How does pulse compression improve the sensitivity of a radar receiver?
Pulse Compression Processing Gain
Radar sensitivity is fundamentally limited by the energy in the transmitted pulse. A simple unmodulated pulse with duration T has energy proportional to T×P_peak. To achieve fine range resolution, T must be short, which limits the pulse energy unless peak power is very high. Pulse compression breaks this relationship by using a long coded or chirped pulse that fills the transmitter duty cycle while maintaining fine range resolution after matched filtering.
Linear FM (chirp) is the most common pulse compression waveform. The transmitted pulse sweeps across a bandwidth B during the pulse duration T. The matched filter in the receiver correlates the received echo with the transmitted waveform, producing an output pulse with width approximately 1/B (the compressed pulse) and amplitude proportional to √(B×T). The compression ratio CR = B×T directly gives the processing gain.
This processing gain appears in the radar range equation as a direct improvement in sensitivity. A radar with 30 dB pulse compression gain can detect targets 30 dB weaker (or 5.6× further) than the same radar without compression, or it can achieve the same detection range with 30 dB less peak power.
Processing Gain (dB) = 10·log₁₀(B × T)
Compressed pulse width ≈ 1/B
Example: B = 50 MHz, T = 20 μs
CR = 1000, Gain = 30 dB
Resolution = 1/50 MHz = 20 ns → 3 m
Frequently Asked Questions
What about range sidelobes?
The matched filter output has time sidelobes that can mask weak targets near strong ones. Sidelobe suppression techniques (amplitude weighting, nonlinear FM) reduce sidelobes by 30 to 50 dB at the cost of 1 to 2 dB processing gain loss and slight resolution broadening.
Can I use phase-coded pulses instead of chirp?
Yes. Barker codes, polyphase codes, and binary phase codes also provide pulse compression. Binary phase codes offer the advantage of constant modulus (no AM), but typically have higher range sidelobes than chirp waveforms.
Does pulse compression improve clutter performance?
Yes. The improved range resolution reduces the range cell size, reducing the clutter volume per cell. This improves the signal-to-clutter ratio, particularly for surface-based radars in ground clutter or sea clutter environments.