Log-Periodic Antennas vs Yagi Antennas

Both Log-Periodic Antennas and Yagi antennas are high gain directional antennas. The main difference between these antennas is that Log-Periodic Antennas support wider frequency bandwidths and are physically much larger than Yagi antennas. 

Conceptually, Log-Periodic Antennas are similar to Yagi Antennas. They can be thought of as two or three element Yagi antennas connected together, each tuned to a different frequency. This gives Log-periodic antennas the ability to work across a wide range of frequencies, whereas Yagi-Uda antennas are optimized for one particular frequency range.