PURPOSE: To expand the straight line area in the phase curve by using piezoelectric ceramic elements being the combination of series and parallel resonators as one stage of ladder to a phase shifter and connecting a resistor in series with each resonator thereby mitigating the slope of a phase curve.
CONSTITUTION: The phase shifter 1 is provided with the series resonator 5 made of a piezoelectric ceramic, the parallel resonator 6 made of a piezoelectric ceramic similarly and resistors 7, 8 connected in series with the resonators 5, 6. The series resonator 5 and the parallel resonator 6 are combined as one stage of ladder and both the resonators 5, 6 are formed on a single board. The resistor 7 of both the resistors 7, 8 is connected to the input of the series resonator 5 and the other resistor 8 is connected to the ground side of the parallel resonator 6. Thus, the resonance resistors 7, 8 of the resonators 5, 6 are damped, resulting that the slope of the phase curve is mitigated, the linear range of phase is expanded and the detuning characteristic of the distortion factor for a demodulation signal is improved.