ECM J/S ratio (SOJ)

Randle C. Sink

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For ECM, this app is to calculate the J/S ratio for the stand-off jammer (SOJ) situation. In this case, the jammer is at a different location than the target. While the target is in the main beam of the radar antenna, the jammer radiates power into the sidelobes. As an example, for a tracking radar, enter the power in kW antenna gain in dB, and IF bandwidth in MHz. Then enter the aircraft cross sectional area in m^2 and the range in km.

Next, for a jammer on board with transmitter power in kW over a bandwidth in MHz and given antenna gain in dB at a distance from the radar in km and a sidelobe in dB level for the radar antenna.

For example, Enter Pt = 100, Gr = 35, Br = 1, A = 4, R = 3, Pj = 1, Bj = 20, Gj = 10, Rj = 10, & SL = 20. Your value for J/S (SOJ) should be -14.0 dB.