EMC Question of the Week: July 9, 2018
Which of the following devices is used to connect a balanced antenna to a coaxial cable?
- impedance matching circuit
- high-pass filter
- low-pass filter
- balun
Answer
The correct answer is "d." A balun is a device that is used to interface between balanced and unbalanced signal carriers. Balanced signal carriers such as twisted wire pairs, half-wave dipoles and biconical antennas consist of two conductors that have the same impedance to ground. Unbalanced signal carriers, such as microstrip circuit board traces and coaxial cables, consist of two conductors that have different impedances to ground. When signals propagating on a conductor pair experience a change in electrical balance, mode conversion occurs and some of the signal power is reflected or lost. Baluns provide a means for interfacing balanced and unbalanced signal carriers with minimal mode-conversion loss.
Baluns can take many forms, but the most common balun is an isolation transformer with one side of the primary connected to ground. The secondary is either floating or has a center tap connected to ground. Many baluns also perform impedance matching, but the impedance matching function is independent of the balance matching function.
Have a comment or question regarding this solution? We'd like to hear from you. Email us at