Single mode ring resonator with harmonic suppression

A single-side-access ring resonator for bandpass filter is presented. The characteristics of the resonator were investigated in terms of width and gap of the ring line and coupled-lines on microstrip. It is found that the frequency response and bandwidth of the resonator can be controlled by controlling the width and gap of the ring elements. The resonator was tested on Tachonic substrates and simulated using em fullwave simulator for verification. The response showed that at higher side of out-of-band frequency response, the resonator suffered with spurious effect. To improve the effect, a 3^rd order low pass filter was introduced which eventually modifies the ring structure. To validate the concept, the modified ring resonator was fabricated on Tachonic and the results showed improvement of spurious effect as compared to the nominal ring resonator. The rejection level of 30 dB was found at 4.34 GHz compared to the nominal design at 4.99 GHz with parasitic resonance at 2f_o had been successfully suppressed more than 20 dB. Based on this modified structure, the size had been reduced by 13.42 % compared to the nominal ring resonator.