How do I design the receiver protection circuit for a high power pulsed radar?
Receiver Protection
Gas tube limiters (TR tubes) handle very high peak power (MW level) with microsecond recovery. PIN diode limiters handle moderate power (10-100W) with nanosecond recovery. A typical cascade: gas tube → PIN pre-limiter → PIN fine limiter → LNA. The gas tube fires on the transmit pulse, dropping the leakage to 10-100W. The PIN pre-limiter limits this to 1-10W. The PIN fine limiter clips to +10 to +15 dBm. The LNA sees only the limited power, well below its damage threshold.
| 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
Frequently Asked Questions
What is spike leakage?
Spike leakage is the brief pulse of high-power energy that passes through the limiter before it fully activates. For PIN diode limiters: spike leakage lasts 1-10 ns at the turn-on of the TX pulse. The spike energy must be below the LNA's damage threshold. Specialty low-spike limiters achieve < 100 mV spike (< 1 ergs energy) for protecting sensitive GaAs LNAs.
How does recovery time affect minimum range?
Minimum range = c × t_recovery / 2. For 1 μs recovery: R_min = 150 m. For 100 ns recovery: R_min = 15 m. Faster recovery requires low-charge-storage PIN diodes or Schottky limiters. For automotive radar (77 GHz): recovery time < 10 ns is needed for < 1.5 m minimum range.