Abstract: A novel dipole array loaded substrate integrated H-plane sectoral horn antenna with a simple three-layered geometry is proposed. The dipole array integrated into two extra dielectric strips is connected to the top and bottom edges of the horn aperture. Both the horn aperture and the dipole array are effectively radiated together. A wide impedance bandwidth of 44% for vertical bar S-11 vertical bar < -10 dB that can cover the entire Ka-band is verified by a fabricated prototype. Additionally, stable symmetrical radiation pattern with low cross polarizations, low backward radiation, and gain up to 12 dBi with a variation of 3 dB can also be obtained throughout the whole operating band. The proposed antenna provides a new mean to design wideband substrate integrated horns with excellent endfire radiation, which would be attractive for future wideband and multiband millimeter-wave wireless applications, including the fifth generation (5G) mobile communications and the WiGig system.