Abstract: A portable test system is arranged to enable testing of an aircraft-mounted radar system. Simulated radar returns are transmitted via a test antenna positioned a short distance from an aircraft parked on an airport surface. The varying amplitude of received radar pulses is analyzed as the test antenna is illuminated by the main beam and side lobes of the radar antenna pattern as the radar beam is scanned. By controlling the amplitude of the simulated radar returns in inverse relation to the amplitude of received radar pulses, simulated radar returns inserted off beam center line are interpreted by the radar system as received on the beam center line. Test system transmissions, which may incorporate windshear effect test data, are thus enabled to create simulated effects usable for testing radar system response to a variety of airborne conditions, such as windshear. Test methods are also described.