What is insertion loss?
A practical definition of insertion loss for RF system designers, with worked examples for cavity filters and combiners.
Definition
Insertion loss is the reduction in signal power that occurs when a passive component is inserted into a transmission line. It is measured in decibels (dB) and is positive — a 1.8 dB insertion loss means the output is 1.8 dB lower than the input.
Why it matters in cavity filtering
Every cavity in a duplexer or combiner contributes some insertion loss. A 6-cavity duplexer with 1.8 dB total IL is well-designed; one with 3.0 dB has either poor cavities or a sloppy tune. The tradeoff is steep — every additional cavity buys you isolation but costs you a fraction of a dB.
Worked example
A 350 W transmitter feeding a duplexer with 1.8 dB IL delivers approximately 232 W to the antenna. The remaining 118 W is dissipated as heat in the cavities — which is why our duplexers are sized for continuous-duty operation.