Radiated Spurious Emissions Mitigation in Multi Radio System Design
Radiated spurious emissions in multi-radio designs demand aggressive board-level isolation and predictive intermodulation filtering to secure market approvals.
Non Linear Junction
Meaning
Electrical interfaces with asymmetrical current-voltage characteristics alter the frequency content of signals passing through them. An active or unintended non linear junction behaves like a mixing diode when exposed to high-frequency radio transmissions, producing harmonic distortion and unwanted mixing products. This behaviour is typical of semiconductor components, but it also arises at corroded metallic joints.
The effect is localized to the contact interface and diminishes as the signal power decreases below the activation threshold, meaning that clean assembly prevents it.
Harmonic Generation
When radio frequency currents flow across a metal-to-oxide interface, the non-linear resistance generates new frequencies. These products include second-harmonic and third-harmonic frequencies that can interfere with the primary receiving antenna. In communication systems, this is a major cause of passive intermodulation, which raises the system noise floor.
Circuit Detection
Locating these problematic points requires specialized handheld test gear or laboratory receivers that measure returned harmonic energy. The test equipment transmits two high-power carrier tones and listens for the specific intermodulation frequencies generated by the suspected junction. Spikes in the returned signal indicate the presence of corrosion or loose connectors.
Prevention Method
Ensuring clean, tightly torqued mechanical connections remains the primary way to prevent these non-linear effects. Designers select metals with compatible galvanic potentials to prevent oxidation over the product lifespan. Gold or silver plating on RF connectors provides stable, oxide-free contacts that maintain linear impedance under harsh operating conditions.