Airfield Surveillance Radar ASR 9

The Northrop Grumman ASR 9 (military designator AN/GPN-27) is an advanced Airfield Surveillance Radar (ASR) system, operational at 135 U.S. locations since its installation between 1989 and 1995. Operating at frequencies from 2.7 to 2.9 GHz, it was the first airport surveillance radar capable of simultaneously displaying weather and aircraft. The ASR 9 enhances aircraft detection in adverse weather conditions by combining circular polarization with moving target detection, featuring a separate weather channel that generates six weather levels, two of which can be selected by the controller. For detecting small targets amidst severe clutter, it utilizes a dual-beam antenna (transmitting on the low beam only), advanced digital processing, sophisticated constant false alarm rate (CFAR) circuitry, a scan-to-scan tracker, and a clutter processor with a fine-grain clutter map to improve returns from tangentially flying aircraft. The system is designed for unattended operation, incorporating a remote maintenance and monitoring system, with a dual-channel mean time between critical failures (MTBCF) exceeding 3,500 hours, supported by built-in test capabilities and redundancy in the antenna subsystem with dual drive motors and azimuth pulse generators.

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