Meaning
Spurious spectral components arise when two or more distinct carrier frequencies pass through a non-linear transmission medium or active semiconductor circuit. An intermodulation product consists of newly generated frequency tones located at mathematical sums and differences of the original input signals and their integer multiples. Wireless systems monitor these distortion products because odd-order terms often fall directly inside adjacent operational channels, corrupting receiver sensitivity and violating spectrum mask boundaries.
The phenomenon ceases to generate new spectral content once signal propagation returns to purely linear transmission media.
Spectral Placement
Mathematical combinations of carrier frequencies dictate the exact distribution of non-linear distortion tones across the radio spectrum. Third-order products, such as two times the primary frequency minus the secondary frequency, present severe interference risks because their resulting positions fall extremely close to the fundamental operational band. Narrowband filtering networks rarely possess sufficient steepness to attenuate an in-band intermodulation product without introducing unacceptable insertion loss to the desired transmission.
Receiver low-noise amplifiers facing strong out-of-band blockers produce these internal mixing products, which desensitize the receiver by raising the internal noise floor. Calculating spectral tone distribution allows RF engineers to select carrier channel spacings that avoid self-inflicted receiver blind spots.
Harmonic Distortion
Active components operating near saturation generate distinct distortion mechanisms. While harmonic distortion produces integer multiples of a single fundamental frequency far away from the passband, each intermodulation product requires multiple concurrent carriers and generates tones directly beside the operating channels. Power amplifier linearization circuits deliberately inject opposing phase distortions to cancel out these mixing artifacts.
Effective suppression maintains signal fidelity across wideband multi-carrier transmissions.
Filtering Requirement
System architectures employ specialized duplexers and filtering topologies to suppress non-linear tone generation. Mitigating every high-power intermodulation product demands exceptional linearity in passive connectors and receiver front-end filters. Substandard junction plating creates passive mixing that degrades base station receiver sensitivity.
