PURPOSE: To make the oscillating frequency highly stable against a temperature change, by picking up an output from a hybrid circuit, in an oscillator used for a millimeter wave band radio communication device.

CONSTITUTION: In Figure, the entire circuit consists of a band pass filter 1' comprising a dielectric resonator, an amplifier section combined with reflection type FET amplifiers 6, 7 and a 90° hybrid circuit 4, and a feedback type oscillator having a feedback loop with the hybrid circuit 5. They are made small in size and stable by adopting microwave integrated circuits. In this feedback type oscillator constitution, the entire circuit is separated into two parts; the amplifier section comprising the band pass filter 1' cosisting of the dielectric resonator, the reflection type FET amplifiers 6, 7 and the 90° hybrid circuit 4, and the feedback loop comprising the hybrid circuit 5. Since each of them is adjusted for the frequency characteristics against temperature change by the measurements, the characteristics of the two parts are so designed that they are cancelled with each other against the temperature change, allowing to realize the highly stable oscillator.