt loading and resistive feedback to series loading and quarter-wave stabilization—must be co-optimized with matching and biasing schemes. Special attention will be given to the integration of stability networks with bias networks, where parasitics from bias chokes, decoupling capacitors, and high-impedance bias lines can introduce additional poles/zeros in the response, affecting both gain flatness and unconditional stability.

The presentation will review practical approaches to stabilizing mmWave PAs without compromising efficiency or bandwidth, including the use of lossy transmission lines, broadband bias tees, and RC filtering strategies tailored for GaAs vs. GaN processes. Case studies will illustrate how bias network design impacts stability margins and overall PA performance, and how distributed versus lumped stabilization choices evolve with frequency. The session will conclude with a discussion of packaging and integration considerations, where bondwire inductances, via transitions, and LTCC/SiP bias routing play a defining role in amplifier stability at mmWave frequencies. 

Speaker's Bio

Dr. Asmita Dani is an RF and mmWave technologist specializing in GaAs and GaN millimeter-wave IC design for aerospace, defense, automotive, wireless, and quantum applications. She holds a Ph.D. in Electrical Engineering from the University of Colorado Boulder and brings over a decade of experience in RFIC, MMIC, and high-power RF design.

Her career spans leading roles at both large scale companies and startups such as Metawave, Rigetti Computing & Reach Labs., where she advanced technologies in beamforming radar, wireless power, quantum IC packaging, and broadband PAs/LNAs across Ka, E, and D bands. Currently, she offers freelance consulting in advanced mmWave amplifiers and front-end design.

Asmita is an IEEE member and reviewer, with 10 US and international patents and 6 international publications in RF technology. She has also obtained certification in the Stanford University’s Idea to Market (I2M) program, combining deep technical expertise with product strategy and vendor/foundry management experience.

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