Multilayered Reflectionless Wideband Bandpass Filters With Shunt/In-Series Resistively Terminated Microstrip Lines

A class of symmetrical multilayered reflectionless wideband bandpass filters (BPFs) with shunt/in-series resistively terminated microstrip lines are presented. Based on a wideband microstrip-to-microstrip vertical transition and two shunt resistively terminated multisection microstrip lines, wideband BPFs that feature broadband reflectionless behavior are first discussed. Subsequently, by increasing the number of cascaded stages in the resistively terminated microstrip lines, the improvement of both the reflectionless behavior and the passband amplitude flatness for this kind of absorptive wideband BPFs is demonstrated. Next, to avoid the cross-coupling effect appearing between the open-circuit-ended microstrip resonators and the shunt resistively terminated multisection microstrip lines, reflectionless wideband BPF counterparts that exploit in-series resistively terminated multisection microstrip lines are introduced, so that the stopband power-matching performance is further enhanced. Furthermore, a high-order reflectionless wideband BPF made up of the back-to-back cascade of two replicas of the previous absorptive broadband BPF as the constituent block is presented to prove applicability to higher selectivity realizations. The theoretical foundations of these reflectionless wideband BPF architectures are detailed. Besides, for experimental-validation purposes, a total of five 2-GHz prototypes corresponding to the different conceived reflectionless wideband BPF schemes are fabricated and tested.