A phase-locked-loop phase-shifter for band-limited signals

The need for a voltage-controllable phase-shifter frequently arises in radio astronomy interferometry work. This paper describes a particular implementation of such a phase shifter in which a phase-locked loop of special design is used as the principal phase-shifting element. Relative phase-shifting of a band-limited signal is accomplished by mixing the signal with a phase-shifted local oscillator output derived from the phase-locked loop. Details of circuit operation, construction and performance are presented. Particular attention is devoted to obtaining a wide range of phase shifts. The paper concludes with a description of three specific applications of the circuit to a radio source flux density measurement program.