Radar test systems are essential in research, development, production and maintenance of radar systems. Most test systems measure single radar parameters or substitute components, but do not test the entire system including the antenna frontend. This application note presents a Rohde & Schwarz solution for testing the complete radar system which transmits any kind of radar signal by generating radar echo signals with arbitrary range, Doppler frequency and Radar Cross Section in response. Hence, arbitrary virtual targets are generated making it possible to perform real-time tests on many kinds of aerospace and defense or commercial radar systems.