The radar tester based on the Controllable Radar Cross Section (CRCS) is a device developed to test elements of primary radars. Unlike the devices supplied with most modern radar systems, this device tests every part of the transfer chain of the radar, including the antenne. Built-in testers feed their signals into the receiver, thus the antenne is not tested.
To test the radars, test flights are flown. Disadvantages of this method are that it is expensive and it is heavily dependent on weather conditions. Using a radar tester would let operators to test radars in a cost-effective way, and also difficult flight patterns are possible to simulate, such as rapid changes of speed.
The radar tester is based on the CRCS. It receives radar signals and alters them in a way it would be altered upon reflection from a real aircraft. The signal's amplitude is decreased proportionally to the path loss it would suffer travelling through the set distance, and it is also delayed accordingly. The phase of the reflected signal is also changed. When a moving target is simulated, the phase changes in time. This effect results in change of the frequency. This is known as the Doppler-effect.
Every target causes a fluctuation in the signal. This fluctuation is dependent on the orientation and shape of the target and also on its material. This can only be described by a stochastic variable. The device is able to simulate the fluctuation.
This signal is then transmitted back to the radar. When the radar receives the signal, it will treat it in the same way it treats signals coming from actual targets, eg. picks up the plot and starts a track based on it. During the test, the radar operates in normal mode, no adjustment is needed. This simplifies the test and ensures that the production of the recognized air picture will not be interrupted.