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Power amplifiers (PAs) for RF/microwave use come in various shapes and sizes, at many different performance levels, and based on numerous technologies. Differences in capabilities separate one PA from another as a better fit for a particular system. But one key difference perhaps stands apart from the rest: Has the PA been designed for continuous-wave (CW) or pulsed amplification, such as in communications or radar systems, respectively. Furthermore, what characteristics can help make an amplifier a good fit for either a CW or pulsed application?
Whether based on vacuum tubes or solid-state semiconductor devices, PAs must be designed for either CW or pulsed operation--not for both modes. One reason is that the active devices within an amplifier are typically biased in such a way as to satisfy a blend of performance tradeoffs, including gain, linearity, efficiency, and output power for a target frequency or band of frequencies.
For example, if a CW amplifier with gallium-nitride (GaN) high-electron-mobility-transistor (HEMT) semiconductor devices is biased to generate 50 W output power with a 0-dBm input signal, it cannot simply be fed a short pulsed input signal at +3 dBm (or even a CW signal at that level) with the expectations of doubling the output power.
An amplifier that is not specifically designed for pulsed signals in general, or signals with a specific pulse width and pulse duration, can leave "traces" of itself on the output signal. These can be critical for defense-related applications, such as radar systems. For example, an amplifier that adds pulse traits such as ringing, overshoot, and droop to a boosted signal also makes a particular radar signal easily identifiable by an adversary due...