Wideband 3-D Bandpass Frequency Selective Surface With High Selectivity and Angular Stability

This letter introduces a novel wideband bandpass frequency selective surface (FSS) based on 3-D slotline structures, which exhibits excellent selectivity and angular stability. The proposed FSS comprises orthogonally arranged 3-D periodic printed circuit boards (PCBs) etched with slotline structures. By simultaneously loading an inductive strip and a series <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> structure based on interdigital capacitors at the center of the open-circuit slotline, a third-order filtering response with a controllable high-frequency transmission zero (TZ) is formed. In addition, a stepped-impedance short-circuited slotline is introduced to generate a controllable low-frequency TZ to further improve the passband selectivity. The working principle is elucidated through a detailed analysis employing equivalent circuit models (ECMs). Furthermore, to confirm the design concept, an FSS prototype is manufactured and measured.