A helix or helical antenna is a type of antenna that utilizes a conducting wire wound in a spiraling helix shape mounted over a ground plane. A helix antenna is a type of directional antenna — the electromagnetic field typically rotates around the axis of the helix in either a clockwise or counterclockwise direction. Simple and practical, helix antennas were essentially designed to take the place of much larger antennas while maintaining the same wide bandwidth characteristics. A helix antenna is most often used with hand held satellite communication devices such as telephones, radios, and Global Positioning Systems.
A helix antenna is usually able to provide superior reception in instances where the receiving device has a poor view of the sky, such as under tree cover and in the midst of tall buildings. Its ability to lock-on to the greatest number of satellite signals at one time also provides more accurate reception when traveling in vehicles, and it will likely be pre-installed in future automobile models.
A helix antenna is capable of being operated in one of two main modes: broadside, or normal, mode and axial, or end-fire, mode. Broadside-mode helical antennas are generally used in situations where a smaller antenna is an important operational factor. These antennas were first used with Citizen’s Band radios in the US and Australia during the late 1960s, and are widely used today as typical FM receiving antennas in automobiles.
Axial-mode helical antennas are more suited for situations in which a fixed orientation of transmitter and receiver cannot be easily obtained. This type of helix antenna is most often used in satellite communication devices, such as telephones and Global Positioning Systems. When an axial-mode helical is used, both the transmitting and receiving antennas must have the identical handedness for optimum results.
In geometry, a helix is defined as a smooth three-dimensional curve with a tangent line that maintains the same constant angle with its fixed axis. A good example of a geometric helix is a coil spring. Helices may be right or left-handed. The handedness of a helix is determined by looking along the axis of the helix and turning it in a clockwise direction. If the helix appears to move toward the observer, it is a right-handed helix, but if it appears to move away, then it is a left-handed helix. A common hardware screw is an example of a right-handed helix.
