MPAR (Multifunction Phased Array Radar) is the FAA and NOAA concept to replace ASR, TDWR, ARSR, and NEXRAD with a single S-band AESA phased array. A single MPAR installation would simultaneously provide terminal aircraft surveillance, en-route surveillance, and weather radar functions using time-multiplexed electronic beam steering, dramatically reducing the total number of radar sites and lifecycle costs.

Radar & Defense

Airport Surveillance Radar

Q: What is the weather channel on ASR?

ASR-9 and ASR-11 include a dedicated weather processing channel that extracts precipitation reflectivity data from the radar returns. The weather channel operates simultaneously with the aircraft surveillance channel, providing six levels of weather intensity displayed as color-coded regions on the controller's ARTS or STARS display. This enables TRACON controllers to vector aircraft around thunderstorm cells without requiring a separate weather radar.

Q: What is the difference between ASR-9 and ASR-11?

ASR-9 is a legacy analog system with a klystron transmitter producing approximately 1.3 MW peak power. ASR-11 (DASR - Digital Airport Surveillance Radar) replaces the klystron with a solid-state transmitter (25 kW average), uses digital signal processing, and integrates both PSR and SSR (Mode S) into a single digital architecture. ASR-11 provides improved MTI clutter rejection, better weather channel resolution, and significantly lower maintenance costs due to the elimination of the high-voltage klystron power supply.

/air-port sur-vay-lans ray-dar/ (ASR)

Airport Surveillance Radar (ASR) is the primary terminal-area radar system used by TRACON (Terminal Radar Approach Control) facilities to provide aircraft position and weather data within approximately 60 nmi of the airport. Operating at S-band (2.7-2.9 GHz), ASR systems rotate at 12.5 RPM (4.8-second update rate), using pulse-Doppler processing with MTI for ground clutter rejection and a dedicated weather channel for thunderstorm avoidance. The current FAA fleet includes the legacy ASR-9 (klystron transmitter) and the modern ASR-11 DASR (solid-state digital architecture), with the next-generation MPAR phased array concept planned to replace all terminal and weather radars.

Category: Radar & Defense

Band: S-Band (2.7-2.9 GHz)

Rotation: 12.5 RPM

Understanding Airport Surveillance Radar

ASR provides the "picture" that approach controllers use to sequence arriving and departing aircraft. The radar rotates continuously, painting each aircraft once per revolution (every 4.8 seconds). Each paint provides range (from pulse time-of-flight) and azimuth (from antenna pointing angle). The radar processor applies MTI to suppress ground clutter from terrain, buildings, and vehicles near the airport, while the weather channel extracts precipitation reflectivity for display as color-coded weather regions.

ASR systems co-mount a Secondary Surveillance Radar (SSR) antenna on the same pedestal. The SSR interrogates aircraft transponders at 1030 MHz, receiving coded replies at 1090 MHz that provide squawk code, pressure altitude (Mode C), and aircraft identification (Mode S). The PSR and SSR data are fused into a single track for each aircraft displayed on the controller's STARS terminal.

ASR Detection Performance

PSR detection range (S-Band):
R_max = [P_t·G²·λ²·σ / ((4π)³·S_min·L)]^1/4

ASR-11 parameters:
P_avg = 25 kW (solid-state), f = 2.8 GHz
G ≈ 34 dBi, Beamwidth ≈ 1.4° × 4°
R_max ≈ 60 nmi (10 m² RCS, P_d=0.9)

Update rate:
T_scan = 60/RPM = 60/12.5 = 4.8 seconds
Angular resolution: Δθ ≈ 1.4° at 60 nmi = ~1.5 nmi

ASR System Comparison

Parameter	ASR-9	ASR-11 (DASR)	MPAR (Future)
Transmitter	Klystron (1.3 MW peak)	Solid-state (25 kW avg)	GaN AESA
Signal processing	Analog + early digital	Full digital	Full digital + DBF
Weather channel	6-level reflectivity	6-level + Doppler	Dual-pol Doppler
SSR	Separate monopulse	Integrated Mode S	Integrated Mode S
Scan type	Mechanical 12.5 RPM	Mechanical 12.5 RPM	Electronic (no rotation)

Common Questions

Frequently Asked Questions

What is the weather channel on ASR?

ASR-9/11 include a dedicated weather processing channel that extracts precipitation reflectivity simultaneously with aircraft surveillance, providing six intensity levels displayed as color-coded regions on STARS. This allows controllers to vector aircraft around thunderstorm cells without a separate weather radar.

What is the difference between ASR-9 and ASR-11?

ASR-9 uses a klystron transmitter (1.3 MW peak). ASR-11 replaces it with solid-state (25 kW average), uses full digital signal processing, and integrates PSR and Mode S SSR into a single digital architecture. ASR-11 provides improved MTI, better weather resolution, and lower maintenance costs.

What is MPAR?

MPAR (Multifunction Phased Array Radar) is the FAA/NOAA concept to replace ASR, TDWR, ARSR, and NEXRAD with a single S-band AESA that simultaneously provides terminal surveillance, en-route surveillance, and weather functions via electronic beam steering.

Related Terms

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