Optimizing the substrate material and electrode structure of photoconductive antennas is crucial to improving their performance in radiating terahertz waves. Compared with traditional photoconductive antennas (PCA), interdigitated photoconductive antennas (IPCA) can build multiple array elements in a smaller photosensitive area and have superior radiation performance. In this paper, six types of IPCA with different number of array elements and electrode gaps were designed and developed. The reverse electric field between adjacent electrodes was eliminated by blocking metal layers. The radiation characteristics and polarization characteristics of IPCA were compared with traditional PCA (parallel electrode antenna and bowtie antenna). The changes of the radiation characteristics of IPCA with the number of array elements, electrode gap, pump light energy and bias electric field were further studied. Experimental results show that the THz pulse radiation amplitude of the 40-element IPCA is 30 times higher than that of a single antenna.