Time Domain Filtered

This thesis presents a technique for the detection of spread spectrum signals, of arbitrary form, even when the signal power spectral density (PSD) is well below the surveillance receiver noise spectral density, using a pair of antennas with broadband (I GHz or more) receivers. Cross correlating the outputs of two receivers, spatially separated by a distance of the order of one metre or more, produces a cross correlation function (ccf) in which the noise components are spread uniformly over the whole width while the signal component, the narrow autocorrelation function (act) of the spread spectrum signal, is concentrated near to the centre. The acfis displaced from the centre of the ccfby a small time shift equal to the time difference of arrival of the signal at the two antennas. A simple time domain filter can select a narrow centre portion of the ccf, rejecting the remainder which contains only noise. Taking the Fourier transform of this windowed ccf produces the "time domain filtered cross spectral density" (TDFCSD), in which the signal to noise ratio is independent of receiver bandwidth. Spread spectrum signals can then be both detected and characterised in an extremely sensitive broadband system by threshold detection applied to the magnitude of this IDFCSD. High resolution direction fmding can then be achieved by estimating the time difference of arrival at the two antennas from the phase slope of the appropriate part of the TDFCSD. An analysis of the performance of this dual receiver system is presented. A computer simulation illustrates the signal processing involved and shows excellent agreement with the analysis. An analysis of the detection performance of this system acting in an electronic support measure (ESM) role and comparison with other