Achieving EMC in high frequency and high power switching environment on Radar Imaging Satellite

Satellite deck provides a challenging electro magnetic (EM) environment as the overall volume available is limited and a number of DC-DC converters and clocks are present. Add to this high frequency and high power switching the electro magnetic interference (EMI) scenario couldn´t be worse. Radar imaging satellite (RISAT) India´s first satellite with day night imaging capability, slated for launch by the third quarter of 2009 carries a synthetic aperture radar (SAR) as payload. SAR operating in c-band and radiating a whopping 2880 watts of peak power boasts of a 6mts times 2mts patch array antenna. The RF power is switched at 3.3 kHz rate. In transmit mode a clock of 5.35 GHz, occupies an ldquoONrdquo pulse duration of 20 mus. The ldquoOFFrdquo duration of about 0.3 ms is used to receive the reflected signal. This large power switching is an open invitation for EMI. Achieving electro magnetic compatibility (EMC) in such a scenario is a challenging task and needs innovative techniques. This paper describes the SAR payload, its operating principle, the various functional modes, and the challenges in achieving EMC onboard. The intricacies involved in drawing up a Test / qualification program for the pay load on ground is part and parcel of the paper. Even the test site selection and human safety issues occupy centre stage while handling such high powers.