What is Harmonic?
A harmonic is a signal at a frequency that is an exact integer multiple of a fundamental reference frequency. In RF and wireless communications, harmonics are generated by non-linear components — particularly power amplifiers, mixers, and oscillators — and represent unwanted spurious emissions that can interfere with other systems operating at those harmonic frequencies. Managing harmonic emissions is critical in 5G base station and device design to meet stringent regulatory and 3GPP spurious emission requirements.
How Does Harmonic Work?
When a signal at frequency f passes through a non-linear device, the output contains not only the fundamental frequency f but also harmonics at 2f, 3f, 4f, and so on. The amplitude of each harmonic generally decreases with order, but even low-level harmonics can cause problems if they fall within the receive band of another system. For example, a 5G NR transmitter operating at 3.5 GHz generates a second harmonic at 7 GHz and a third harmonic at 10.5 GHz. Harmonic filtering — using lowpass or bandpass filters at the transmitter output — is the primary mitigation technique. 3GPP specifications define maximum spurious emission levels that implicitly limit harmonic content.
Use Cases
RF transmitter spurious emission compliance testing, power amplifier design and filter specification, coexistence analysis between 5G and satellite/radar systems, base station and UE regulatory certification, and interference investigation and resolution.
3GPP / Standards Reference
3GPP TS 38.104 (NR BS spurious emissions requirements), 3GPP TS 38.101 (NR UE spurious emissions), ITU-R SM.329 (Spurious emissions)
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
