Abstract: A waveguide amplifier circuit has two semiconductor amplifier elements in a first waveguide circuit, a second waveguide circuit which is perpendicular to the first waveguide circuit and a termination circuit arranged at an end, remote from the semiconductor amplifier elements, of the second waveguide circuit. An abnormal oscillation component between the two semiconductor amplifier elements is attenuated by the second waveguide circuit and the termination circuit, thereby obtaining a high power output.

Abstract: In a frequency discriminator for a first and a second input signal of a first and a second frequency, a phase detector produces first and second rectangular pulse sequences. When the first input signal leads the second by 0.degree. through 180.degree., the first pulse sequence takes a predetermined peak value with an instantaneous frequency corresponding to the phase difference while the second one continuously has the peak value. When the first input signal lags behind the second by 0.degree. through 180.degree., the second pulse sequence takes the peak value with the instantaneous frequency while the first one continuously has the peak value. A low-pass filter rejects components of the first pulse sequence which are higher than the first and second frequencies.