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 CM and DM 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.