This paper examines an efficient low phase noise oscillator using a high Q resonator and harmonic suppression filter. The oscillator is designed using a combined bandpass filter (BPF), which is used as a feedback element to an amplifier. The filter consists of an embedded spur line filter in the L-shaped input and output section which encloses a perturbed square ring. All of these sections are assembled to form a combined BPF which gives an excellent suppression of second and third harmonics. Low phase noise oscillator results are evaluated at 2 V power supply. The measured results show the fundamental frequency at 2.4 GHz, total output power of 14.92 dBm, phase noise -130.7 dBc/Hz at 1 MHz offset frequency, figure of merit (FOM) -175.64 dBc/Hz, reduction in 2nd and 3rd harmonics to below -45 dBm and DC-to-RF efficiency of 51.73%.
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