Folded microstrip resonator

A compact concertina shaped microstrip ring resonator, referred to here as a 'folded ring' resonator is shown to behave analogously to a microstrip annular-ring resonator. The folded ring resonator resonates at identical resonant mode frequencies as the annular-ring resonator, which is designed to operate at the same fundamental mode frequency and when fabricated on an identical dielectric substrate. It is also demonstrated that the folded ring when cut in half, referred to here as a 'folded half-ring' resonator, also exhibits similar transmission characteristics to a conventional annular-ring resonator. This resonator structure is even more compact. In addition, an input/output-coupling scheme to the resonator is employed that significantly improves the insertion loss and return loss performance of the resonant structures.