What are ACPR, ACLR and EVM?

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

Adjacent channel power ratio (ACPR, called ACLR in 3GPP) is the ratio of power in the assigned channel to power leaking into an adjacent channel, caused mainly by PA intermodulation (spectral regrowth). Error vector magnitude (EVM) is the rms difference between measured and ideal constellation points, normalized to the reference, expressed in percent or dB: EVM(dB) = 20·log10(EVM%/100).^[1]^[2]

How is ACLR measured?

A spectrum or signal analyzer integrates power over the main channel and adjacent channel bandwidths with specified filters and offsets. Analyzer noise and distortion must be well below the measured level; noise-correction and optimized attenuator settings help.^[3]

What degrades EVM?

PA compression and AM-PM.
LO phase noise (rotates constellation points).
I/Q gain and phase imbalance and LO leakage.
Thermal noise, filter group delay and quantization.

Contributions add approximately in rms: EVM_tot ≈ √(ΣEVM_i²).

What limits do standards set?

Standards specify ACLR and EVM per modulation; for example 3GPP NR base-station EVM requirements tighten for higher-order QAM (256QAM requires a few percent). Wi-Fi standards specify relative constellation error per MCS in dB. Consult the specification for exact values.^[1]^[4]

Frequently asked questions

Is ACPR the same as ACLR?

Essentially; ACLR is the 3GPP term and defines specific measurement filters.

What EVM does 1024-QAM need?

Very low, on the order of −35 dB or better, depending on the standard.

Does phase noise affect EVM?

Yes; integrated phase noise rotates symbols and adds to EVM.

References

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

“3GPP TS 38.104: NR; Base Station (BS) radio transmission and reception”. 3GPP. Release 17 and later.
“RF Power Amplifiers for Wireless Communications, 2nd ed.”. S. C. Cripps, Artech House. 2006.
“Spectrum Analysis Basics (Application Note 150)”. Keysight Technologies. application note.
“IEEE Std 802.11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”. IEEE. 2020 revision and amendments.

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