The microstrip ring resonator was first proposed by P. Troughton in 1969 for the measurements of the phase velocity and dispersive characteristics of a microstrip line. In the first 10 years most applications were concentrated on the measurements of characteristics of discontinuities of microstrip lines. Sophisticated field analyses were developed to give accurate modeling and prediction of a ring resonator. In the 1980s, applications using ring circuits as antennas, and frequency-selective surfaces emerged.
