One of the most common points of confusion in EMC test system specification is the distinction between continuous-wave (CW) and pulsed power amplifiers. They look similar in a catalogue and cover the same frequency ranges, but are designed for fundamentally different operating modes — using the wrong type compromises either test validity or the amplifier itself.

What CW and Pulsed Mean

CW amplifiers operate at full rated output indefinitely, with steady-state thermal dissipation and average power as the headline figure, since average = peak in CW.

Pulsed amplifiers produce very high peak power for short pulses followed by a longer rest period. A pulsed amplifier rated at 10,000W peak with 1% duty cycle only dissipates 100W average, but delivers 10,000W during the brief pulse.

Duty Cycle and Its Implications

Duty cycle = (Pulse Width / Period) × 100%. The WWPA and TWWPA pulsed series are rated at 1–4% duty cycle. Operating above this causes thermal overload. Never run a pulsed amplifier in CW mode, and never run a CW amplifier at pulsed peak power above its rated output.

Which Standards Require CW Amplifiers

IEC 61000-4-3 uses an 80% AM-modulated CW carrier throughout the sweep. IEC 61000-4-6 conducted immunity also uses AM-modulated CW at lower power. CISPR 25/36 automotive component testing uses CW and modulated CW. DO-160 Section 20 CW segment tests 100 MHz to 18 GHz continuously.

Which Standards Require Pulsed Amplifiers

MIL-STD-461 RS103 and GJB151C RS103 specify pulsed testing in some tailored test plans for radar-dense environments. DO-160 Section 20 includes a modulated pulse segment alongside CW. HIRF testing for large aircraft involves both CW and pulsed requirements, with pulsed peak fields of 1500–7200 V/m simulating surveillance and weather radar.

The Solid-State vs TWT Decision Within Pulsed

Solid-state pulsed amplifiers (WWPA series) cover 0.9–18 GHz with peak powers from 1000W to 20,000W across four frequency bands, all at 1–4% duty cycle.

TWT pulsed amplifiers (TWWPA series) use a travelling wave tube, producing higher peak powers with better linearity at extreme power levels, typically used when peak power requirements exceed solid-state capability at a given frequency.

Practical guidance: use WWPA solid-state where peak power requirements fit, for lower maintenance and immediate operation; use TWWPA where peak power exceeds solid-state capability or pulse fidelity requirements point to TWT; for HIRF requiring very high peak powers across multiple bands, multi-rack TWT systems combined with solid-state pre-amplification may be needed.

High-Power Pulsed Systems — WWPPA Series

For peak powers beyond the WWPA series, the WWPPA range provides extreme-power pulsed capability up to 15,000W across 1–18 GHz, used for the most demanding scenarios including full-aircraft HIRF simulation and high-power radar environment simulation.

Practical Checklist for Amplifier Type Selection

1. What is the test signal waveform in your standard? CW/modulated CW needs a CW amplifier; defined pulse width and repetition rate needs a pulsed amplifier.
2. If pulsed, calculate duty cycle and confirm it's within the amplifier's rated 1–4%.
3. Calculate required peak power using the field strength formula, adding 3–6 dB margin for cables, VSWR, and uniformity.
4. Can solid-state meet the peak power requirement at your frequency? If yes, prefer WWPA for maintenance and reliability; if no, use TWWPA.
5. Does your test plan combine CW and pulsed segments? If so, you need both amplifier types, switched by the test system.

A Note on Amplifier Protection

Both CW and pulsed amplifiers include protection circuits for voltage, current, temperature, and reflected power, but these aren't a substitute for correct operating practice. Always confirm antenna connection before enabling RF output, confirm duty cycle is within rated limits, allow correct warm-up time, and monitor reflected power — a high VSWR alarm means check the antenna, not increase drive.