In this paper, a new low profile Substrate Integrated Waveguide (SIW) probe-fed H-plane horn antenna with improved gain is proposed. It consists of two waveguides, including a rectangular and a tapered one, in which both the first and third modes of the structure are simultaneously excited leading to a uniform field distribution along the radiating aperture of the antenna and in turn, its directivity is improved. Moreover, using a coaxial probe to excite the antenna, spurious radiation due to the feeding network is suppressed. The antenna structure is numerically analyzed using a software package, and a prototype is made using a single thin substrate layer. A good agreement is obtained between simulated and measured results. The measured results show 10.48 dBi gain which is 4.9 dBi higher than the gain of a conventional SIW horn obtained at 27.8 GHz. The introduced antenna is compact and can be used as a single antenna or as an element of a large antenna array.

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