Phased array control using phase-locked-loop phase shifters

The authors investigate the use of phase-locked loops (PLLs) as phase shifters in the control of a phased antenna array. The phase error of a PLL can be altered by adding a DC offset voltage to the output of the phase detector. If a digital phase detector, with its inherently linear response, is used, then the phase error, and hence the relative phase shift, will vary linearly with applied control voltage. Such phase shifters can act on their own at VHF or they can provide an IF reference signal to a mixer to create a linear phase shifter at microwave frequencies. Four prototype phase shifters, fed in series, have been built, driving a linear array of four monopoles, in transmit mode at 1.5 GHz. By use of a single common control voltage, a single main beam can be swept through 180° with an accuracy of better than ±2° within the range ±70°