A POWER COMPENSATION SYSTEM FOR PHASED OPERATION OF THE JET A2 ANTENNA ARRAYS

A large power transfer can occur between the coupled elements of the four-strap JET A2 antennas during operation with the elements phased at other than 0 or π. This transfer reduces the effective input resistance Rc of the element most lagging in phase and can even drive it negative, making matching to the transmitter impedance difficult or impossible. Large inequalities in the input powers to the four straps are also required if nearly equal current amplitudes on the radiating sections are to be obtained. A system for power compensation has been devised to counter this effect, which circulates power in the direction opposite to that occurring at the antennas. It is designed to work with the present rf control system, which provides automatic matching and continuous control of phase and amplitude of the antenna element currents. Cascaded coupled transmission line models of the A2 antenna array and feed circuits have been developed, including the power compensation system. The design of this system is discussed, together with predicted performance based on modeling results.