How does pulse compression improve the range resolution and sensitivity of a radar?
Pulse Compression
The matched filter for a linear FM chirp is a filter with the time-reverse conjugate of the chirp. The output is a compressed pulse with peak amplitude T×B times the input amplitude, and width 1/B. Range sidelobes (the sidelobes of the compressed pulse) appear at -13.2 dB for an unweighted linear FM chirp. Sidelobe suppression using amplitude weighting (Hamming, Taylor) reduces sidelobes to -30 to -60 dB at the cost of 1-2 dB SNR loss and slightly wider main lobe.
| Parameter | Pulsed | CW/FMCW | Phased Array |
|---|---|---|---|
| Range Resolution | c/(2B) | c/(2B) | c/(2B) |
| Velocity Resolution | PRF dependent | Direct from Doppler | Coherent processing |
| Peak Power | High (kW-MW) | Low (mW-W) | Moderate per element |
| Complexity | Moderate | Low | High |
| Typical Application | Surveillance, weather | Altimeter, automotive | Tracking, multifunction |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
What limits the time-bandwidth product?
Practical TB products range from 10 to 10,000+. The upper limit is determined by: waveform generator bandwidth and stability, matched filter implementation complexity, and range sidelobe requirements (higher TB requires more precise weighting for low sidelobes). Modern digital waveform generators and FPGA-based matched filters support TB > 10,000.
Chirp vs phase coding?
Linear FM chirp: simpler hardware, Doppler-tolerant (still compresses well even with Doppler shift), but range-Doppler coupling (Doppler shift causes apparent range shift). Phase codes (Barker, Frank): Doppler-sensitive (compression degrades with Doppler shift), but no range-Doppler coupling. For most radar applications: linear FM chirp is preferred for its Doppler tolerance and simplicity.