An aircraft single-antenna FM radio altimeter

This article describes a frequency modulated single-antenna radio altimeter. The entire structure includes a transmitter/receiver network with a single antenna for operation in both a continuous wave (CW) mode and an interrupted continuous wave (ICW) anode to provide a highly accurate altitude indication. An altimeter transmitter generates a constant FM period CW signal below a critical altitude and a variable FM period ICW signal above the critical altitude. The main advantages of this altimeter are lower cost and weight, good measurement accuracy, and high altitude range.