Patent ID: 8005451

Claim:
A filter circuit, comprising: an input terminal configured to input signals; a first four-port element configured to receive input signals from the input terminal at a terminal A, divide the input signals received at the terminal A, and send each divided signals from a terminal B and a terminal C, and synthesize signals given to the terminal B and the terminal C and send synthesized signals from a terminal D; a first band stop filter configured to have a stop band including a center frequency of the input signals and configured to reflect signals falling in the stop band out of the divided signals sent from the terminal B to the terminal B and pass signals falling outside the stop band, wherein the reflected signals are given to the terminal B; a second band stop filter configured to have same stop band as the stop band of the first band stop filter and configured to reflect signals falling in the stop band out of the divided signals sent from the terminal C to the terminal C and pass signals falling outside the stop band, wherein the reflected signals are given to the terminal C; a first resonator group circuit configured to pass signals falling in a desired band out of the signals having passed through the first band stop filter by use of a first plurality of resonators; a second resonator group circuit configured to pass signals falling in the desired band out of the signals having passed through the second band stop filter by use of a second plurality of resonators each having same resonance frequency as that of each of the first plurality of resonators; a second four-port element configured to receive the synthesized signals from the terminal D of the first four-port element at a terminal E, divide received signals, and send each divided signal from a terminal F and a terminal G, and synthesize signals given to the terminal F and the terminal G and send synthesized signals from a terminal H; a third band stop filter configured to have same stop band as that of the first band stop filter and configured to pass the signals having passed through the first resonator group circuit to the terminal F and reflect the divided signals sent from the terminal F to the terminal F, wherein the signals having passed through the first resonator group circuit are given to the terminal F and the reflected signals are given to the terminal F; a fourth band stop filter configured to have same stop band as that of the first band stop filter and configured to pass the signals having passed through the second resonator group circuit to the terminal G and reflect the divided signals sent from the terminal G to the terminal G, wherein the signals having passed through the second resonator group circuit are given to the terminal G and the reflected signals to the terminal G are given to the terminal G; and an output terminal configured to output the synthesized signals sent from the terminal H.