Comparative analysis of the electrical properties of a low noise oscillator embedded in a symmetrical square open‐loop with loaded stub resonator

The design of two types of miniaturized microstrip stub‐loaded square open‐loop resonators with asymmetrical feeder lines and their implementation into a microwave oscillator are presented in this article. The adopted resonator is based on a combination of electric and magnetic couplings in the central open gaps of the square loop resonators. The combined couplings generate an electromagnetic (EM) flux between the two square open‐loop resonators. The maximum coupling can be obtained by adjusting the open‐loop gap (the spacing between the two open‐loop resonators) and the orientation of the loaded‐stubs or T‐stubs inside the loop resonators. The asymmetrical port terminals also help couple EM energy by maintaining 50‐Ω impedance matching with the input/output devices. The improved high Q‐factor characteristics and the higher transmission zero result in high oscillator power and low phase noise characteristics. The square open‐loop with a loaded T‐stub resonator performance results are shown in a return loss of −24.8 dB, an insertion loss of −1.6 dB and a quality factor of 163 at 5.9 GHz C‐band application. In addition, careful design of the resonator resulted in an optimized oscillator. An oscillator with the proposed resonator shows good phase noise performance of −104.62 dBc/Hz at a 100 kHz offset from the carrier frequency of 6.2 GHz with an output power of 14.68 dBm. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2132–2136, 2014