Antenna theory is the study of how antennas transmit and receive electromagnetic waves. Antennas convert electrical energy into radio waves and vice versa, allowing for communication over long distances. They come in various shapes and sizes, each designed for specific frequencies and applications, such as radio, television, and cellular networks. Understanding antenna theory involves concepts like radiation patterns, gain, and impedance. The radiation pattern shows how well an antenna sends or receives signals in different directions. Gain measures the antenna's ability to focus energy in a particular direction, while impedance ensures efficient power transfer between the antenna and its connected devices, like transmitters and receivers.