Evolution of Antenna Technology: Apertures, waveguides, horns, and Vivaldi

Although the history of aperture antennas, such as those of waveguides and horns dates back to the early and middle 1930s, their remarkable advancement did not begin until the advent of microwave sources, such as the klystron and magnetron, in the late 1930s. These antennas, usually referred to as microwave antennas because of their operational frequency range, became very popular and played a key role in the development and advancement of radar systems, especially during WWII. Since then there have been a plethora of new designs and advancements, including the introduction of corrugations on their inner walls, to improve their radiation characteristics.