In this work, butterfly shaped photoconductive antennas (PCAs) on low-temperature grown (LT) GaAs and semi-insulating (SI) GaAs substrate as terahertz (THz) emitters are experimentally characterized and compared. Dependences of the THz radiated field on the applied DC bias voltage and laser pump power are compared. Quadratic DC bias dependence is seen for SI-GaAs PCA compared to a linear dependence for LT-GaAs PCA. Scaling rule can be applied to the laser power dependence to fit the measurement data and the saturation can be attributed to the screening effect. Studies of material property influence on THz radiated power allow exploration of ways to enhance PCA performance.