Harmonic feedback-loop oscillator for pulling effect reduction and improved phase noise

A diplexer-based harmonic feedback-loop oscillator concept is presented and demonstrated at 5.8GHz. Without additional complexity, the diplexer together with an RF amplifier creates isolation between nonlinear feedback-loop dynamics and second harmonic signal component that is directed to the output. As a result, the load pulling effect is reduced as well as the phase noise performance is improved with reference to its fundamental feedback-loop counterpart. Load-pull measured results (VSWR ≤ 9) are observed follows: 1) load dependent frequency drift is significantly reduced from -19⁰/₀₀~15⁰/₀₀ to -0.75⁰/₀₀~1.06⁰/₀₀; 2) phase noise at 1MHz offset is improved by 15dB; and 3) output power is slightly affected only.