Enhancements in RF feedback oscillators using a microstrip resonator with second harmonic rejection

• Published in: Microwave and optical technology letters 2018-06, Vol.60 (6), p.1368-1374
• Main Authors: Urbina‐Martínez, J. L., Loo‐Yau, J. R., Moreno, P., Reynoso‐Hernández, J. A., Figueroa‐Reséndiz, B. E.
• Format: Article
• Language: English
• Subjects: bandpass filter; Bandpass filters; Circuit design; Feedback; Feedback circuits; feedback RF oscillator; Gallium arsenide; Harmonic reduction; harmonic suppression; Noise levels; Noise reduction; Oscillators; parallel coupled microstrip filter; Radio frequency
• ISSN: 0895-2477; 1098-2760
• DOI: 10.1002/mop.31160

In this article, the effect of the second harmonic on the microwave performance of RF feedback oscillators is investigated. A microstrip bandpass filter, which combines the characteristics of a 1st order coupled line and a hairpin filter allowing to reject the second harmonic, is used as feedback circuit. It is demonstrated that by mitigating the effect of the second harmonic the phase noise as well as the drain efficiency of the feedback oscillator are improved without affecting the output power at the oscillation frequency. Two RF feedback oscillator circuits based on GaAs FET were designed at 2.45 GHz with and without reducing the output power at the second harmonic. Experimental and simulated data have a high correlation and the results show that when the output power of the second harmonic is reduced it is obtained an improvement in the drain efficiency, phase noise, and second harmonic reduction of 36.61%, 14.75 dB, and 15.51 dB, respectively.