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Split-type multiband bandpass filters (BPFs) and bandstop filters (BSFs) with input-reflectionless capabilities are reported in this letter. In the multiband BPF case, they consist of a duplexing network with a split-type multiband BPF channel—main channel—and its complementary resistively terminated multiband BSF channel—auxiliary channel—that absorbs the input-signal energy that is not transmitted by the overall filter. The multiband BSF counterpart is obtained from the latter by interchanging the roles of the main and auxiliary channels. The operational foundations, theoretical design rules, and synthesis examples of the devised split-type input-reflectionless multiband filters under a coupling-matrix-based formulation are described. Furthermore, for practical validation purposes, two microstrip prototypes corresponding to 3.85-/4.55-GHz second-order dual-band BPF and BSF circuits are constructed and measured.