Apparatus for the detection of angles-of-arrival of radio frequency signals

Abstract

Incoming radio frequency signals from one or more remote transmitters, that may be changing or "hopping" in frequency, are received at two closely spaced antennas. A pair of Chirp-Z transform processors are respectively coupled to said antennas. The transform processors are operated in synchronism and produce a pair of sampled comb filter output responses, each of which comprises a multiple of frequency "bins" distributed over a given spectrum. The bins are read out of the Chirp-Z processors in a synchronous sequential order, and each bin is represented by a pair of signals in phase quadrature. The phase quadrature signals of corresponding bins are multiplied in a predetermined manner and the products thereof are selectively added and subtracted to provide a predetermined function (tan Φ) of the phase difference (Φ) between the signals incident on the pair of antennas. This predetermined function is coupled to a processor that calculates a trigonometric function (sin -1 ) thereof which is indicative of the angle-of-arrival of the incident wave(s).

What is claimed is: 
     
       1. Apparatus for detecting the angles-of-arrival of a wide spectrum of radio frequency signals comprising a pair of closely spaced antennas, a pair of Chirp-Z transform means each respectively coupled to one of said spaced antennas, said pair of transform means being operated in synchronism and providing a pair of sampled comb filter output responses each of which comprises a multiple of frequency bins distributed over said spectrum, the bins being outputted from said pair of transform means in synchronous sequential order, each frequency bin being represented by a pair of signals in phase quadrature, arithmetric means responsive to said phase quadrature signals to form a predetermind function (tanΦ) of the phase difference(Φ) between the respective signals received at said spaced antennas, and processor means coupled to the output of said arthmetric means for calculating from said predetermined function the angles-of-arrival of signals incident on said pair of antennas. 
     
     
       2. Apparatus as defined in claim 1 wherein the phase quadrature signals of synchronous bins contain the requisite phase difference information for angle-of-arrival determinations. 
     
     
       3. Apparatus as defined in claim 2 where in said arithmetric means serves to multiply the phase quadrature signals of corresponding sychronous bins in a predetermined manner, with the products thereof selectively added and subtracted to provide said predetermined function (tan Φ 
     
     
       4. Apparatus as defined in claim 3 wherein the phase quadrature signals R 1  and I 1 , R 2  and I 2  from said pair of transform means represent the real and imaginary parts of the received spectral lines or frequencies, and said predetermined function is given by: ##EQU14## 
     
     
       5. Apparatus as defined in claim 4 wherein the angle-of-arrival (φ) is determined as: ##EQU15## where A=2πf in  D, and where f in  is the input frequency, and D is the distance between the antennas in meters.