We present the design,fabrication,and characterization of two new types of terahertz photoconductive emitters.One has an asymmetric four-contact electrode structure and the other has an arc-shaped electrode structure,which are all modified from a traditional strip line antenna.Numerical simulations and real experiments confirm the good performance of the proposed antennas.An amplitude increase of about 40%is experimentally observed for the terahertz signals generated from the new structures.The special electrode structure and its induced local bias field enhancement are responsible for this radiation efficiency improvement.Our work demonstrates the feasibility of developing highly efficient terahertz photoconductive emitters by optimizing the electrode structure. We present the design, fabrication, and characterization of two new types of terahertz photoconductive emitters. One has an asymmetric four-contact electrode structure and the other has an arc-shaped electrode structure, which are all modified from a traditional strip line antenna. Numerical simulations and real experiments confirm the good performance of the proposed antennas. An amplitude increase of about 40% is experimentally observed for the terahertz signals generated from the new structures. The special electrode structure and its induced local bias field enhancement are responsible for this radiation efficiency improvement.Our work demonstrates the feasibility of developing highly efficient terahertz photoconductive emitters by optimizing the electrode structure.