What is an STALO and what are the phase noise requirements for a coherent radar?
STALO Phase Noise
Phase noise budget: the total system phase noise includes contributions from the STALO, the transmitter chain (amplifier AM-PM conversion, power supply noise), the receiver LO chain, and the ADC clock. Each contribution must be budgeted so that the total integrated phase noise meets the requirement. The STALO is typically the dominant contributor at close-in offsets (< 10 kHz), while the transmitter and power supply noise dominate at very close offsets (< 1 kHz) and the ADC clock jitter dominates at far offsets (> 100 kHz).
| 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
Which oscillator technology?
Crystal oscillators: best close-in phase noise (-140 dBc/Hz at 100 Hz offset at 100 MHz), but limited in frequency (need multiplication to reach RF). Dielectric resonator oscillators (DRO): good phase noise at microwave frequencies (-100 to -120 dBc/Hz at 10 kHz offset at 10 GHz). Sapphire-loaded cavity oscillators (SLC): ultra-low phase noise (-140 dBc/Hz at 10 kHz at 10 GHz), expensive and bulky. PLL synthesizers: flexible frequency selection but phase noise limited by the VCO and reference.
How do I measure radar phase noise?
Two methods: measure the STALO output directly with a phase noise analyzer, or measure the radar's clutter cancellation performance on a known clutter scene. The second method captures the total system phase noise (all contributors) as experienced in operation.