Effects of frequency and phase errors in electronic warfare TDOA direction-finding systems

Electronic warfare systems for use against military communication sources include direction-finding. The considered direction-finding electronic-warfare system uses two intercept receivers which are eavesdropping on the transmitted signal with no knowledge of the waveform used, or its origin. Down-conversion to baseband is required in order to digitize the received signal. This can be done using a superheterodyne receiver where an oscillator is used to mix the signal-of-interest to baseband. Errors in frequency and phase between the oscillators degrade the performance. Because of this error, the performance derived in previous work by the authors does not apply since the used model no longer is applicable. The extended model presented here considers the oscillator errors. The performance using the extended model is determined numerically and the result is compared to the Cramer-Rao lower bound for the ideal system using a typical signal waveform.