Arbitrary-Order Balanced Filter with Reflectionless Characteristics for Both Common-and Differential-Mode Signals

A novel arbitrary-order absorptive balanced filter is presented in this letter. It consists of an N-th order coupled-line bandpass filter with absorption networks terminated at its input/output ports. The absorption network is constructed by N sections of coupled-lines and absorption resistors. With the proposed architecture, not only common-mode (CM) noise but also out-of-band differential-mode (DM) signal can be directed into the absorption network and dissipated on the resistors, realizing reflectionless characteristics for both common- and differential-mode signals. Moreover, the proposed absorption network can greatly extend the reflectionless bandwidth compared to previously reported work. For demonstration, first-order, second-order and third-order microstrip prototypes are fabricated and measured. The measured results show wide-band reflectionless performance for both CM noise and DM signal.