Demo — DRFM Deception

Demo — DRFM Deception#

Noise jamming shouts at the radar; deception lies to it. A digital RF memory (DRFM) captures the threat’s own pulse and replays modified copies that look exactly like real skin returns — and the classic move, range-gate pull-off, walks the radar’s tracking gate right off the target. This demo animates that sequence step by step.

The idea#

The radar tracks inside a range gate about one pulse width deep — \(150\) m for L4’s \(1\ \mu\text{s}\) pulse. A DRFM false return, made brighter than the skin echo, captures that gate, then ramps its delay to drag it out in range (recall \(\Delta R = c\,\Delta t/2\)). When the false return blinks off, the gate holds the last range it was dragged to and the true target — left behind ten gate widths ago — has slipped free.

The scope’s axis is measured as offset from the true target, so zero is the skin return and the gate is drawn to scale. These are the lesson’s numbers: a \(30\) km target, a \(150\) m gate, and a \(1500\) m pull-off at a believable \(300\) m/s — the same figures as the companion script, the type-along, and HW2 Q10.

Interactive demo#

Open in full screen

Walkthrough#

  1. Press Play and watch the capture. The gate (blue) is already locked on the true target (navy) — RGPO steals an existing lock, it does not acquire one. The DRFM false return (red) grows on top of the skin return at zero added delay until the gate’s AGC follows the louder copy. The truth and the lie are co-located, so the radar never notices the handoff.

  2. Watch the lock break. The false return walks out and drags the gate with it while the true target stays put. The dashed red line at \(75\) m is half a gate width: the moment the gate passes it the skin return falls outside the gate and the Skin return card flips to OUTSIDE GATE. At the default \(300\) m/s that is a quarter of a second into the walk.

  3. Watch the walk finish, then blink. The pull-off runs out to \(1500\) m over \(5\) s — ten gate widths — and then the jammer switches off. Nothing is left in the gate, so it holds the last range it was dragged to while the tracker coasts in memory. The separation callout reads in metres and in gate widths.

  4. Change the walk-off rate. The slider runs \(100\)–\(1000\) m/s. A faster pull-off breaks lock sooner but is easier for a deception-aware radar to reject on kinematics alone; a slower one is stealthier but leaves the jammer transmitting longer. Reset and run it again.

Key observations#

  • Deception attacks the measurement, not the power budget. Unlike noise jamming, it does not have to overpower the echo — it only has to be believed.

  • DRFM works because it is coherent. Replaying the radar’s own waveform produces a false return that passes the matched filter as genuine.

  • Every move has a counter. Leading-edge tracking and other ECCM eventually reject the walked return — the cycle from L11 continues.

Source#

MATLAB bundle · L18_RangeGatePullOff.m↓

The companion script models the same pull-off numerically — a \(150\) m gate, a \(1000\) m/s walk and a blink at \(1.5\) s — and prints how far the gate was dragged and whether the true target escaped it.

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