Filter unit having two attenuation poles

摘要

A filter unit comprising a band-pass filter for passing signals of a specified frequency band, a SAW filter for passing signals of a band around a frequency fp2 positioned between a cutoff frequency fc of the band-pass filter and an attenuation pole frequency fp1 thereof, and an inversion circuit for inverting the phase of the signal passing through the SAW filter and superposing the phase-inverted signal on an output signal from the band-pass filter.