Diana Eng KC2UHB visually shows how a Yagi Antenna works in a video at MAKE: Magazine
This is so easy to understand when you can visualize it this way!
Using a low power amateur radio transmitter and a simple light bulb receiver circuit, we see how radio waves and electromagnetic induction transmit energy and signals wirelessly through the air. We also see how dipole and Yagi antennas radiate their energy in different patterns. Read on to build your own dipole receiving antenna!