Manipulating multipole resonances in spoof localized surface plasmons for wideband filtering.

The spoof localized surface plasmon (LSP) has been widely investigated but mostly with fixed multipole resonances. This Letter proposes a method to generate multipole resonances by adding a slit on the metallic ring of a complementary LSP. This slit theoretically introduces two new boundary conditions and new modes. To validate this approach, complementary LSPs with and without slits at three different angular positions are theoretically analyzed and numerically simulated. To validate and demonstrate the potential application of the proposed LSP structure, a bandpass filter (BPF) in a single-layer substrate is designed and measured by exciting the LSP with a slit on the metallic ring. The measured results show that by simply adding a slit, the BPF achieves a fractional bandwidth of 42.7% (2.5 GHz), for both |S11|<-10dB and |S21| within 1 dB variation. In the passband, a flat group delay between 0.57 ns and 0.75 ns is obtained. Moreover, the proposed structure features a low profile and a compact radius of 0.136 wavelength. By dynamically controlling slit/slits with varactors or diodes, the proposed structure is theoretically promising to be reconfigurable at microwave and even terahertz frequencies.

Shaping Bessel beams using source-integrated folded reflectarray.

This Letter proposes a highly integrated reflection-type approach to generate non-diffracting Bessel beams using a source-integrated folded reflectarray antenna (FRA). The FRA not only transforms spherical waves radiated by the feeding source to conical waves but also directly produces Bessel beams by specifying the phase distribution of reflectarray elements. To validate this approach, a millimeter-wave zero-order Bessel beam generator and a conventional collimated beam structure are analyzed, designed, fabricated, and measured. Good agreement among theoretical analysis, full-wave simulation, and experimental results demonstrate that the proposed FRA successfully generates non-diffracting Bessel beams and, moreover, the reflectarray elements are fully integrated with the feeding source in the same low-cost single-layered printed circuit board.