Angle-of-arrival measurement via spectral estimation of radar time-of-arrival periodicities

Claim 1

A method to perform angle-of-arrival measurements (AOA) of radar signals using a first antenna and a second antenna separated by a distance d, wherein Time-Of-Arrival (TOA) values of the radar signals at the first and second antennas have been time tagged using Electronic Warfare (EW) receiver means and a TOA clock having a resolution T; the TOA values for the signals from the first and second antennas being represented respectively as TOA.sub.1 (i)=δ(n.sub.i) TOA.sub.2 (i)=δ(n.sub.i -mT) where k represents the discrete frequency components, the n i are the individual Time-Of-Arrival (TOA) data values and N is the last TOA value collected, and m =(0,1,2,. . . ); wherein said method comprises: determining the Pulse Repetition Intervals using a Discrete Fourier Transform (DFT) X 1 (k) for signals from the first antenna and X 2 (k) for signals from the second antenna as ##EQU8## where k represents the discrete frequency components, the n i are the individual Time-Of-Arrival (TOA) data values and N is the last TOA value collected; selecting peak values of k corresponding to the peaks of the modulus of the DFTs representing Pulse Repetition Frequency (PRF) for signals from the first and the second antennas; taking the phase values φ 1 and φ 2 respectively from the DFTs for the signals from the two antennas as ##EQU9## determining the difference between the phase values φ 1 and φ 2 for a peak value of k as ##EQU10## estimating a value for TDOA as: ##EQU11## determining the angle-of-arrival AOA as ##EQU12##

Claim 2

A method to perform angle-of-arrival measurements (AOA) of radar signals using a first antenna and a second antenna separated by a distance d, wherein Time-Of-Arrival (TOA) values of the radar signals at the first and second antennas have been time tagged using Electronic Warfare (EW) receiver means and a TOA clock having a resolution T; the TOA values for the signals from the first and second antennas being represented respectively as TOA.sub.1 (i)=δ(n.sub.i) TOA.sub.2 (i)=δ(n.sub.i -mT) where k represents the discrete frequency components, the n i are the individual Time-Of-Arrival (TOA) data values and N is the last TOA value collected, and m =(0,1,2,. . . ); wherein said method comprises: determining the Pulse Repetition Intervals using a Discrete Fourier Transform (DFT) X 1 (k) for signals from the first antenna and X 2 (k) for signals from the second antenna as ##EQU8## where k represents the discrete frequency components, the n i are the individual Time-Of-Arrival (TOA) data values and N is the last TOA value collected; selecting peak values of k corresponding to the peaks of the modulus of the DFTs representing Pulse Repetition Frequency (PRF) for signals from the first and the second antennas; taking the phase values φ 1 and φ 2 respectively from the DFTs for the signals from the two antennas as ##EQU9## determining the difference between the phase values φ 1 and φ 2 for a peak value of k as ##EQU10## estimating a value for TDOA as: ##EQU11## determining the angle-of-arrival AOA as ##EQU12##