Demo — Agility and Side-lobes#
A spot jammer is only powerful if it can find the radar’s channel. Frequency agility forces the jammer into a losing choice: a strong spot that the radar simply hops around, or a barrage spread so thin it barely registers. This demo makes that trade quantitative.
The trade#
A jammer that covers \(W\) of \(N\) channels denies a fixed radar only if it happens to sit on the radar’s channel. Against an agile radar it lands a hit with probability \(W/N\). If it instead barrages all \(N\) channels, its power per channel drops by \(10\log_{10}N\) dB.
Interactive demo#
Walkthrough#
Fixed radar, narrow jammer. With the radar parked and the jammer off its channel, nothing is denied. Slide the jammer onto the radar’s channel and denial jumps to 100% — a fixed radar lives or dies on one frequency.
Switch to agile. Now the radar hops across all \(N\) channels. The denied fraction drops to \(W/N\) — the jammer only catches the pulses that happen to land under it.
Widen the jammer. Increase \(W\) and the agile denial rises, but the jammer is spending power to cover more spectrum.
Force the barrage. Read the barrage-dilution number: spreading across all \(N\) channels costs \(10\log_{10}N\) dB per channel — at 16 channels that is 12 dB the jammer simply gives away.
Key observations#
Agility converts a power contest into a coverage contest — and coverage is expensive for the jammer.
Spot vs barrage is a dilemma, not a choice. Concentrate and be dodged; spread and be diluted.
More channels, more leverage. The defender’s advantage grows as \(10\log_{10}N\).
Source#
MATLAB · code/L15_FrequencyAgility.m↓
The in-class script sweeps the number of channels and jammer width, compares fixed against agile denial, and computes the barrage dilution penalty.