Application of DSP in the Step-Frequency RCS Measurement System

Step-Frequency RCS measurement system is a new and remarkable RCS measurement system, which can obtain the response of target at each frequency point in an anecho chamber. Comparing it with traditional way of CW RCS measurement, more information gains in the new system. IFFT, zero insertion and the use of additional windows are some of familiar DSP techniques, which can improve the results if they are applied to the measurement. Using IFFT, the frequency domain data of whole chamber obtained by the measurement can be interpreted into time domain value, and the unwanted signals can be removed by adding a gate of range. Inserting zero in the frequency domain for increasing the points of IFFT will be good for finding response of target in the time domain exactly. The measurement of finite frequency spectrum makes the cut of data, the use of windows can reduce the effect of side lobe. Two metal spheres are measured in the anecho chamber. Two sorts of diameter are 50mm and 400mm respectively. The former is used for a target, the latter for scaling. The span of frequency is 8 GHz ∼ 12GHz, and the test frequency points are 801. Hamming windows are added to frequency domain data of the target and the scaler, then a number of zero as many as three times of frequency domain data are inserted for IFFT. A range gate is added to the target region where energy of target returns is much higher than the background. Returning to the frequency domain again, according to the results scaled, it shows that the accuracy of measurement is obviously improved. The value of RCS measurement is waved less than 1 dB around the center of frequency over 80%, in comparison with 4 dB waving over all test frequencies before, so it’s significant that integrating DSP techniques mentioned above is specially useful for RCS measurement of low scattering targets.