Coaxial antenna
A half-wave dipole antenna used as a vertically polarized omnidirectional antenna.
A coaxial antenna, often known as a coaxial dipole, is a particular form of a half-wave dipole antenna. It is most often employed as a vertically polarized omnidirectional antenna.
- Patent 1
- US patent 2,184,729 Antenna System granted December 26, 1939
- Patent 1 inventor
- Arnold B. Bailey
- Patent 2
- US patent 7,151,497 Coaxial Antenna System granted December 19, 2006
- Patent 2 inventor
- Bonnie Crystal
Lore & Background
The coaxial antenna traces its origins to a patent filed in 1937 by Arnold B. Bailey, who was granted US patent 2,184,729 on December 26, 1939, for a vertical antenna providing coaxial element sleeve structures. Later, Bonnie Crystal was granted US patent 7,151,497 on December 19, 2006, for new types of coaxial antennas with reduced size providing efficient broadband, wideband and controlled bandwidths, using radiation by the outside of the coaxial elements.
In its most basic form, a quarter-wavelength section of coaxial cable is prepared such that the inner and outer conductors are separate but still attached to the remaining cable. The outer (shield) conductor is connected to a quarter-wavelength conducting sleeve into which the cable is inserted, and the inner conductor protrudes vertically above the sleeve for a quarter-wavelength. Additional quarter-wavelength sections may be connected to the outer conductor to form a better ground plane.
Dipole antennas constructed using coaxial cables with shorted ends are often given the name 'Bazooka' dipoles.
Reader's Guide
The coaxial antenna represents a specific implementation of the half-wave dipole, notable for its use of coaxial cable elements to achieve vertical polarization and omnidirectional radiation. Its significance lies in the structural innovations introduced by Bailey and later by Crystal, which allowed for reduced size and controlled bandwidths. The design's reliance on the outer conductor of the coaxial cable for radiation, combined with the sleeve and protruding inner conductor, provides a practical method for constructing a vertically polarized antenna. The legacy of this antenna type is evident in its continued use in amateur radio and other applications where a simple, vertically polarized omnidirectional antenna is needed. The 'Bazooka' dipole variant further demonstrates the adaptability of the coaxial cable in antenna construction, offering a compact and efficient solution for radio communication.
Did You Know?
- Arnold B. Bailey was granted US patent 2,184,729 for the coaxial antenna in 1939.
- Bonnie Crystal was granted US patent 7,151,497 for reduced-size coaxial antennas in 2006.
- The basic form uses a quarter-wavelength section of coaxial cable with separated inner and outer conductors.
- Dipole antennas made from coaxial cable with shorted ends are called 'Bazooka' dipoles.
Frequently Asked Questions
What is a coaxial antenna?
A coaxial antenna, frequently called a coaxial dipole, is a specific variant of the half-wave dipole design. It is most commonly deployed as a vertically polarized omnidirectional radiator.
Who holds the key patents for the coaxial antenna?
The earliest cited patent is US 2,184,729, granted to Arnold B. Bailey on December 26, 1939, for an antenna system. A later patent, US 7,151,497, was granted to Bonnie Crystal on December 19, 2006, specifically for a coaxial antenna system.
What are the coaxial antenna's core operating characteristics?
It radiates with vertical polarization and provides omnidirectional coverage in the horizontal plane. Its electrical length corresponds to a half-wave dipole, which gives it a predictable impedance and radiation pattern.
How does a coaxial antenna differ from a standard dipole?
While both are half-wave structures, the coaxial antenna incorporates the geometry of coaxial cable into its radiating elements, making it a particular sub-type rather than a generic dipole. This construction simplifies feeding and integration into coaxial transmission lines.
Why is the coaxial antenna considered important in antenna practice?
Its combination of simple construction, omnidirectional coverage, and vertical polarization makes it a go-to choice for many practical applications. It has remained in continuous use from the late 1930s through the 2000s, as reflected in its patent history.
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