AN/APN-232 Combined Altitude Radar Altimeter (CARA)

The AN/APN-232 CARA (Combined Altitude Radar Altimeter) is the standard US Air Force Radar Altimeter, used in C-5, C-17, C-130, OC-135, C-141, F-111, F-15, F-16, MH-53, T-43 and UH-1N aircraft. NavCom Defense Electronics, Inc., established in 1932 as Hoffman Electronics, is a high quality design and manufacturer of navigation systems, altimetry systems and test equipment for the Department of Defense.

The Combined Altitude Radar Altimeter (CARA) is an all-solid-state 0 to 50,000 ft FM/CW radar altimeter system operating at a nominal frequency of 4.3 GHz. It consists of a receiver/transmitter, antennas and indicators and offers inherent low probability of intercept and anti-jam capability as well as conventional analogue and digital outputs for aircraft avionic systems.Low Probability of Intercept (LPI) performance is achieved by control of the power output so that the transmitted power is the least amount required for signal acquisition and tracking. The system mechanisation automatically adjusts the required transmitter power to maintain normal system operation over varying terrain, aircraft altitude and attitudes.

The FM/CW technology, operating over a 100 MHz bandwidth, provides inherent spread-spectrum capability which further reduces detectability. The AN/APN-232 is easily maintained and offers low life cycle cost. The equipment incorporates highly modular packaging. The assemblies, subassemblies and components are 100 per cent screened and tested to stringent military standards. Ease of maintenance is achieved by using proven microprocessor-based digital display fault monitoring. These elements combine to produce a predicted system MTBF of greater than 2,000 hours. Low life cycle cost is obtained from high system MTBF, automatic self-test with fault isolation to both the line- and shop-replaceable units and a two echelon maintenance concept which maximises the use of shop-replaceable units that may be discarded rather than repaired.

The low probability of intercept altimeter's (LPIA) waveform permits high accuracy ranging and covertness, assuring mission success. The LPIA was developed and tested by the U.S. Navy for tri-service use. At its core is a high-speed digital signal processor and radio frequency module, operating on a frequency-hopped, spread-spectrum, phase-encoded, low-power signal waveform. This highly effective waveform and signal processing allows the LPIA to extend altimeter accuracy, performance envelope (roll, pitch, and altitude), jamming resistance, and low probability of intercept capabilities far beyond existing altimeters. High gain achieved in the receiver signal processing yields to low power output, resulting in a simple radio frequency design and eliminating multiple power amplifier circuits. These unique features help drive the in-field reliability to greater than 6800 hours. The LPIA modular design has complete backward compatibility with existing installations of the APN-194, APN-232, APN-209, and APN-171, eliminating A-kit costs by using interchangeable front panels.