Biconical EMC Antenna
Image of the Biconical EMC Antenna.

The EMC wire biconical antenna (also commonly known as the wire, skeletal or phantom biconical), is the most common configuration for EMC measurements in use between 20 and 300 MHz, with either conical log spirals or LPDAs used from 200 MHz to 1 GHz.

Although the antenna performs less than optimally in the low frequency range of operation that is often claimed, it has attained universal acceptance in the EMC industry. By using a standardised design based on MIL-STD 461 (U.S. Military Standard), repeatable measurements can be ensured.

The EMC wire biconical operates like a dipole antenna, but the skeletal assembly approximates a conic surface (similar to a bicone), resulting in stable impedance over a wide frequency band. The EMC wire biconical requires a balanced feed, and a balun should be used between antenna and transmitter/receiver.

The biconical EMC antenna with typical radiation pattern shown at (a) fmin, (b) 2fmin, (c) 3fmin, (d) 5fmin and (e) 10fmin.

The antenna is vertically polarised, and - although the radiation pattern of the antenna changes significantly with frequency - remains omnidirectional and rotationally symmetric in any horizontal plane.

As shown in the figure on the right, the basic antenna (where no matching or balun is used) provides a reflection coefficient below -10dB at frequencies more than double the minimum operating frequency typically quoted for EMC applications.

Typical reflection coefficient versus frequency with no matching or balun included in a 150 Ohms system.