How is RF power defined and measured?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

RF power is normally quoted as average power into a specified load, typically 50 Ω. For modulated signals, the peak envelope power (PEP) and the peak-to-average power ratio (PAPR) matter because amplifiers must handle the peaks without distortion; OFDM signals commonly have PAPR around 10 dB or more before clipping.^[1]

What are the different power definitions?

Average power: time-averaged over many modulation cycles.
Envelope power: average over one RF cycle at a given instant; its maximum is PEP.
Instantaneous peak: of the RF waveform itself; 3 dB above envelope power for a sinusoid.
Available power from a source: P_av = |V_s|²/(4·R_s) (rms), delivered only into a conjugate match.
Delivered power: P_del = P_inc(1 − |Γ|²).

^[2]

What is PAPR and why does it matter?

PAPR (or crest factor in dB) is peak envelope power divided by average power. A constant-envelope signal such as FM or GFSK has 0 dB PAPR; multicarrier OFDM approaches Gaussian statistics and is usually specified by a CCDF curve. A PA must be backed off from saturation by roughly the PAPR, which lowers efficiency; techniques such as crest-factor reduction, Doherty amplifiers and DPD address this.^[1]

How is RF power measured?

Thermal sensors (thermocouple, thermistor) respond to true average power regardless of waveform. Diode sensors are fast and sensitive; they follow square law below roughly −20 dBm, and peak-power sensors use wide video bandwidth to capture the envelope.^[3] See RF power measurement.

Frequently asked questions

Is dBm average or peak?

By convention dBm values are average power unless stated as peak or PEP.

What is the PAPR of a sine wave?

0 dB in envelope terms; the instantaneous peak is 3 dB above average.

Why use 50 ohms?

It is a historical compromise between minimum loss (about 77 Ω) and maximum power handling (about 30 Ω) in air coax.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“RF Power Amplifiers for Wireless Communications, 2nd ed.”. S. C. Cripps, Artech House. 2006.
“Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.
“Fundamentals of RF and Microwave Power Measurements (Application Note 1449 series)”. Keysight Technologies. application note.

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