Biconical antenna
A broadband dipole antenna with a bandwidth of three octaves or more.
A biconical antenna is a type of broadband dipole made from two cone-shaped conductive pieces that almost meet at their tips. It can operate across a very wide frequency range—typically three octaves or more—and is commonly used in electromagnetic interference (EMI) testing, both for immunity and emissions measurements.
This antenna’s broad bandwidth comes from its traveling wave structure. In theory, an infinitely long biconical antenna acts like a transmission line, with a characteristic impedance that depends only on the cone angle, not the frequency. Practical versions have a finite length and a specific resonant frequency. A simpler version, the conical monopole, uses a wire to approximate the solid cone and offers wider bandwidth than a standard monopole.
A common subtype is the bowtie antenna, which is essentially a flattened biconical design often used for short-range UHF television reception; it is also called a butterfly antenna. Sir Oliver Lodge invented the biconical antenna.
Despite its wide bandwidth, the biconical antenna has poor transmitting efficiency at lower frequencies, producing weaker fields for the same input power compared to log periodic dipole arrays, Yagi–Uda antennas, or reverberation chambers in an anechoic chamber. However, when the goal is to fully characterize a modulated or impulse signal—rather than just measuring peak or average spectrum energy—a reverberation chamber is not suitable.
- Inventor
- Sir Oliver Lodge
- Bandwidth
- three octaves or more
- Common subtype
- bowtie antenna (also called butterfly antenna)
Lore & Background
The biconical antenna was invented by Sir Oliver Lodge. Its broad bandwidth arises because it is a traveling wave structure; for a theoretical infinite antenna, the characteristic impedance at the feed point depends only on the cone angle and is independent of frequency. Practical finite-length antennas have a definite resonant frequency. A common subtype is the bowtie antenna, a flattened version often used for short-range UHF television reception, also referred to as a butterfly antenna. A simple conical monopole antenna is a wire approximation of the solid biconical design and offers increased bandwidth over a simple monopole.
Reader's Guide
Biconical antennas, often called 'bicons,' are widely employed in electromagnetic compatibility testing, both for immunity and emissions testing. While they provide very broad bandwidth, they exhibit poor transmitting efficiency at the low end of their frequency range, resulting in lower field strengths for a given input power compared to log periodic dipole arrays, Yagi–Uda antennas, or reverberation chambers in an anechoic chamber. However, when the goal is to fully characterize a modulated or impulse signal rather than merely measuring peak and average spectrum energy content, a reverberation chamber is a poor choice for a test environment. The biconical antenna thus remains a practical tool for broadband measurements where signal characterization is important.
Did You Know?
- A common flattened subtype is the bowtie antenna, also called a butterfly antenna.
- For an infinite biconical antenna, the characteristic impedance depends only on the cone angle and is independent of frequency.
- Biconical antennas are often used in electromagnetic interference (EMI) testing.
Frequently Asked Questions
Who is Biconical antenna?
The biconical antenna traces its conceptual roots to Sir Oliver Lodge, who first explored the idea. In practice it is a broadband dipole built from two cone-shaped conductive elements that nearly touch at their narrow tips.
What are Biconical antenna's powers/role?
Its headline ability is sweeping three octaves or more of frequency in a single structure, which makes it a staple of electromagnetic interference testing. Engineers reach for it whenever they need a wide-band tool for both emissions and immunity measurements.
How does Biconical antenna achieve its wide bandwidth?
The trick is its traveling-wave geometry: in the ideal infinite-length limit it behaves like a transmission line whose characteristic impedance depends only on the cone angle, not on frequency. Practical finite-length versions approximate that behavior to deliver the ultra-broad response.
Why is Biconical antenna important in the RF world?
Because one biconical element can stand in for a stack of narrowband dipoles, it streamlines EMI test setups and cuts down compliance-measurement time. Its predictable, angle-set impedance also keeps modeling and calibration straightforward.
What is Biconical antenna's connection to the bowtie (butterfly) antenna?
The bowtie, or butterfly, antenna is a well-known subtype that shares the two-element, near-tip geometry but tapers into a flatter, wing-like profile. It inherits much of the biconical's broadband character while offering a more compact physical footprint.
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