Band-pass filter

Claim 1

A band-pass filter comprising: a dielectric substrate; a grounded conductor layer formed on a back surface of the dielectric subsrtrate; an input transmission line conductor and an output transmission line conductor both formed on a front surface of the dielectric substrate; a plurality of resonators, each resonator having a fundamental resonance frequency f 0 , each resonator comprising a λ/2-length microstrip conductor (where λ is the line wavelength correspond to the fundamental resonance frequency, f 0 ) formed on the front surface of the dielectric substrate between the input and output transmission line conductors such that an adjacent pair of the plurality of microstrip conductors align in parallel over a predetermined length which is equal to or less than the λ/4 length; and a through hole formed through each of the plurality of microstrip conductors, the dielectric substrate and the grounded conductor layer at a center of the microstrip conductor, the through hole having a conductive layer formed on a wall of the dielectric substrate and electrically connecting the microstrip conductor and the grounded conductor layer; wherein the band-pass filter is rendered in a resonance condition only at the fundamental resonance frequency f 0 .