By flaring a dielectric waveguide in the H -plane, an H -plane dielectric horn is formed, which could be directly excited by an SIW feed. However, matching and radiation performances are poor due to the thinness of the substrate. To improve these performances, some periodic parallel strips are printed both on the top and bottom planes of the dielectric horn. These strips guide and leak the electromagnetic waves gradually along the horn, finally enhancing the end-fire radiation both in H -plane and E -plane. Moreover, they increase the impedance bandwidth up to 38% in Ka-band, and improve the realised gain by around 2 dB. Indeed, a gain of 14.3 dBi is achieved at the centre frequency, with a front-to-back ratio of 27 dB, a side-lobe level of -22 dB in the H -plane, and the narrowed E -plane and H -plane half-power beamwidth of about 20°. The measured and simulated results agree with each other very well. In addition, the proposed H -plane horn antenna is very compact, low cost, and could be easily integrated.