Implementation of ultra‐miniaturised frequency‐selective structures based on 2.5D convoluted segments

A novel methodology for synthesising ultra‐miniaturised frequency‐selective structures (FSSs) is proposed. The methodology is based on interconnecting the convoluted segments, which are arranged alternately on both sides of the substrate. Three advantages of ultra‐compact unit cell size, independent control of filtering performance for different polarisations, and promising extension of multiband response are achieved. To verify this concept, two different structures are designed and fabricated. The first one is a single‐band FSS operating at 2.5 GHz, with a unit cell size of only ( λ 0 /34) × ( λ 0 /34). The second one is an ultra‐miniaturised dual‐band FSS with a band ratio of only 1.18, and its centre frequencies are located at 2.2 and 2.6 GHz. Stable dual‐polarised responses under various angles up to 60° are obtained.