A MULTIPLE UNIT STEERABLE ANTENNA 



357 



With nominally correct resistance termination standing waves of five 

 per cent usually occur. For standing waves not exceeding ten per cent 

 the accompanying phase distribution along the line does not depart 

 more than a few degrees from the desired linear distribution. The 

 use of the standing wave detector in routine operation was therefore 

 not required. 



Phase Shifters 

 Of the numerous methods of shifting phase the method ^'' illustrated 

 in Fig. 13 is the one chosen for the 18 circuits (3 branches, 6 antennas) 

 of the experimental MUSA. Here points a, b, d, and c have voltages 



^ ROTOR PLATES 



STATOR PLATES 



Fig. 13 — Circuit diagram and vector diagram of the phase shifter. The rotor plates 

 are especially designed to give a phase shift proportional to shaft angle. 



to ground 90 degrees apart. The potential of point b is IR; that of c 

 is — IR; that of a is jI/coC; that of d is — jI/coC. The resistance R 

 and reactance 1/coC are made equal at the mid-band frequency so that 

 four equal voltages, distributed equally over 360 degrees of phase, 

 appear on the four stators of the special condenser. A photograph of 

 this condenser appears in Fig. 14. Two specially shaped eccentric 

 rotors mounted in quadrature to each other on the same shaft com- 

 prise the output terminal. It will be noted that voltages of opposite 

 phase are connected to adjacent stators. Thus, with the rotors in 

 1' L. A. Meacham, U. S. Patent No. 2,004,613. 



