A novel left-handed structure is designed by periodically arranging metal wires and square diagonal-opening resonators on a single side of a substrate material. Based on the theoretical analysis and software simulation, the effective electromagnetic parameters of this designed left-handed material are extracted. The results show that, in the frequency band of 11.7-20.5 GHz, this structure possesses a good negative refraction effect and double negative characteristics and its absolute bandwidth is 8.8 GHz, which coverages the whole Ku band (8-12 GHz), and the loss of unit cell is less than 0.4 dB. Its real object is fabricated and tested, and its left-hand characteristic is confirmed. Compared with the conventional left-handed materials, the designed left-handed material realizes a low loss and a wide bandwidth.