In radio systems, a biconical antenna is a broad-bandwidth antenna made of two roughly conical conductive objects, nearly touching at their points. Biconical antennas are broadband dipole antennas, typically exhibiting a bandwidth of 3 octaves or more.
Omnidirectional biconical antenna
The conical conductors need not be solid cones nor infinitely long. A simple conical monopole antenna is a wire approximation of the solid biconical antenna and has increased bandwidth (over a simple monopole). A common variant is the Discone antenna, where one of the cones is replaced with a flat disk. A bowtie antenna is a wire approximation in two dimensions of a biconic dipole antenna (used, for example, for UHF television reception).
The biconical antenna has a broad bandwidth because it is an example of a travelling wave structure; the analysis for a theoretical infinite antenna resembles that of a transmission line. For an infinite antenna, the characteristic impedance at the point of connection is a function of the cone angle only and is independent of the frequency. Practical antennas have finite length and a definite resonant frequency.
Biconical (or "bicon") antennas are often used in electromagnetic interference (EMI) testing either for immunity testing, or emissions testing. While the bicon is very broadband, it exhibits poor efficiency at low frequencies, resulting in low field strengths when compared to the input power. Log periodic dipole arrays, Yagi-Uda antennas, and reverberation chambers have shown to achieve much higher field strengths for the power input than a simple biconical antenna in an anechoic chamber. However, reverberation chambers, especially, are poor choices when the goal is to fully characterize a modulated or impulse signal rather than merely measuring peak/average spectrum energy content.
Small biconical microwave antennas (up: 1–18 GHz, down: 0.5–3 GHz)
DIY DVB-T butterfly antenna, applicable in the so-called core area