a tacan beacon is disclosed in which the pulse - modulated carrier signal generated in a transmitter is applied to the elements of a circular antenna array through controllable phase shifters that generate 15 - hz and 135 - hz sidebands through , switches , and through a butler matrix . a switching facility generates two states . in the first state , the phase shifters are controlled to generate the upper and lower 15 - hz sidebands and the upper 135 - hz sideband , respectively . in the second state , they are controlled to form the respective opposite sidebands . the butler matrix generates , radio - frequency phase - rotation fields at the antenna . in the two states , the ordinal numbers of the radio - frequency phase - rotation fields differ in their signs . the absolute value of the largest ordinal number is smaller than or equal to six , and the sum of the absolute values of the ordinal numbers for the carrier signal and the upper or lower 135 - hz sideband is equal to 9 .