Types of Omni-Directional Antennas

Internet routers use omnidirectional antennas to broadcast and receive signals.

An omnidirectional antenna is used in radio communication to radiate or receive signals equally in a 360-degree radiation pattern. It is also called a "non-directional" antenna since it doesn't favor any particular direction like directional antennas that broadcast and receive signals in a single direction. There are four basic types of omnidirectional antennas that use the E plane (horizontal) and H plane (vertical).

Horizontally Polarized Antennas

Horizontally polarized antennas are used for both short- and long-range applications and are known as “loop” antennas. Small loop (short-range) antennas have a smaller radiating resistance that causes a weaker signal than other omnidirectional antennas. They are usually used on applications where antenna efficiency is not as important, such as in pagers. Larger loop (long-range) antennas can help address the inefficiency problem; however, they also decrease the distribution of current. Citizen Band radios used for ground-air and ship-shore applications are common examples of long-range applications.

Vertically Polarized Antennas

Vertically polarized omnidirectional antennas can be used for both short-range and long range applications, such as intelligent traffic applications that control traffic and check speed cameras. This type of antenna transmits an electromagnetic wave with the E field that is perpendicular to the Earth's surface and is useful for tracking and managing containers, enabling short-range meshed networks for cellphones and maximizing wireless repeater systems for broadband connections.

Multimode Antennas

Multimode antennas are used when different services are needed for the same antenna and each needs its own frequency strength, such as cars that provide a tracking system for the vehicle and mobile phone capabilities. Its electromagnetic horn type is made up of two or more modes of antenna that create nearly identical E and H plane radiation patterns, eliminating the need for two separate antennas.

Rotatable Antennas

Rotatable antennas are desirable in situations where high-power communication between a fixed station and a mobile one is needed. Possible applications for this feature include communication between shipping stations and their ships, air traffic control stations and military deployments where communication is essential between a base and a tactical unit. The distance and frequency strength needed in each of these examples varies, and a rotatable antenna creates flexibility in these situations so communication channels remain open.

References

• Encyclo: Multimode Antenna
• Short Range Log-Periodic Antenna Model 530
• The Truth about Horizontaly Polarized Antennas
• Making a Homemade Omnidirectional Antenna
• Dual Polarized Omnidirectional Antenna
• The Truth about Horizontaly Polarized Antennas
• Joe Carr's Radio Tech-Notes: Directional or Omnidirectional Antenna?
• Small Business Innovation Research: Broadband HTS Parametric Multimode Antenna for VHF/UHF Applications
• WLAN Antennas: Wireless Antenna Terminology