Novel Sub-Harmonic Injection-Locked Balanced Oscillator

A novel sub-harmonic injection-locked balanced oscillator is proposed. The circuit provides two outputs with a 180° phase difference by employing a transmission line section for impedance transformation to meet the oscillation conditions. A coupling network is connected at the mid-point of the transmission line to inject the sub-harmonic frequency. This eliminates the need for a circulator or balun. The circuit is small and consumes low DC power. Under the locking state, the circuit provides double the injection frequency and also the phase noise of the two outputs is substantially improved.