A dipole is a type of antenna that has two poles, also called elements, with one end of each pole positioned close to one end of the other. The most familiar type of dipole is the rabbit ear antenna used with televisions. A wire dipole antenna is essentially the same, with the exception that the two poles are made of two pieces of wire rather than the metal rods like a set of rabbit ears. Wire dipole antennas can be used to receive many different types of radio transmissions, such as television, radio or shortwave signals, with the overall length of the two poles determining the antenna’s peak efficiency for a given frequency.
In terms of antenna operation theory, the wire dipole is among the more straight forward types of radio frequency antennas because of its simplicity of operation and the fact that it is constructed of nothing more than two lengths of wire. Tuning a wire dipole antenna to a specific frequency is also a simple matter, requiring nothing more than cutting a given length of wire. The most common method of determining the proper length of wire for the antenna is to cut a wire that is 95% of one half of the wavelength of the frequency to be received, then cut that wire in half to make the two poles of the antenna. Due to this fact, they are often referred to as half-wave antennas. Because these antennas are only half the length of a full-wave antenna, they take up much less space and are easier to build.
Besides being easier to construct, wire dipole antennas are also easier to take down and relocate than antennas made of more rigid materials, which may also require a supporting structure. This allows potentially very large wire dipole antennas to be built and deployed very easily almost anywhere and, if the situation calls for it, taken down and moved just as easily. The small size needed for high frequencies also makes these types of antennas small enough to put in the most convenient of spaces, such as those placed inside the windshield of a car for an FM radio antenna.
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While wire dipole antennas are more efficient than mono-element models, such as whip-style antennas, they are not as efficient and versatile as other, more ridged, dipole antennas. The primarily reason for this is due the diameter of the wire when compared to the much larger diameter of the metal elements of ridged antennas. Ridged dipole antennas can also have more elements added parallel to the dipole elements to serve as directors and reflectors, which can greatly improve performance. Wire dipole antennas are simply too narrow to align with other elements effectively.