In this study, a novel TEM horn antenna design is introduced for Ground Penetrating Radar (GPR) applications. TEM horn antennas are mostly used in GPR for the advantages of high gain and power capability and wide bandwidth. At the low frequency of the GPR applications, the antenna size must be big. However with using shorting plate with conventional TEM Horn antennas, antenna size can be reduced. A novel shorting plate structure is presented. The effect of this structure and the contributions to antenna performance is investigated. HFSS simulations and measurement results of a prototype is presented. It has been seen that they are consistent with each other.