Noise jamming attacks the power budget — it raises the threat's noise floor until the real echo drowns (it shouts). Deception attacks the measurement — it puts a plausible false return where the target is not, so the radar tracks a lie. Noise denies the picture; deception paints a fake one.
Bins are the cells a tracker keeps books in — a range cell, a Doppler cell, an angle cell. Noise masks a bin by burying it in energy; deception fills or shifts it with a false but believable return. Win the bin and you own what the radar thinks is true.
Digital RF Memory: a jammer that captures the threat's incoming pulse, digitizes and stores it, then retransmits modified copies under software control — setting precise delay, Doppler, and amplitude and replicating pulses to build false returns that look real.
It is a phase-coherent replica of the radar's own transmitted waveform, so it passes the radar's matched filter with full processing gain. The lie earns the radar's own gain — it comes through as cleanly and as loud as (or louder than) the real skin return.
A transponder replies after a fixed delay — one crude range-false target, and non-coherent, so it is easy to flag. A DRFM stores a phase-coherent copy and replays it with precise, programmable delay, Doppler, amplitude, and replication, making believable false returns.
Replaying the captured pulse at several delays/Doppler shifts to fill the range-Doppler map with believable replicas. A search radar drowns in plausible contacts (which is real?), and a tracker can be seduced into locking the wrong, brighter return.
(1) Cover pulse — a louder copy sits on the real return and captures the gate (the gate locks the jammer). (2) Ramp the delay — the false return walks out in range, dragging the gate with it off the target. (3) Blink off — the gate coasts on empty space while the true target, left behind, has escaped.
Apparent range shifts by \(\Delta R = c\,\Delta t / 2\) — the two-way factor, since the signal travels out and back. A \(1\ \mu\text{s}\) added delay walks the gate \(150\ \text{m}\) off the target.
RGPO's twin in the Doppler bin: start the false return at the target's true Doppler, then ramp a programmed frequency shift so the apparent velocity walks away, dragging the velocity gate off the target before blinking off. Run with RGPO, the false return pulls a range-Doppler diagonal.
A monopulse radar reads angle error from its \(\Delta/\Sigma\) (difference-over-sum) ratio. Inverse-gain jamming transmits a phase-inverted \(\Delta\) to null that ratio, so the radar reads zero angle error and the angle track freezes or drifts off.
A towed decoy is a repeater trailed behind the aircraft — brighter and offset, it seduces the lock away. Expendable decoys (MALD, ITALD) saturate the picture, bait radars into radiating, and transfer locks. Both beat chaff: no zero-Doppler notch problem, and they look like real moving targets.
The real skin return always arrives first; the cover pulse and walked-off false return arrive after it. A radar that gates on the leading edge of the return stays glued to the true target while the pull-off slides harmlessly behind it.
Time and doubt — it makes the radar work harder, look the wrong way, and coast on nothing for the seconds the platform needs. It rarely kills a track permanently, because ECCM (leading-edge tracking, digital monopulse, waveform agility, polarization, fingerprint discrimination) eventually counters it.