Helixantennas

A helix antenna is a type of radio antenna that consists of a helix, or spiral, of one or more conductive elements. These antennas are commonly used for satellite communications, GPS, and in applications requiring circular polarization. The helical shape allows for a broad frequency range and a relatively simple construction. They can operate in two main modes: normal mode and axial mode.

In normal mode, the helix's axial length is electrically small compared to the wavelength. The antenna behaves like a short dipole or loop, and its radiation is generally omnidirectional. The circumference of the helix is the dominant factor in determining its radiation pattern and impedance. This mode is less common for high-performance applications.

The axial mode, on the other hand, occurs when the helix's circumference is around one wavelength and its pitch angle is optimized. In this mode, the antenna radiates a directional beam along the axis of the helix. The radiation is circularly polarized, which offers advantages in reducing signal fading caused by multipath interference and orientation mismatches. The direction of circular polarization depends on the direction of the helix winding (left-hand or right-hand). The gain and beamwidth of the antenna are determined by the number of turns and the diameter of the helix.