Patent ID: 6914477

Claim:
A bandpass filter unit comprising: a first filter; a second filter having a frequency characteristic at feast in a frequency band for use that is substantially identical to a frequency characteristic of said first filter, said second filter being connected in parallel with said first filter; a first phase shift unit for shifting the phase by x degrees being cascade-connected to an input terminal of said first filter at a stage after parallel connecting points of the input terminal of said first filter and an input terminal of said second filter; a second phase shift unit for shifting the phase by y degrees being cascade-connected to an output terminal of said first filter at a stage before parallel connecting points of the output terminal of said first filter and an output terminal of said second filter; a third phase shift unit for shifting the phase by z degrees being cascade-connected to the input terminal of said second filter at a stage after the parallel connecting points of the input terminals of said first filter and said second filter; and a fourth phase shift unit for shifting the phase by w degrees being cascade-connected to the output terminal of said second filter at a stage before the parallel connecting points of the output terminals of said first filter and said second filter; wherein x, y, z, and w substantially satisfy conditions expressed by equations (1) through (3): (1)2 x −2 z =180 +n ×360 (n is a certain integer); (2)2 y −2 w =180 +m ×360 (m is a certain integer); and (3) x+y=z+w+l× 360 (l is a certain integer).