This paper introduces a recently proposed end-fire leaky wave antenna (LWA) with high radiation gain and efficiency under vertical polarization. By periodically loading a series of shorting-pins in the double-sided-parallel-strip-line (DSPSL), a leakage region as well as end-fire radiation condition point can be generated on the fundamental mode of transmission line with normalized phase constant equal to 1. In order to enhance the radiation efficiency of the pin-loaded LWA, the U-shaped slots are etched at the vicinity of pins on the two surfaces of DSPSL to enlarge the attenuation constant values in the end-fire operation frequency range. Hence, the high end-fire gain with high efficiency can be realized on a compact structure with a limited antenna length. A prototype is designed in final, where the good agreement between simulated and measured results confirms the predicted performances of the proposed end-fire LWA.