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What Is a Biconical Antenna?

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  • Written By: Mal Baxter
  • Edited By: Daniel Lindley
  • Last Modified Date: 26 October 2016
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A biconical antenna is a conductor that can send and receive signals from two cone-shaped element arrays that extend opposite one another. It is typically hourglass shaped, as both conductors have a common axis and balun. These broadband dipole antennas operate in ranges from 30 to 300 megahertz (MHz), though ranges from 20 MHz to 3 gigahertz (GHz) are possible. They may have bandwidths of three or more octaves.

Biconical antennas, sometimes called bicons, are essentially two cones touching points with a common central axis. Each cone applies excitation at its vertex, or point. These components may be driven by electronic charges, potentials, or alternating magnetic fields and currents at the vertex. When only one cone is angled into a plane, or at 180 degrees, it is referred to as a discone.

Available as small, large, portable, or fixed antennas, bicons are typically constructed of conductive elements that fan out of a balun. A balun, short for balance/unbalance, is a transformer coupling that converts current balances to regulate impedance, which refers to the relationship between current, voltage, resistance, and their effects on the antenna's radiation profile. The balun helps determine radiation pattern and the antenna's efficiency. The elements radiate symmetrically from their mount, although cylindrical and star-shaped varieties exist.

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Often, the biconical antenna is employed in testing electromagnetic interference (EMI), immunity, or emissions testing. These tests occur at 25-200 MHz for commercial applications and 30-200 MHz for military. Dipole and Yagi arrays indicate higher field strengths than a simple biconical antenna; the bicon is less efficient but possesses a broadband range. Simple conical monopoles and bowtie antennas, wire approximations of the biconical type, have increased bandwidth over monopoles. High-gain antennas usually have increased signal strength, whereas low-gain varieties like the bicon transmit over a wider angle.

With conductors radiating from a central point in opposite directions, the design makes the biconical antenna well suited for conducting sweep measurements and compliance testing. It's also beneficial for servicing automated antenna measurement systems. Its advantage over measurements of vertical site attenuation, or signal loss, is attributed to its long dipole element lengths at lower frequencies: for example, 16.4 feet (about 5 m) at 30 MHz.

Some designs permit both vertical and horizontal attenuation measurement sweeps. The bicon's symmetrical design allows for more consistent test repetitions, because the antenna is not affected by which way it's turned. With such applications, manufacturers will sometimes provide calibration data for measurement standards; for example, gain and antenna factor versus frequency.

Typically, the radiation pattern of a biconical antenna appears similar to that of dipole antennas, with a field pattern extending in opposing dual lobes. These patterns function virtually independently of frequency. Common applications include use in areas that require omnidirectional radiation, as well as in emission test facilities; they perform duty on ground and mobile platforms, and in aircraft. Smaller sizes permit versatile portable uses, as these antennas tend to be low weight and easily set up.

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