Substrate Integrated Surface-Wave Antenna

A surface-wave antenna integrated into a substrate is investigated. The substrate-integrated surface-wave structure can be considered approximately as a dielectric slab flush-mounted in a rectangular waveguide that has the top broad wall removed. The waveguide structure is investigated rigorously through the numerical solution of a magnetic-field integral equation. It is found that the dielectric-filled structure supports an improper waveguide mode and a proper surface-wave mode. The differences between the two modes are revealed, with the propagation and radiation characteristics and the equivalent magnetic current distributions in the aperture. The improper waveguide mode has such a high attenuation constant that it cannot provide a high directivity. On the other hand, the proper surface-wave mode that has a zero attenuation constant can be used to design a high-directivity antenna. A tapered-width substrate integrated surface-wave antenna is designed, fabricated and measured. With a planar structure, the antenna can be easily fabricated and can be flush-mounted on a conductor. Measured results show that the antenna has a wide gain bandwidth and a high gain with the main beam close to endfire.