What is a horn antenna? What are the main principles and uses?

Horn antenna is a surface antenna, a microwave antenna with a circular or rectangular cross-section in which the terminal of the waveguide gradually opens. It is the most widely used type of microwave antenna. Its radiation field is determined by the mouth size and propagation type of the speaker. Among them, the influence of the horn wall on radiation can be calculated using the principle of geometric diffraction. If the length of the horn remains unchanged, the size of the mouth surface and the quadratic phase difference will increase as the horn opening angle increases, but the gain will not change with the size of the mouth surface. If you need to expand the frequency band of the speaker, you need to reduce the reflection at the neck and mouth of the speaker; the reflection will decrease as the size of the mouth increases. The structure of the horn antenna is relatively simple, and the pattern is relatively simple and easy to control. It is generally used as a medium directional antenna. Parabolic reflector horn antennas with wide frequency range, low side lobes and high efficiency are often used in microwave relay communications.

The radiation field of the horn antenna can be calculated from the surface field using Huygens' principle. The mouth surface field is determined by the mouth surface size and propagation wave pattern of the horn. Geometric diffraction theory can be used to calculate the influence of the horn wall on radiation, so that the calculated pattern and the measured value can be in good agreement up to the far side lobe. Its radiation characteristics are determined by the size and field distribution of the mouth surface, while the impedance is determined by the reflection of the speaker's neck (the beginning discontinuity) and the mouth surface. When the length of the horn is constant, if the opening angle of the horn is gradually increased, the size of the mouth surface and the quadratic phase difference will also increase at the same time, but the gain does not increase simultaneously with the size of the mouth surface, and there is a gain with the maximum value. Mouth surface size, a speaker with this size is called the best speaker. Conical horns and pyramidal horns propagate spherical waves, while fan-shaped horns that open on one surface (E or H surface) propagate cylindrical waves. The surface field of the horn mouth is a field with a quadratic phase difference. The size of the quadratic phase difference is related to the length of the horn and the size of the mouth surface.

Horn antennas are commonly 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. Unit antennas for phased arrays; 3. Antennas In measurements, horn antennas are often used as a common standard for calibration and gain testing of other high-gain antennas.