To improve the low frequency radiation characteristics of the radiating-wave simulator based on transverse electromagnetic (TEM) horn, a novel movable simulator made up of exponential-type TEM horn, two vertical perfect electric conductor (PEC) plates at its aperture, two sloping PEC plates and parallel resistance is designed firstly. The effect of different exponential tapered rates, the height of the two vertical PEC plates, the width of the source port and the parallel resistance at the end of the two sloping PEC plates to the near-field radiation performance of the novel simulator is simulated and optimized by finite-difference time-domain (FDTD) method. The radiation characteristics of the optimized novel simulator and its arrays is also given. The calculation results show that, the full width at half maximum (FWHM) of the electric field at the testing point which is 3 m away from the optimized novel simulator’s aperture center reaches 18.95 ns, and the optimized novel simulator’s sizes are 6 m×6 m×6.24 m while those of the normal simulator must be 9 m×12 m×6.8 m to get the same low-frequency radiation performance as that of the optimized novel simulator. And higher peak-value of the electric field at the testing point of the optimized novel simulator can be got compared with the normal simulator. In addition, the ratio of the delayed oscillation’s amplitude of the electric field in time-domain at the testing point of the optimized novel simulator to its peak-value is significantly reduced compared with that of the previous studies, while the peak-value of the testing point of the optimized novel simulator keeps high. The electric field’s peak value at the center point in the testing plane of the optimized novel simulator’s 2×2 array model is the largest, and the effective region meeting the requirement of field 6dB uniformity on the testing plane of 2×2 array model has the largest domain; The effective region on the 2×2 array model’s testing plane has the largest horizontal range, followed by 2×1 array model; The effective regions on the testing planes of 2×2 array model and 1×2 array model have the largest vertical range.