Properties of a 2D Periodic Leaky Wave Antenna at Microwave and Optical Frequencies



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Highly focused and directional beams of electromagnetic radiation can be obtained using a two-dimensional periodic leaky wave antenna (2D periodic LWA) formed by a periodic arrangement of metal patches on a grounded dielectric layer, excited by a simple source such as a slot in the ground plane. The slot in the ground plane launches a radially-propagating (cylindrical) TM0 surface wave, guided by the grounded substrate. This surface wave becomes perturbed into a leaky wave due to the periodic patches, resulting in radiation from a higher-order space harmonic (Floquet wave) of the leaky wave, producing a beam that is asymmetric, being narrower in the E plane than in the H plane. Such structures are extremely simple in construction and can produce very narrow beams at broadside. The leaky wave propagates anisotropically, having a complex wavenumber that varies with the angle of propagation. One of the goals of this investigation is to characterize the wave propagation and radiation characteristics of this class of 2D periodic leaky-wave antennas, and to show how the beam properties can be optimized. The phenomenon of directive beaming at optical frequencies using a periodically corrugated plasmonic metal (e.g., silver) film can be explained and studied in terms of leaky plasmon waves. The structure usually consists of a periodic set of grooves surrounding a subwavelength aperture in a thin silver film. At optical frequencies the silver has a negative permittivity due to plasmonic behavior, allowing for the guidance of a plasmon wave (similar to the TM0 surface wave that propagates on a grounded substrate layer at microwave frequencies). The grooves perturb the cylindrically propagating plasmon wave that is launched by the subwavelength aperture. Therefore, the structure has a physical principle of operation similar to the periodic metal-patch LWA at microwave frequencies. The theory developed for the microwave LWA discussed above is applied to the plasmonic directive-beaming structure to illustrate its fundamental principle of operation, and to show how it can be optimized.



Antennas, 2D periodic leaky-wave antenna, Leaky plasmon polariton, Directive beaming, Enhanced transmission