Abstract: A loop simulator is provided for testing radar altimeter systems. Several accurately calibrated delay lines and attenuation elements can be switched into and out of the signal path. Using these elements, the loop simulator can be configured to provide several common tests for radar altimeters. Switching of the various elements is controlled by a microprocessor, which determines the appropriate configuration based upon a mode input, and automatically switches the correct elements into the signal path. The controller automatically compensates for attenuation of the various elements.