Residual AM and PM Noise of Selected X-Band Amplifiers

Published

October 2, 2026

Author(s)

Archita Hati, Craig Nelson, Scott Littrell

Abstract

In microwave systems design, amplitude modulation (AM) noise is often ignored relative to phase modulation (PM) noise. However, in high-performance applications requiring ultra-low PM noise, AM noise becomes a critical limiting factor due to AM-to-PM conversion mechanisms. Because AM noise specifications are rarely, if ever, provided for commercial microwave components, this study characterizes the residual AM and PM noise of several 10 GHz amplifiers. We present performance data for various Heterojunction Bipolar Transistor (HBT) amplifier designs and demonstrate the noise reduction achieved through power-summed configurations. For example, a discrete-die GaAs HBT amplifier (labeled GA-HBT-1) achieves residual PM noise below −160 dBrad2/Hz and AM noise of approximately −155 dB/Hz at a 1 kHz offset in a quad power-summed configuration. A notable finding is that the majority of amplifier designs surveyed in this study exhibit higher AM noise relative to their PM noise, with only a few exceptions. The impact of bias supply quality on residual noise is also quantified, demonstrating that the choice of voltage regulator is a first-order design parameter below 1 kHz offset.

Citation

arXiv https://arxiv.org/pdf/2610.03178

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https://doi.org/10.48550/arXiv.2610.03178

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Keywords

amplifier, amplitude noise, phase noise, X-band, HBT, cross-spectrum, power summing, frequency synthesis, voltage regulator

Citation

Hati, A. , Nelson, C. and Littrell, S. (2026), Residual AM and PM Noise of Selected X-Band Amplifiers, arXiv https://arxiv.org/pdf/2610.03178, [online], https://doi.org/10.48550/arXiv.2610.03178, https://nps-ext.nist.gov/nps/nps_public_api/api/Publication/file/962863 (Accessed October 26, 2026)

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