Pulse Compression
Understanding Pulse Compression
Pulse compression resolves the fundamental conflict in radar design: long pulses provide more energy (better detection range) but poor range resolution; short pulses provide fine resolution but limited energy. Pulse compression gets the best of both by using a long pulse with internal modulation.
Pulse Compression Methods
- Linear FM chirp: Most common. Frequency sweeps linearly over the pulse. Processing gain = TB.
- Phase coding (Barker, polyphase): Pulse divided into sub-pulses with specific phase pattern. Barker codes provide ideal sidelobe properties for short codes (up to 13).
- Non-linear FM: Frequency swept with a non-linear function. Provides sidelobe weighting without SNR loss.
(T = pulse duration, B = modulation bandwidth)
Processing gain: PG = T x B (linear) = 10log(TB) dB
Compressed pulse width: tau_c = 1/B
Range resolution: delta_R = c/(2B)
Example: T=100 us, B=10 MHz:
CR = 1000 (30 dB), delta_R = 15m
vs uncompressed 100 us pulse: delta_R = 15 km
Frequently Asked Questions
What is pulse compression?
Pulse compression uses a long modulated transmit pulse and matched filter processing to achieve the range resolution of a short pulse with the energy of a long one. The compression ratio = time x bandwidth product (TB).
What is the time-bandwidth product?
TB is the product of pulse duration and modulation bandwidth. It equals the pulse compression ratio: how much shorter the processed pulse becomes. TB = 1000 means 1000x compression. Higher TB is better but requires wider bandwidth.
What are range sidelobes?
Pulse compression creates sidelobes in the range profile (time sidelobes of the autocorrelation function). These can mask weak targets near strong ones. Weighting windows reduce sidelobes at the cost of slightly degraded resolution and processing gain.