Spurious Emission

Spurious emissions are unwanted radio frequency (RF) emissions that occur outside ±250 % of the necessary bandwidth of a transmitter and contain no useful information. According to ITU-R SM.329, they include harmonics, intermodulation products, parasitic signals, and frequency conversion artifacts. Spurious emissions form a subset of unwanted emissions, alongside out-of-band emissions.

Causes of Spurious Emissions

Typical sources include:

• Harmonics of the carrier frequency

• Intermodulation products from nonlinear mixing

• Oscillator leakage (e.g., from PLLs or local oscillators)

• Clock harmonics in digital transceivers

• Modulation artifacts caused by insufficient filtering or nonlinearity

Measurement and Limits

Measurement units:

• dBm – absolute conducted power

• dBc – power relative to the carrier

• µV/m – electric field strength in radiated EMC testing

Measurement setups:

• Conducted measurements via RF ports and matched loads

• Radiated measurements in semi-anechoic chambers using calibrated antennas

Examples of spurious emission limits:

• 3GPP TS 25.104: –36 dBm in the 9 kHz–150 kHz band

• ETSI EN 301 390: –30 dBm from 1 GHz to 12.75 GHz

• ITU (satellite services): –70 dBm above 21.2 GHz

• 5G NR FR2: Measurements may extend to 5× the carrier frequency in mmWave bands

Some standards require spurious emission testing both during active transmission and in idle mode.

Regulatory Relevance

Spurious emissions are a critical compliance requirement in wireless certification. They are regulated by:

• ETSI standards: EN 300 328, EN 301 489, EN 301 390

• FCC: Part 15.209, Part 22, Part 24

• ISED Canada: RSS-Gen, RSS-210

• Japan (MIC): Ordinance 88

• International: ITU-R SM.329, CEPT/ERC Recommendation 74-01

Non-compliance may lead to test failures, interference complaints, or market access restrictions.

Applications

Spurious emission testing is required for:

• Wireless modules (e.g., Wi-Fi, Bluetooth, UWB)

• Base stations and 5G radios

• Medical RF equipment

• Automotive radar and V2X systems

• Satellite and telemetry transmitters

• RF development and evaluation platforms

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