A High Conversion Gain and Low Phase Noise Self-Oscillating Mixer Based on Positive Feedback Technique

The paper proposes a novel self-oscillating mixer (SOM) that exploits the strong nonlinearity of the BFP740 transistor in a positive feedback oscillation circuit for frequency mixing. By utilizing a high Q factor and high-isolation diplexer based on folded stepped impedance resonators, as well as a wide stopband low-pass filter, precise frequency selection and effective signal filtering are achieved. A SOM prototype with an area of 0.79λ₀ × 0.79λ₀ is designed, fabricated, and measured. The measurement results demonstrate that the proposed SOM exhibits oscillation at 2.26 GHz with a conversion gain of +10.5 dB when applied to an RF input frequency of 2.46 GHz at −30 dBm power, along with 1 dB compression point at −19 dBm. Additionally, the phase noise of the intermediate frequency signal is better than −107.56 dBc/Hz at 100 kHz.