Implementation of 3-D Bandstop Frequency-Selective Structures With Ultralarge Angular Stability Utilizing Narrow L-Shaped Strip Lines

In this article, a novel implementation method for 3-D bandstop frequency-selective structures (FSSs) with ultralarge angular stability is presented, utilizing narrow L-shaped strip lines (NLSLs). The resonator comprises NLSLs printed on both sides of a printed circuit board, symmetrically rotating with respect to each other. The structures designed based on the NLSLs resonator offer significant advantages, including large angular stability of the ultrawide stopband for dual polarizations, as well as low-passband insertion loss (IL). To illustrate the working principle, a miniaturized design example and its corresponding equivalent circuit model were developed, with a size of $0.13\lambda _{0} \times 0.13\lambda _{0} \times 0.25\lambda _{0}$ . The angular stability of the described bandstop structure can reach up to 70° for dual polarizations. Two samples were fabricated and measured. The measurement results reveal that the miniaturized NLSLs-based structure can provide an ultrawide stopband, with its −10-dB fractional bandwidth (FBW) of up to 53%. Furthermore, an FSS sample encompassing an ultrawide stopband from 4 to 12 GHz was readily implemented using our method, exhibiting exceptional angular stability. In conclusion, our proposed method fills the gap of the existing dual-polarized bandstop FSSs to obtain a large −10-dB FBW of more than 26.2% and could be a good guidance for designing the future microwave FSS radome and shielding structures.