Patent ID: 7126444

Claim:
A multi-layer band-pass filter comprising: an unbalanced input for receiving unbalanced signals; a first balanced output and a second balanced output for outputting balanced signals; a band-pass filter section provided between the unbalanced input and the first and second balanced outputs and incorporating a plurality of resonators each of which is made up of a TEM line; and a multi-layer substrate used for integrating the resonators, wherein the band-pass filter section incorporates, as the resonators, an input resonator to which the unbalanced input is connected, and a half-wave resonator for balanced output to which the first and second balanced outputs are connected, the half-wave resonator for balanced output being made up of a half-wave resonator having open-circuited ends, the multi-layer band-pass filter further comprising a capacitor made up of part of the multi-layer substrate and provided in at least one of a location between the unbalanced input and the input resonator and a location between each of the first and second balanced outputs and the half-wave resonator for balanced output, the capacitor including: a first conductor layer connected to one of the input resonator and the half-wave resonator for balanced output via a through hole; and a second conductor layer opposed to the first conductor layer and connected to one of the unbalanced input, the first balanced output and the second balanced output.