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What EIRP limits apply to unlicensed antennas?

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Regulators limit radiated power either as EIRP/ERP directly or as conducted power with an antenna-gain allowance. In the US, 2.4 GHz digital transmission systems may use 1 W conducted with a 6 dBi antenna, i.e., 36 dBm EIRP for general use;[1] in Europe, EN 300 328 limits 2.4 GHz wideband transmitters to 20 dBm (100 mW) EIRP.[2] EIRP(dBm) = Pconducted − Lcable + Gantenna(dBi).

How do you check compliance for a given antenna?

Example (US, 2.4 GHz, general-purpose): a 9 dBi antenna exceeds 6 dBi by 3 dB, so conducted power must drop from 30 dBm to 27 dBm, keeping EIRP at 36 dBm. In Europe the same radio must keep EIRP at or below 20 dBm, so with a 9 dBi antenna and 1 dB cable loss, conducted power must be no more than 12 dBm.[1][2]

What are typical limits in other bands?

BandExample limitSource
US 902–928 MHz (DTS/FHSS ≥50 ch)1 W conducted, 6 dBi before reduction47 CFR 15.247[1]
EU 868.0–868.6 MHz SRD25 mW ERP, 1% duty cycleEN 300 220 band plan[3]
US UWB 3.1–10.6 GHz−41.3 dBm/MHz average EIRPPart 15 Subpart F[4]
US 5 GHz U-NIISub-band-specific limits47 CFR 15.407[5]

Does EIRP include beamforming gain?

Yes; for MIMO and beamforming transmitters, rules and test guidance define a directional gain that combines antenna gain and array gain depending on whether signals are correlated, which can force power reduction.[1][6]

Frequently asked questions

Is 36 dBm EIRP legal at 2.4 GHz in the US?

For general-purpose DTS operation with up to 6 dBi gain at 1 W conducted, yes, subject to the full rule.

What is ERP vs EIRP?

ERP references a half-wave dipole; EIRP = ERP + 2.15 dB.

Do cable losses count?

Yes; they reduce EIRP and can be credited where rules use radiated power.

References

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

  1. “47 CFR 15.247 — Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz”. U.S. FCC, eCFR. current text.
  2. “ETSI EN 300 328: Wideband transmission systems operating in the 2.4 GHz band”. ETSI. current version.
  3. “ETSI EN 300 220: Short Range Devices operating in the frequency range 25 MHz to 1 000 MHz”. ETSI. current version.
  4. “47 CFR Part 15 Subpart F — Ultra-Wideband Operation”. U.S. FCC, eCFR. current text.
  5. “47 CFR 15.407 — General technical requirements (U-NII devices)”. U.S. FCC, eCFR. current text.
  6. “KDB 447498: RF Exposure Procedures and Equipment Authorization Policies for Mobile and Portable Devices”. U.S. FCC Office of Engineering and Technology. current revision.
Categories: Regulations and safety