Rapid azimuthal determination of radio signals

#This invention relates to a method and system for finding the bearing of a radio signal.

#A number of methods are known for finding the bearing of a radio signal. For example, one may use a directional antenna and rotate the antenna until a null is detected. This is, however, rather slow.

#The present invention enables a completely automatic method of obtaining accurate bearings of radio signals and may be useful for numerous applications, e.g. as a surveillance means, in air-sea search and rescue operations, in direction finding applications at monitoring stations, as a scientific tool for radio propagation studies and as a base communication antenna receiving system.

#FIG. 1 diagrammatically illustrates a system in accordance with the present invention,

#FIG. 2 illustrates measured radiation patterns for three Beverage antennas, and

#FIG. 3 shows the relative response of antennas +1 and -1 with respect to antenna 0, the relative responses being shown by plotting the ratios A.sub.+1 /A.sub.0 and A.sub.-1 /A.sub.0 versus azimuth in degrees.

#Referring to FIG. 1, there is shown a rosette array, generally indicated at 10, of 12 directional antennas that have overlapping field patterns. A diode switch 13 is used to obtain instantaneous sequential samples of the twelve antenna terminal voltages. The antenna with the largest terminal voltage defines the approximate bearing of the incoming radio signal. The more precise bearing is obtained by comparing the terminal voltages on the two adjacent antennas, in a manner to be described later on.

#The rosette array of antennas results in twelve fixed beams with widths of 40.degree., separated by 30 .degree. in azimuth. The area occupied by an actual antenna array could be reduced by 1/2 of that shown in FIG. 1, since two beams pointed in opposite direction can be obtained with each Beverage antenna by sampling the voltages at either end, as discussed above. Therefore, six of the antennas shown could be eliminated. Of course fewer or more antennas could be used if desired, the arrangement shown in FIG. 1 being exemplary.

#The diode switch 13 comprises a single pole 12 position switch and it is conveniently housed at the center of the array. The switch 13 is controlled remotely at the receiving station and is capable of being switched within a fraction of a millisecond. The switch 13 allows for rapid sequential measurement of the twelve antenna terminal voltages in a time short compared to the fading rate of HF signals, the system according to the invention being particularly useful in connection with HF signals, although not limited thereto. Therefore, the amplitude of HF radio signals can be assumed to be constant during these short measurement periods.