Multi-Band Balanced Couplers With Broadband Common-Mode Suppression

Three novel single-/multi-band balanced couplers with wide-band common-mode suppression are proposed. In these double-functionality balanced-coupler architectures, double-sided parallel-strip line 180° phase inverters are used to realize the broadband common-mode rejection. Furthermore, by loading quarter-wavelength open/short-ended coupled lines at all ports of the single-band differential-mode coupler, dual/triple-band balanced operation with high isolation for the differential-mode power-division bands can be realized into it. For practical verification, three balanced couplers with single-, dual-, and triple-band operation at 1 GHz, 0.72/1.24 GHz, and 0.66/1/1.36 GHz, respectively, are constructed in microstrip technology and tested.