Whitepaper

Amplifier Selection: What You Need to Know

Published by Ametek CTS

This technical note from AMETEK CTS, authored by product manager Nick Jones, serves as a practical guide to selecting the right RF and microwave amplifier for EMC, communications, aerospace, and defence applications. It begins by explaining amplifier bias classes: Class A amplifiers conduct over the full 360° cycle, offering the best linearity, lowest harmonics, and strong VSWR tolerance, but at the cost of lower efficiency and higher heat output. Class AB amplifiers are more efficient and compact but can suffer from crossover distortion and require software-controlled VSWR foldback protection in many cases. Class B is generally unsuitable for RF use. The document then covers key specifications engineers must understand, including gain, gain flatness, harmonics, saturated output power, P1dB linear power, and load VSWR, as well as pulse-specific parameters such as rise/fall time, duty cycle, pulse width jitter, and on/off ratio. A dedicated section on VSWR protection explains that impedance mismatches cause reflected power that can damage amplifiers, and cautions readers to look beyond manufacturer claims of "infinite VSWR" protection by asking whether gain foldback is required and at what threshold. The guide then compares amplifier technology types: solid-state amplifiers (using GaAs or GaN transistors) handle CW and pulsed signals across many form factors, while Travelling Wave Tube (TWT) amplifiers offer superior power at higher frequencies but require high-voltage supplies, warm-up time, and often harmonic filtering. Pulsed TWT variants can deliver kilowatt-range peak power but must not exceed their specified duty cycle, typically around 6%. The document closes by mapping these considerations to real-world applications, including radiated immunity testing, 5G wideband intermodulation testing (which demands