Lesson 18 Flashcards#
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1. How does deception jamming differ from noise jamming?
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.
2. What are a tracker's "bins," and how does each jamming type abuse them?
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.
3. What is DRFM and what does it do?
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.
4. Why is a DRFM false return so hard to tell from a real echo?
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.
5. How does a DRFM repeater differ from a plain transponder?
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.
6. What is false-target injection, and why does it work?
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.
7. Walk through the three steps of range-gate pull-off (RGPO).
(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.
8. How much range pull-off does an added DRFM delay buy?
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.
9. What is velocity-gate pull-off (VGPO)?
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.
10. How does inverse-gain angle deception fool a monopulse radar?
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.
11. Compare towed and expendable decoys, and why both beat chaff.
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.
12. Why does leading-edge tracking defeat RGPO?
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.
13. What is the realistic payoff of deception jamming?
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.