ALTAIR

The ALTAIR (ARPA Long-Range Tracking And Instrumentation Radar) is a high-sensitivity, wide-bandwidth, coherent instrumentation and tracking radar designed for precise measurements of small, long-range targets. Operating at dual frequencies—VHF (155–162 MHz) and UHF (422 MHz)—it supports various modes, including tracking and signature collection, and contributes to a network of deep-space tracking sensors. Originally built in 1969, its deep-space capability with intrapulse modulation waveforms was added to the UHF system in 1982. The radar utilizes a steerable 46-meter dish antenna with a focal point VHF feed and a multimode Cassegrain UHF feed, incorporating a 5.5-meter frequency-selective sub-reflector. In the VHF band, ALTAIR employs a monopulse feed, transmitting right-circular (RC) polarized energy and recording left-circular (LC) sum, RC sum, LC azimuth angle difference, and LC elevation angle difference channels to determine three-dimensional target position and velocity. Capable of independently tracking up to 32 targets simultaneously in both VHF and UHF, it uses real-time ionospheric correction for enhanced accuracy and possesses sufficient power aperture to track geosynchronous satellites at slant ranges of approximately 40,000 km.

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