Near-field characteristics of a wideband travelling-wave antenna based on a tapered Half-Mode Substrate-Integrated Waveguide

In this paper the near-field distribution of a travelling-wave antenna based on a Half-Mode Substrate-Integrated Waveguide (HMSIW) is investigated in order to verify the guided-wave characteristics and the radiation mechanism of this antenna type. Open-ended coaxial probes are utilized to capture the electromagnetic power density at different positions along the antenna aperture. The measurement and simulation results show a good correspondence which validates the measurement technique. The presented results show fundamental differences between the tapered HMSIW antenna and the traditional uniform leaky-wave antenna (LWA). Unlike the uniform LWA, the radiation of the tapered antenna mainly happens close to cut-off position, thus small radiating effective length and an omni-directional radiation pattern are obtained.