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Low-profile omni-directional coupler for transverse magnetic surface waves Disclosure Number: IPCOM000183633D
Publication Date: 2009-May-29

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The Prior Art Database


The invention is a low-profile surface-wave coupler (SWC) that launches transverse-magnetic (TM) mode electromagnetic surface waves (SW) into a surface-wave medium (SWM). An electromagnetic surface wave is any wave confined to propagate along the two-dimensional interface between two medium, e.g. the interface between dielectric and air is the simplest case. An ideal surface wave’s fields propagate along the surface with sinusoidal variation and decay exponentially away form the surface. The fields have the form eikx e-αz , (See fig. 1) where k is the propagation wavenumber in the propagation direction in the SWM, and α is the decay constant away from the SWM surface. SWs can be used to communicate with and/or power devices distributed on the SWM surface. A TM SW is a surface wave whose magnetic field is parallel to the SWM surface and perpendicular to the direction of propagation. An SWM is any medium that supports SW propagation. It can be composed of the interface between two dielectric materials, such as kapton and air, or it can be created out of complex engineered textures applied to a surface (an example is shown in Fig. 2). The SWC is a device designed to transmit and receive SWs to and from the SWM without coupling to background radiation propagating in free space. An ideal SWC, when transmitting, will couple all of its energy to the SW in the SWM without radiating any power away form the SWM. Likewise, an ideal SWC, when receiving, will receive power only form SWs in the SWM and will not couple to any external free-space radiation. In one embodiment of the SWC of this invention, see Fig. 3, a circular metallic patch is one side of a square dielectric substrate, and a metallic groundplane is on the other side of the substrate. The groundplane may or may not have a thin dielectric coating. Metal coated via holes are dispersed symmetrically on the substrate; they electrically connect the two sides of the substrate, and are sized to tune the SWC to a particular frequency. A coaxial feed has its outer conductor soldered to the circular patch, and its center conductor is soldered to the groundplane. Additional holes can be drilled throught the substrate to tune its frequency after fabrication. The SWC is placed with its groundplane on the SWM to couple to the SWs. This embodiment is relocatable. In another embodiment, (see Fig. 4) the coaxial feed is connect in reverse; it’s outer conductor is soldered to the groundplane and it’s inner conductor penetrates through the substrate and is soldered to the circular patch. This embodiment is attached to the SWM with its coaxial feed extending through a hole in the SWM to its other side. It is not as easily relocated, but it offers advantage in improved free-space rejection