Definition

helical antenna

Also see satellite.

A helical antenna is a specialized antenna that emits and responds to electromagnetic fields with rotating (circular)polarization. These antennas are commonly used at earth-based stations in satellite communications systems. This type of antenna is designed for use with an unbalanced feed line such as coaxial cable. The center conductor of the cable is connected to the helical element, and the shield of the cable is connected to the reflector.

To the casual observer, a helical antenna appears as one or more "springs" or helixes mounted against a flat reflecting screen. The length of the helical element is one wavelength or greater. The reflector is a circular or square metal mesh or sheet whose cross dimension (diameter or edge) measures at least 3/4 wavelength. The helical element has a radius of 1/8 to 1/4 wavelength, and a pitch of 1/4 to 1/2 wavelength. The minimum dimensions depend on the lowest frequency at which the antenna is to be used. If the helix or reflector is too small (the frequency is too low), the efficiency is severely degraded. Maximum radiation and response occur along the axis of the helix.

Helical antennas are commonly connected together in so-called bays of two,four, or occasionally more elements with a common reflector. The entire assembly can be rotated in the horizontal (azimuth) and vertical (elevation) planes, so the system can be aimed toward a particular satellite. If the satellite is not in a geostationary orbit, the azimuth and elevation rotators can be operated by a computerized robot that is programmed to follow the course of the satellite across the sky.

This was last updated in May 2007
Posted by: Margaret Rouse

Email Alerts

Register now to receive SearchMobileComputing.com-related news, tips and more, delivered to your inbox.
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

More News and Tutorials

  • Hospital chain boosts indoor cellular with distributed antenna system

    With terrible indoor cellular coverage impeding its ability to support mobile users, the hospital chain Baptist Healthcare System adopted a distributed antenna system from ADC. The system improved patient care at its hospitals and its ability to compete for physicians.

  • Cost-effective mobile connectivity

    Countless companies are facing mounting mobile connectivity costs as more and more employees require mobile devices and travel around this rapidly shrinking globe. Make sense of the available mobile connectivity options and reduce costs before they get out of control.

  • Mobile devices not so open when carriers' bottom line is threatened

    While next-generation mobile phones are more open and play nicer with third-party developers, some applications are still taboo, particularly when they intersect with service provider interests.

Do you have something to add to this definition? Let us know.

Send your comments to techterms@whatis.com

There are Comments. Add yours.

 
TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to: