An analysis of the performance of DRFMS for EW systems

The effects of systematic errors in a coherent I/Q circuit with digital detectors on frequency accuracy have been analysed and measured. An expression has been derived for the RMS accuracy of frequency measurement for ADCs with a given number of effective bits (N_ef ). No account has been taken of random noise on the signal and this may account for calibration not restoring maximum performance. The discrepancy is greatest at lowest and highest frequencies. At low frequencies, one channel provides consistently better N_ef than the other whereas the analysis assumes equal performance. Also, SNR _act has fallen from 34.5 dB at 10 MHz to 21.0 dB at 180 MHz and this may explain why calibration provides no benefit at high frequencies. It has been shown that a further improvement in accuracy may be obtained by a linear trade-off with bandwidth