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What Is a Monopole Antenna?

A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some surface, called a ground plane. The monopole is a resonant antenna, and its length is typically a quarter wavelength of the radio waves it is designed to transmit or receive. Intrigued? Discover how this simple design underpins modern communication.
T. L. Childree
T. L. Childree

A monopole antenna is basically any sort of radio transmission antenna that stands as a single column. At first glance these sorts of antennas often look like they’re just one piece, which might make them appear simpler, at least in terms of construction, to the more standard dipole antennas, which are branched with two distinctive halves. In fact there are two key components in the monopole setting, but only the pole or erect rod is visible in most cases. The second component, a ground plane, is often flat and is sometimes used to mount the pole. Monopoles are usually less expensive to build and install, and though they aren’t usually quite as powerful as other options when it comes to transmissions they can be very useful in a lot of local-area communications and receptions. Car radios use them almost exclusively, for instance, as do many cellular telephone networks, particularly in developing countries.

Antenna Basics

Man holding computer
Man holding computer

Antennas are used to transmit as well as receive electromagnetic waves, which are converted either from or to an electrical current. The same antenna can be used for both transmissions and receptions because the electromagnetic characteristics of all antennas are identical. Since antennas are typically used to transmit and receive radio waves, they are considered a key component of radio equipment. Most radios require several different pieces in order to prepare and transmit, but without a sufficient antenna their broadcasts won’t make it far from the base unit.

Most of the antennas used for broadcasting are dipole, which means that they have two poles or main branches. Monopole examples can sometimes be used for broadcasting, but more often they’re involved in the reception of signals that have been send from some more powerful station situated elsewhere.

Understanding Monopole Technology Generally

In its most basic sense, a monopole antenna is a radio antenna that is one half of a dipole antenna combined with a right-angle ground plane of considerable length in place of its other half. A dipole antenna has two halves, while a monopole model replaces one of the halves with an electrically conductive surface known as a ground plane, which behaves like the other half of a dipole antenna. With a large enough ground plane, the monopole can be as strong as its branched alternative. Automobile antennas are a common example, with the metal of the automobile itself forming the ground plane.

Main Uses

Monopole antennas can be used in a range of frequencies from several hundred kHz to a few GHz. In telecommunications terminology, a monopole usually refers to an antenna that stands alone and is self-supported or guy-wire supported, meaning it's supported by the tension of attached cables which are anchored to the ground. A group of monopoles used to manage the direction of long and medium wavelength radio frequencies is often called a directional antenna array.

Antennas are not only employed in television and radio broadcasting, but also in point-to-point communication as well. Cell phones, wireless Local Area Networks (LAN), spacecraft communication, and radar all require antennas in order to operate. The low cost and quick installation of monopole-type antennas has made them the first choice for mobile and Internet networks throughout the world, especially in developing countries.

Most Common Types

There are two basic types of monopole antennas: solid and planar. The solid type, although more expensive to manufacture, is known for having good bandwidth and being completely omni-directional.

The more commonly used and less expensive planar-type also has good bandwidth, but experiences distortion at higher frequencies, thereby making it non omni-directional. A cross-shaped, planar-type antenna has been designed and implemented in recent years that overcomes this frequency distortion while continuing to retain good bandwidth. A dual-frequency cross-shaped monopole has also been fabricated and tested in an attempt to reduce frequency distortion even further.

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