Maintaining the Directivity of Antenna Arrays

When a directive antenna array is used to maintain a certain minimum of signal in a given direction, or when a group of arrays are employed to provide intersecting space patterns, such as in the radio range beacon, it becomes necessary to maintain an accurate and constant relation between the phase and magnitude of the several antenna currents. Slight detuning effects in one antenna of a group will seriously alter the pattern. To overcome this trouble, a means of excitation has been developed which will hold a constant predetermined relationship between the various currents regardless of wide changes of antenna tuning. In brief, the system involves the use of constant current transmission lines built out with artificial sections to either (a) 90 degrees in length and connected in parallel, or (b) 180 degrees in length and connected in series. Experimental data show the system to function satisfactorily and to be decidedly noncritical in adjustment. The new airways radio range beacon stations are using the arrangement uith marked success and several broadcast stations have also applied its principles to their arrays.