This paper presents a wideband substrate integrated H-plane horn antenna loaded with a novel E-plane corrugation. Classical SIW H-plane horn antennas suffer from poor impedance matching, large E-plane half-power beamwidth and strong back radiation due to the thinness of the substrates. A substrate integrated E-plane corrugation is introduced as an effective solution, implemented using the multi-layer printed circuit board (PCB) technique. The elaborated corrugated SIW horn is well matched with reflection coefficients less than <inline-formula><tex-math notation="LaTeX">-</tex-math></inline-formula>10 dB from 26 to 40 GHz. The back radiation suppression reflected by front-to-back ratios is improved to minimum 20 dB and up to 40 dB in the entire Ka-band. Furthermore, the corrugation reduces the half-power beamwidth of the E-plane radiation patterns successfully, e.g. from 180<inline-formula><tex-math notation="LaTeX">^{\circ }</tex-math></inline-formula> to 80<inline-formula><tex-math notation="LaTeX">^{\circ }</tex-math></inline-formula> at 30 GHz, whereas the H-plane patterns are maintained and unaffected. Consequently, the antenna gain is well enhanced. A prototype of the corrugated horn is fabricated and then measured. The measurement is in good agreement with the simulation. The proposed corrugated SIW horn antenna is compact in a planar structure so as to easy integration and array deployment. The wide bandwidth, narrow E-plane half-power beamwidth and low back radiation make it very promising for applications as millimeter-wave probes or handset antennas.