Abstract: A bandpass filter in which a plurality of dielectric resonators are arranged in an array is disclosed. Two metallic posts each having a length which is substantially equal to a quarter of the wavelength of the fundamental frequency (center frequency of the bandpass filter) are arranged one between the dielectric resonator located at one end of the array and an input connector and the other between the dielectric resonator located at the other end of the array and an output connector. This suppresses propagation of spurious modes, particularly propagation at a twice higher frequency than the fundamental frequency.

Abstract: The interior of a metal housing is divided by a dielectric substrate into two compartments. At least one of the compartments is kept air-tight. The substrate carries thereon a semiconductor active element chip for oscillation within the air-tight compartment and a dielectric resonator within the other compartment. The chip and the resonator, electromagnetically coupled with the chip, constitute a microwave oscillator whose oscillation frequency can be stabilized. A metal screw is threaded into that wall of the housing which defines the other compartment in a predetermined positional relationship to the resonator. The metal screw is rotatable to vary the distance between the screw and the resonator and, thereby, the oscillation frequency.

Abstract: A transistorized microwave oscillator comprising a resonator 2 coupled to a transistor 4, 5 and a feedback capacitor 7' around the transistor which produces a fundamental oscillation frequency and harmonics thereof. The feedback capacitor is located within a cut-off waveguide 21 and couples oscillations into the waveguide which blocks the lower undesired frequencies.

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.