A novel band rejection filter using a ground-through-hole ring (GTH-R) structure is presented. The GTH-R structure is a ring resonator with a cylindrical via hole in a microstrip substrate ground plane. This uniplanar compact GTH-R structure realizes an electric resonator in the stopband. The band rejection filter consists of microstrip line and some GTH-R resonators located on the both side of the microstrip line. The resonant frequency is proportional to the through hole diameter when the ring diameter is constant.
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