With the increasing demand for multi-function and multi-band operation, more antennas have been employed in different electronic systems, which inevitably results in difficulties in antenna arrangement and severe interference. As a key technique of radio-frequency aperture integration, ultra-wideband (UWB) antennas provide an effective solution to this problem. A novel miniaturized UWB H-plane ridged horn antenna with end-fire radiation property is proposed in this paper. In order to broaden the operating bandwidth, an exponential ridge is employed and the cutting-off frequency of the rectangle waveguide is significantly reduced. By extending a hyperbola-shaped dielectric lens from the horn aperture, nearly uniform aperture phase distribution is achieved along the H-plane, which leads to a significant enhancement of the end-fire gain. This antenna has a compact form factor of only 0.57 λ_L×0.45 λ_L×0.11 λ_L and it maintains a wide operating bandwidth ranging from 0.8 GHz to 18 GHz. Moreover, the simulated cross polarization discrimination across the operating bandwidth is better than 30 dB. The antenna structure features a low profile, good stability, and easy fabrication, which can greatly facilitate its integration with metallic structures and missiles. Compared with other reported end-fire antennas, the proposed design shows remarkable superiority in terms of its electrical size and performance.