In this paper a new Substrate Integrated Waveguide (SIW) H-plane horn antenna structure with enhanced directivity is proposed. The transition part of the proposed antenna consists of two parts with different length lead to increase the effective size of the aperture and so antenna directivity is improved. In order to suppress parasitic radiation and to reduce conductor loss, the modified horn antenna is fed by a coaxial probe. The proposed antenna is numerically investigated using HFSS software. Radiation properties of the proposed antenna including reflection coefficient, radiation patterns and directivity of the antenna are presented. Results illustrate that the modified H-plane horn antenna provide directivity of 8.36 dB which is 2.13 dB more than the directivity of a conventional H-plane horn antenna.

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