Passive microwave direction finding with monobit fourier transformation receiver and matrix coupled antenna

Abstract

A passive instantaneous microwave signal frequency identifying and angle of arrival identifying system employing a beam steering multiple element antenna coupled through a Butler matrix to a plurality of simplified Fourier transformation radio receivers wherein unit value or near unit value magnitudes of the Kernel function  - j2     π     kn N in the receivers' Fourier transformations are used to elude transformation computation complexity and resulting radio receiver size and cost penalties. Limiting amplifiers, a video signal path and direction finding encoding logic are also employed. Airborne military application of the system in electronic warfare direction finding, radar frequency determination and other activities is included.

We claim:  
     
       1. The real time passive digital method of identifying both operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy with respect to a receiving location, said method comprising the steps of: 
       receiving, in multiple elements of a circular disposed omni directional microwave antenna located in said receiving location, multiple antenna element samples of energy radiated from said distant source of microwave radio frequency radiant energy;  
       coupling electrical signals, generated by said received radiated energy in each of said circular disposed omni directional microwave antenna elements, through a mode forming electrical matrix to phase segregated multiple output ports of said mode forming electrical matrix;  
       communicating each of said mode forming electrical matrix phase segregated multiple output port electrical signals to a separate real time monobit electronic warfare radio receiver of substantially unit value real time digital Fourier transformation Kernel function                 -   j2                   π                 kn     N                     
       realization and signal phase angle preserving characterization; 
       determining, from real time digital Fourier transformation of said communicated phase segregated multiple output port electrical signal in one of said monobit electronic warfare radio receivers, a predominant signal frequency component of said energy radiated from said distant source of microwave radio frequency radiant energy; and  
       ascertaining, from phase decoding of digital Fourier transformations of multiple of said communicated, phase segregated, multiple output port electrical signals in said electronic warfare radio receivers, an angle of arrival vector, with respect to said receiver location, from said energy radiated from said distant source of microwave radio frequency radiant energy.  
     
     
       2. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  wherein said receiving location is disposed on a moving aircraft and said distant source of microwave radio frequency radiant energy comprises one of an airborne and a ground disposed radar system. 
     
     
       3. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  further including the step of dispersing said circular disposed omni directional microwave antenna elements into a flower petal-like array of individually signal output port-coupled elements. 
     
     
       4. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  wherein said coupling step is comprised or transferring said electrical signals through a mode forming Butler Matrix. 
     
     
       5. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  wherein said step of communicating each of said mode forming electrical matrix phase segregated multiple output port electrical signals to a separate monobit electronic warfare radio receiver of near unit value real time digital Fourier transformation Kernel function                 -   j2                   π                 kn     N                     
       includes a Kernel function of exactly unit value. 
     
     
       6. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  wherein said step of communicating each of said mode forming electrical matrix phase segregated multiple output port electrical signals to a separate monobit electronic warfare radio receiver of near unit value real time digital Fourier transformation Kernel function                 -   j2                   π                 kn     N                     
       includes a Kernel function of magnitude equal to the square root of two. 
     
     
       7. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  wherein said determining step further includes real time digital Fourier transformation of each said communicated phase segregated multiple output port electrical signal in a separate one of said monobit electronic warfare radio receivers and multiple determinations of a predominant signal frequency component of said energy radiated from said distant source of microwave radio frequency radiant energy. 
     
     
       8. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  further including the step of communicating signals from an output path of said mode forming electrical matrix to a signal input path of an angle of arrival computation. 
     
     
       9. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  further including processing output signals of said mode forming electrical matrix in a saturating amplitude limiting circuit. 
     
     
       10. The real time passive digital method of identifying operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  wherein said step of ascertaining an angle of arrival vector from phase decoding of digital Fourier transformations of multiple of said communicated, phase segregated, multiple output port electrical signals includes decoding a plurality of said phase segregated, multiple output port electrical signals each of different phase resolution and signal ambiguity characteristics. 
     
     
       11. Distant microwave signal source real time digital frequency identification and relative angular position-determination airborne tactical aircraft apparatus comprising the combination of: 
       a circular disposed multiple element microwave antenna member mounted in a microwave energy signal reception location of a host tactical aircraft;  
       a plurality of transmission line members each connecting between a feed point- location in one element of said multiple element microwave antenna member and an antenna signal output port;  
       a signal phase responsive beamforming electrical network having a plurality of signal phase processing elements disposed in an interconnected repetitive electrical matrix, said electrical matrix including an input port connected with said antenna signal output port transmission lines and an output port having a lesser number of microwave energy signal phase related output paths;  
       a plurality of Fourier transformation real time digital microwave frequency radio receivers each of substantially unit value-realized                 -   j2                   π                 kn     N                     
       Kernel function character, and having input port connection with one of said signal phase responsive electrical network signal phase related output paths; 
       said Fourier transformation real time digital microwave frequency radio receivers each also having constant input and output signal phase relationships and having digital output signals representative of Fourier components comprising said distant source of microwave radio frequency radiant energy operating frequencies; and  
       signal phase responsive angle of arrival determination apparatus connected with each digital output signal of said Fourier transformation microwave frequency radio receiver and with an angle of arrival output signal port of said airborne apparatus.  
     
     
       12. The distant microwave signal source real time digital frequency identification and relative angular position-determination tactical aircraft apparatus of  claim 11  further including a plurality of signal amplitude limiter elements each connected intermediate one of said signal phase processing elements of said signal phase responsive electrical network and an input path of one of said Fourier transformation real-time digital microwave frequency radio receivers. 
     
     
       13. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne tactical aircraft apparatus of  claim 11  further including a signal amplifier having a signal input port connected with one of said microwave energy signal phase related output paths of said repetitive matrix and a signal output port connected with an input port of said signal phase responsive angle of arrival determination apparatus. 
     
     
       14. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne apparatus of  claim 11  wherein said signal phase responsive electrical network comprises a Butler Matrix. 
     
     
       15. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne apparatus of  claim 14  wherein said Butler Matrix includes a plurality of microwave hybrid, microwave signal power divider and microwave signal phase shifter elements. 
     
     
       16. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne apparatus of  claim 14  wherein said Butler Matrix includes means for generating a plurality of phase related output signals each of differing and unit integer phase angle multiple relationships. 
     
     
       17. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne apparatus of  claim 14  further including a reference signal path connected between an output port of said Butler Matrix and a video reference signal input node of said signal phase responsive angle of arrival determination apparatus. 
     
     
       18. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne apparatus of  claim 11  wherein said transmission line members each comprise a length of coaxial cable. 
     
     
       19. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne apparatus of  claim 11  wherein said circular disposed multiple element microwave antenna member is comprised of circularly arrayed microwave frequency antenna elements located in a sunflower petal-like relationship on an electrical insulation substrate received in a surface portion of said tactical aircraft. 
     
     
       20. The distant microwave signal source real time digital frequency identification and relative angular position-determination airborne apparatus of  claim 11  wherein said Fourier transformation real time digital microwave frequency radio receivers each include digital Fourier transformation apparatus of two hundred fifty-six data points and substantially one hundred nanoseconds cycle time characteristics. 
     
     
       21. The real time passive digital method of identifying both operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 1  wherein said step of communicating each of said mode forming electrical matrix phase segregated multiple output port electrical signals to a separate real time monobit electronic warfare radio receiver of substantially unit value real time digital Fourier transformation Kernel function                 -   j2                   π                 kn     N                     
       realization includes a two hundred fifty-six data points digital Fourier transformation of substantially one hundred nanoseconds cycle time. 
     
     
       22. The real time passive digital method of identifying both operating frequency and relative angular location of a distant source of microwave radio frequency radiant energy of  claim 21  wherein said step of communicating each of said mode forming electrical matrix phase segregated multiple output port electrical signals to a separate real time monobit electronic warfare radio receiver of substantially unit value real time digital Fourier transformation kernel function                 -   j2                   π                 kn     N                     
       realization includes a two hundred fifty-six data points digital Fourier transformation of one hundred two and four-tenths nanoseconds cycle time.