Spurious Emission

Spurious emissions are emissions on frequencies outside the necessary bandwidth whose level may be reduced without affecting the corresponding transmission of 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

Applicable limits and frequency range:

The limit, reference bandwidth, detector, and measurement range depend on the radio service, transmitter type, operating state, and applicable regional or product standard. The boundary between the out-of-band and spurious domains is therefore determined from the relevant rules rather than from a single universal frequency offset.

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

Regulatory Relevance

Spurious emissions are addressed by international recommendations such as ITU-R SM.329 and by the rules and standards applicable to the product and target market, including FCC, ISED, ETSI, and Japanese requirements. The product-specific document defines the actual limits and test method.

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

Need support with spurious emissions testing?
Explore our accredited RF and EMC test services for regulatory compliance across global standards: Testing Services Overview