Interdigital Bandpass Filter Passband Shifting and Miniaturization Study Based on Via Hole Location and Diameter

This paper analyzes the passband shift of a microstrip line interdigital bandpass filter as a function of the position and diameter of the via holes. It was found that the passband shifted to a lower frequency range when the via hole was placed at the edge of the resonator and its diameter was reduced. To compensate for this passband shift, the length of the resonator was shortened and adjusted to match the intended 3400-3600 MHz bandwidth. The substrate used has a thickness of 0.762 mm, a dielectric constant of 2.97 and a loss tangent of 0.0012. As a result, based on the longest resonator used in this proposed structure, the size was reduced by approximately 13.15% compared to a conventional structure.