US Patent 7567148 Frequency shunt

A frequency separating unit includes an antenna unit, a first signal path, a second signal path, first band-pass filter in the first signal path, a second band-pass filter in the second signal path, and a matching circuit between the antenna unit and the second band-pass filter in the second signal path. The matching circuit includes a shunt arm to ground that includes a first impedance component, and a parallel circuit that includes an acoustic wave resonator and a second impedance component. The matching circuit is configured to operate as a phase shifter and to produce a substantially open circuit at an input of the second filter in a pass band of the first band-pass filter.