A push-push VCO using a phase shifter with 90° branch line hybrid circuit

In this paper, a wideband push-push VCO using a phase shifter is presented. The phase shifter consists of a 90° branch line hybrid circuit and varactor diodes. The oscillator is a positive feedback type oscillator. In the oscillator, the oscillating frequency can be changed by using the phase shifter as the electrical length of the feedback loops determine the oscillating frequency. The circuit structure is very simple and compact due to the double-sided MIC structure. This type of push-push oscillator is suitable for a wideband VCO compared with a negative resistance type one. In the experiment, the developed push-push VCO in Ku-band achieves wide tuning frequency range of 1.2 GHz (relative bandwidth =7.5%).