Analysis, modeling and simulation of ring resonators and their applications to filters and oscillators

Abstract

Microstrip ring circuits have been extensively studied in the past three decades. A magnetic-wall model has been commonly used to analyze these circuits. Unlike the conventional magnetic-wall model, a simple transmission-line model, unaffected by boundary conditions, is developed to calculate the frequency modes of ring resonators of any general shape such as annular, square, or meander ring resonators. The new model can be used to extract equivalent lumped element circuits and unloaded Qs for both closed- and open-loop ring resonators. Several new bandpass filter structures, such as enhanced coupling, slow-wave, asymmetric-fed with two transmission zeros, and orthogonal direct-fed, have been proposed. These new proposed filters provide advantages of compact size, low insertion loss, and high selectivity. Also, an analytical technique is used to analyze the performance of the filters. The measured results show good agreement with the simulated results. A compact elliptic-function lowpass filter using microstrip stepped impedance hairpin resonators has been developed. The prototype filters are synthesized from the equivalent circuit model using available element-value tables. The filters are evaluated by experiment and simulation with good agreement. This simple equivalent circuit model provides a useful method to design and understand this type of filters and other relative circuits.Finally, a tunable feedback ring resonator oscillator using a voltage controlled piezoelectric transducer is introduced. The new oscillator is constructed by a ring resonator using a pair of orthogonal feed lines as a feedback structure. The ring resonator with two orthogonal feed lines can suppress odd modes and operate at even modes. A voltage controlled piezoelectric transducer is used to vary the resonant frequency of the ring resonator. This tuned oscillator operating at high oscillation frequency can be used in many wireless and sensor systems.