Helical Antenna

A helical antenna is an antenna with a helical shape. It is composed of a metal helix with good conductivity, and is usually fed by a coaxial line. The core of the coaxial line is connected to one end of the helix, and the outer conductor of the coaxial line is connected to a grounded metal mesh (or plate). The radiation direction of a helical antenna is related to the circumference of the helix. When the circumference of the helix is ​​much smaller than a wavelength, the direction of the strongest radiation is perpendicular to the helix axis; when the circumference of the helix is ​​on the order of a wavelength, the strongest radiation appears in the direction of the helix axis.

A helical antenna is a type of antenna that can transmit and receive polarized electromagnetic signals that rotate in space. This type of antenna is often used in ground stations for satellite communications. An unbalanced feeder, such as a coaxial cable, is used to connect the antenna. The center of the cable is connected to the helical part of the antenna, and the outer sheath of the cable is connected to the reflector.
From the outside, the helical antenna looks like a helix installed on a flat reflective screen. The length of the helical part must be equal to or slightly greater than one wavelength. The reflector is circular or square, and the maximum inner diameter (diameter or edge) of the reflector must be at least three-quarters of the wavelength. The radius of the helical part is between one-eighth and one-quarter of the wavelength, and the tilt angle must be between one-quarter and one-half of the wavelength. The minimum size of the antenna depends on the frequency of the low-frequency signal used. If the helix or reflector is too small, the efficiency of the antenna will be seriously reduced. The energy of the electromagnetic wave is the highest at the axis of the helical antenna.
A helical antenna usually consists of multiple helical parts and a reflector. The entire set of antennas can be moved vertically or horizontally at the same time to track a satellite. If the satellite is not in orbit, the azimuth of the antenna can be adjusted by computer to track the satellite trajectory.