Direction finder

Claim 2

A direction finder for deriving an approximation of the azimuth of a target source of signals, comprising: array receiving means having a plurality of receiving elements arranged in a spaced relation to receive the signals from said target source, central receiving means for receiving the signals from the target source; phase shift means for receiving signals from said central receiving means and generating a corresponding first signal having the same phase as the received signal and a second signal shifted 90° in phase with respect to said first signal; array commutation means for successively scanning the signal of each of said receiving elements for a commutation time interval and generating a select output signal corresponding to the scanned signal; coordinate generation means for receiving said first and second signals and said select output signal for each receiving element of the array and generating corresponding first and second coordinate average signals, said coordinate average signals representing a running average of the baseband rectangular components of the phasors for the signals received by the receiving element over a plurality of scans of the array; computation means for comparing azimuth candidate coordinate signals corresponding to the rectangular components of the candidate azimuth phasors of candidate azimuth targets to said first and second coordinate average signals of each receiving element to identify a candidate target azimuth having coordinate signals approximating the coordinate average signals of the receiving elements and an azimuth approximating the azimuth of the target source.

Claim 3

The direction finder of claim 1 wherein the receiving elements of said array receiving means are antennas arranged in a circular array.

Claim 4

The direction finder of claim 2 wherein said central receiving means is an antenna disposed at the center of said circular array of antennas.

Claim 5

The direction finder of claim 1 wherein said phase shift means includes: an intermediate frequency translation means for translating the signal received by said central receiving means to a corresponding intermediate frequency signal; a first phase locked loop means for receiving said intermediate frequency signal and generating said first signal in a phase-locked relation to the intermediate frequency signal; and a second phase locked loop means for receiving said first phase locked signal and generating said corresponding second signal shifted 90° in phase with respect to said first signal.

Claim 6

The direction finder of claim 1 wherein said array commutation means includes means for generating said select output signal at an intermediate frequency with respect to the signal of the target source.

Claim 7

The direction finder of claim 1 wherein said coordinate generation means includes: first integration means for integrating the product of the select output signal of a receiving element and the associated first signal over said commutation time interval and generating a corresponding integrated first coordinate signal; first averaging means for receiving the first coordinate signals that are generated over a plurality of scans of the array and generating for each receiving element the corresponding first coordinate average signal; second integration means for integrating the product of the select output signal of a receiving element and the associated second signal over said commutation time interval and generating a corresponding second integrated coordinate signal; second averaging means for receiving the second coordinate signals that are generated over a plurality of scans of the array and generating for each receiving element the corresponding second coordinate average signal.

Claim 8

The direction finder of claim 1 wherein said computation means includes a microprocessor for computing S factors relating the first and second coordinate average signals of the receiving elements to coordinate signals defining the rectangular components of the candidate phasors of candidate targets, and selecting the maximum computed S factor S K' and an associated index integer K' to derive a candidate azimuth approximating the azimuth of the target source.

Claim 9

The direction finder of claim 7 wherein said microprocessor includes means for interpolating between S factors S K'+1 and S K'-1 most closely associated with S K' to derive an interpolation index factor K C that may be added to the index integer K' to calculate an interpolated maximum index factor K P and a corresponding candidate azimuth more closely approximating the azimuth of the target source.

Claim 10

The direction finder of claim 8 wherein said microprocessor includes means for defining a point S K'+n between S K' and one of said most closely associated S factors and deriving an additional interpolation index factor that may be added to the maximum index integer K P to calculate an additional interpolated maximum index factor K P' and a corresponding additional candidate azimuth that most closely approximates the azimuth of the target source.

Claim 11

The direction finder of claim 1 including means for converting the signals received by said central receiving means to corresponding audio signals.

Claim 12

A direction finding method for deriving an approximation of the azimuth of a target source of signals, comprising the steps of: receiving target signals from said target source at a plurality of spaced receiving positions in a signal receiving array; receiving target signals from said target source at a central receiving position with respect to said signal receiving array; generating a first phase-locked signal corresponding to the target signal received at said central receiving position; generating a second phase-locked signal shifted 90° in phase with respect to said first phase-locked signal; successively scanning each of said spaced receiving positions in said signal receiving array for a commutation time interval and generating a corresponding select output signal for each scanned receiving position in said array; generating over each scan of said array a first and a second coordinate signal for each position in said array, said first coordinate signal corresponding to the integrated product of said first phase-locked signal and the associated select output signal and said second coordinate signal corresponding to the integrated product of said second phase-locked signal and the associated select output signal, the products being integrated over said commutation time interval; computing for each receiving position of the array a first running average of the first coordinate signals generated for the array position over a plurality of complete scans of the array, and a second running average of the second coordinate signals that are generated for the array position over a plurality of complete scans of the array; comparing measured phasors corresponding to the running averages of each receiving position of the array to candidate phasors of particular candidate targets; selecting the candidate azimuth target having candidate phasors most closely approximating the measured phasors; and determining an azimuth corresponding to the selected candidate target that approximates the azimuth of the target source.

Claim 13

A direction finding method for deriving an approximation of the azimuth of a target source of signals, comprising the steps of: receiving target signals from said target source at a plurality of spaced receiving positions in a signal receiving array; receiving target signals from said target source at a central receiving position with respect to said signal receiving array; generating a first phase-locked signal corresponding to the target signal received at said central receiving position; generating a second phase-locked signal shifted 90° in phase with respect to said first phase-locked signal; successively scanning each of said spaced receiving positions in said signal receiving array for a commutation time interval and generating a corresponding select output signal for each scanned receiving position in said array; generating over each scan of said array a first and a second coordinate signal for each position in said array, said first coordinate signal corresponding to the integrated product of said first phase-locked signal and the associated select output signal and said second coordinate signal corresponding to the integrated product of said second phase-locked signal and the associated select output signal, the products being integrated over said commutation time interval; computing for each receiving position of the array a first running average of the first coordinate signals generated for the array position over a plurality of complete scans of the array, and a second running average of the second coordinate signals that are generated for the array position over a plurality of complete scans of the array; comparing measured phasors corresponding to the running averages of each receiving position of the array to candidate phasors of particular candidate targets; selecting the candidate azimuth target having candidate phasors most closely approximating the measured phasors; and determining an azimuth corresponding to the selected candidate target that approximates the azimuth of the target source.

Claim 14

The method of claim 11 including converting the signals received at said central receiving position to corresponding audio signals.

Claim 15

The method of claim 11 wherein said step for comparing measured phasors and running averages includes: computing for each candidate target an S factor that relates the first and second running averages of the signals of the array positions to the corresponding coordinate components of the candidate phasor of the candidate target; and defining for each candidate target an index integer K that indicates the position of the candidate target with respect to a north azimuth reference.

Claim 16

The method of claim 13 wherein said step for selecting the candidate target includes: selecting the S factor having the greatest magnitude S K' .

Claim 17

The method of claim 14 wherein said step for determining the azimuth includes using the index integer K' of the maximum S factor S K' and the number M of array receiving positions to calculate the approximate azimuth according to the relation: 2πK'/M.

Claim 18

The method of claim 14 wherein said step for determining the azimuth includes: selecting S factors S K'+1 and S K'-1 most closely associated with the maximum S factor S K' and the index factor K' of S K' ; deriving a maximum interpolated index factor K P corresponding to the maximum point on a parabolic curve through the points S K' , S K'-1 and S K'+1 according to the relation: ##EQU6## using the maximum interpolated index factor K P and the number M of array receiving positions to calculate the approximate azimuth according to the relation: 2πK P /M.

Claim 19

The method of claim 14 wherein said step for determining the azimuth includes: selecting S factors S K'+1 and S K'-1 most closely associated with the maximum S factor S K' and the index factor K' of S K' ; deriving a maximum interpolated index factor K P corresponding to the maximum point on a parabolic curve through the points S K' , S K'+1 and S K'-1 according to the relation: ##EQU7## selecting an additional S factor S K'+1/2 ; deriving an additional maximum interpolated index factor K p' corresponding to the maximum point on a second parabolic curve through the points S K' , S K'+1/2 and S K'+1 according to the relation: ##EQU8## using the additional maximum interpolated index factor K P' and the number M of array receiving positions to calculate the approximate azimuth according to the relation: 2πK P' /M.