The horn antenna is a surface antenna, which is a microwave antenna with a circular or rectangular cross-section whose waveguide terminal is gradually opened, and is the most widely used type of microwave antenna. Its radiation field is determined by the size and propagation type of the horn. The effect of the horn wall on the radiation can be calculated using the principle of geometric diffraction. If the length of the horn remains the same, the size of the mouth and the quadratic phase difference will increase with the increase of the horn opening angle, but the gain will not change with the size of the mouth. To expand the frequency band of the horn, it is necessary to reduce the reflection at the neck of the horn and the mouth; the reflection will decrease as the size of the mouth increases. The structure of the horn antenna is relatively simple, the pattern is relatively simple and easy to control, and it is generally used as a medium directional antenna. Parabolic horn antennas with wide frequency bandwidth, low sidelobes, and high efficiency are often used in microwave relay communications.
The basic form of the horn antenna is formed by gradually expanding the opening surfaces of the rectangular waveguide and the circular waveguide. The opening surface of the waveguide is gradually enlarged, which improves the matching between the waveguide and the free space so that the reflection coefficient in the waveguide is small, that is, most of the energy transmitted in the waveguide is radiated by the horn, and the reflected energy is very small. With a reasonable choice of horn size, good radiation characteristics can be achieved: fairly sharp main lobe, small side lobes, and high gain. Therefore, the horn antenna is widely used in military and civilian applications and is a common test antenna.
Due to the simple structure of the horn antenna and the easy control of the pattern, it is usually used as a medium directional antenna, such as a standard horn, and is most commonly used as a feed for a reflective surface. When it is used as a stand-alone antenna, a phase-correcting reflector or lens is generally added. Horn-parabolic reflector antenna has the characteristics of the wide frequency band, low sidelobe, and high efficiency, and is often used in microwave relay communication. However, due to its heavyweight and complex structure, the lens has rarely been used for phase correction of speakers.
Horn antennas are often used in the following areas:
1. Feeds for large radio telescopes, reflective antenna feeds for satellite ground stations, and reflective antenna feeds for microwave relay communications;
2. The unit antenna of the phased array;
3. In antenna measurement, the horn antenna is often used as a general standard for calibration and gain testing of other high-gain antennas.