Combination of absorptive notch filter and tunable dual‐band conventional notch filter.

In this paper, a new kind of absorptive bandstop filter composing three series‐coupled lines is designed, investigated, and fabricated. The proposed circuit is indeed a combination of a dual‐band conventional notch filter and a single‐band absorptive filter generating two conventional and an absorptive notch. More precisely, the circuit introduces a fixed absorptive notch at 4.22 GHz and two electronically tunable (approximately 20%) conventional notches at 1.62–2 and 4.71–5.75 GHz, respectively. Besides, the FBWs of the first conventional notch, the second one, and the absorptive notch are 5.5 ± 1, 3.5 ± 1, and 3 ± 1%, respectively. The instantaneous surface current density of the circuit is depicted to investigate the generation of notches. The circuit has a compact size of 44.7 × 11.85 mm2 equaling to 0.489 × 0.129 λg2; moreover, it can successfully absorb more than 98% of the input power at its absorptive notch. [ABSTRACT FROM AUTHOR]