A direction finder system is described in which the phase of a signal from a spiral phase antenna is measured with respect to the phase of the same signal from a constant phase reference antenna in order to determine bearing. Phase is measured with an electronically controlled ferrite phase shifter. System components which were developed are described. Radiation pattern measurements at 700 mc of the antennas separately and as a system are reported. This direction finder determines bearings unambiguously. Simulaneous omnidirectional and directive azimuth antenna patterns are possible. Study of a coaxial TE11 mode ferrite rotator for possible incorporation in a cavity-backed annular slot spiral phase antenna is reported. As an alternative of ferrite devices, ferroelectric phase shifters are suggested. Large predicted phase shifts were achieved. Ferroelectric phase shifters offer potential advantages over ferrite phase shifters in size, weight, speed, and power requirements. (Author).