Echo Simulator Systems for Exomars 2016 Radar Doppler Altimeters tests

In the framework of Exomars Mission 2016, test equipment were developed in order to verify the performance of the Radar Doppler Altimeter onboard of the Entry, descent and landing Demonstrator Module before the Radar Field Test campaign. Three Echo Simulator Systems are currently involved into test activities of radar units. Their main task is the simulation of the echoes coming from Mars surface and their injection into the radars to test them in various operating conditions of descent trajectories and terrain behaviors. The Echo Simulator Systems are also used to collect the transmitted radar pulses and auxiliary signals to verify the correct radar transmission sequence in terms of pulse width, power and repetition interval. Echo Simulators Systems are able to simulate echoes in presence of wide terrain backscattering, altitude and attitude variations. The architecture is based on hi-speed Analog to Digital and Digital to Analog Converters commanded by a Field-Programmable Gate Array. A front end from Base-Band to Ka-Band has been designed to interface the equipment with radar and built to assure the required high dynamics and fidelity of signals. Two Echo Simulators are used in open-loops mode, injecting echoes generated by means of pre-processed trajectories to test the radars in standalone mode. The third one is by contrary used in closed-loop mode. It generates echoes using trajectories that are evaluated runtime according to radar units´ measurements feedback and simulated maneuvers of the descent module such as aero braking and thrusters´ activation. This mode permits to test the radars when integrated with the platform´s Guidance, Navigation and Control system.