Two Types and Principles of Radar Antennas

　　Radar (Radio Detection and Ranging) antennas play a crucial role in radar systems, which are used for a wide range of applications, including air traffic control, weather forecasting, and military surveillance. There are two main types of radar antennas: parabolic dish antennas and phased - array antennas, each with its own unique design and operating principles.

　　Parabolic dish antennas are one of the most commonly used types in radar systems. The principle behind their operation is based on the reflection and focusing of electromagnetic waves. A parabolic dish antenna consists of a concave parabolic - shaped reflector, usually made of metal, and a feed horn located at the focal point of the parabola. When the radar transmitter generates an electromagnetic wave, it is fed into the feed horn. The feed horn then radiates the wave towards the parabolic reflector. The parabolic shape of the reflector is designed in such a way that it reflects the incoming waves and focuses them into a narrow, highly directional beam. This focused beam is then transmitted into space. When the beam encounters an object, such as an aircraft or a weather target, a portion of the electromagnetic energy is reflected back towards the radar antenna. The reflected waves are again collected by the parabolic dish and directed towards the feed horn, which converts the received electromagnetic energy back into an electrical signal for further processing by the radar receiver. Parabolic dish antennas offer high gain and excellent directivity, allowing them to detect objects at long distances with high accuracy. However, they have a limited field of view, and mechanical movement, such as rotation, is often required to scan different areas.

　　Phased - array antennas, on the other hand, operate on a different principle. Instead of using a single reflector like the parabolic dish antenna, a phased - array antenna consists of an array of multiple antenna elements, typically arranged in a planar or linear configuration. The key principle of phased - array antennas is the control of the phase of the electromagnetic waves radiated by each antenna element. By precisely adjusting the phase of the signals fed to each element, the antenna can electronically steer the radiation pattern without the need for mechanical movement. For example, in a linear phased - array antenna, if the phase of the signals from adjacent elements is adjusted in a specific sequence, the resulting electromagnetic waves will interfere constructively in a particular direction, creating a focused beam. By changing the phase settings, the beam can be steered to different directions rapidly. Phased - array antennas offer several advantages over parabolic dish antennas, including faster scanning speeds, the ability to simultaneously track multiple targets, and greater flexibility in beam - shaping. They are widely used in modern radar systems, especially in military applications where rapid target detection and tracking are essential.