Splitter feeding network for array radiations of spoof surface plasmon polaritons

Abstract

Surface plasmon polaritons (SPPs) are two-dimensional electromagnetic (EM) fields, which are highly localized, propagate along metal-dielectric interfaces, and decay exponentially into adjacent media. Owing to the advantages of confined EM fields in subwavelength scales, SPPs have a lot of potential applications in super-resolution imaging, miniaturized sensors, and biosensing. Recently, in the microwave regime, an ultrathin corrugated metallic strip fed bya coplanar waveguide (CPW) has been investigated, which converts the guided waves to spoof SPP sin broadband with high efficiency. Such a plasmonic waveguide provides the required localization of SPP fields, solving the problem that SPPs cannot be excited efficiently on flat metallic surfaces in the microwave and terahertz frequencies. Based on the ultrathin corrugated metallic structure, many new devices have been proposed, including SPP filters, SPP frequency-selective devices, switches, and active SPP amplifier. In this work,we propose a splitter feeding network for array radiations of spoof surface plasmon polaritons (SPPs), which are guided by ultra thin corrugated metallic strips. Based on the coupled mode theory, SPP fields along a single waveguide in a certain frequency range can be readily coupled into two adjacent branch waveguides with the same propagation constants. We propose to load U-shaped particles anti-symmetrically at the ends of such two branch waveguides, showing a high integration degree of the feeding network. By controlling linear phase modulations produced by the U-shaped particle chain, we demonstrate theoretically and experimentally that the SPP fields based on bound modes can be efficiently radiated to far fields in broadside direction. The proposed method shows that the symmetry of electromagnetic field modes can be exploited to the SPP transmission network, providing potential solutions to compact power dividers and combiners for microwave and optical devices and systems.