High-Selectivity Narrow- and Wide-band Input-Reflectionless Bandpass Filters with Intercoupled Dual-Behavior Resonators

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Two novel classes of high-selectivity input-reflectionless bandpass filters (BPFs) with narrow- and wide-band characteristics and out-of-band transmission zeros (TZs) are presented. These input-reflectionless BPFs, which are based on a complementary-duplexer approach, respectively, exploit intercoupled short-/open-ended dual- behavior resonators (DBRs) and coupled line/T-stub two-path transversal filtering stages in their main BPF channel. Their absorptive auxiliary channel is made up of a resistively terminated dual-band bipath transversal filtering cell, whose dual passbands are allocated in the stopband regions of the main BPF channel. Thus, the RF-input-signal energy that is not transmitted by the main channel in its attenuated bands is dissipated by the loading resistor of the auxiliary one. Hence, input-reflectionless properties are attained in the whole BPF architecture. The theoretical design principles of the conceived narrow- and wideband input-reflectionless BPF approaches are described. Furthermore, their experimental usefulness is verified through the development and characterization of two microstrip sharp-rejection BPF prototypes centered at 2 GHz.