What is a balun and how is it designed?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

A balun (balanced-to-unbalanced) converts between a single-ended port referenced to ground and a differential port whose two terminals carry equal and opposite signals. Baluns feed dipole antennas, double-balanced mixers, push-pull amplifiers and differential RF ICs, and often transform impedance at the same time.^[1]^[2]

What types of balun exist?

Magnetic (flux-coupled) transformer: wideband at HF–UHF using ferrite cores.
Transmission-line (Guanella, Ruthroff): coax or twisted pairs on ferrite; wide bandwidth, 1:1 or 4:1 ratios.
Marchand: two coupled λ/4 sections; planar, about an octave of bandwidth.
Lumped LC: lattice of Ls and Cs giving ±90° shifts; narrowband, compact.
Ceramic/LTCC chip baluns: matched to specific RF ICs.
Sleeve (bazooka): λ/4 choke on coax feeding a dipole.

What specifications matter?

Insertion loss, impedance ratio, amplitude balance (dB) and phase balance (degrees from 180°), common-mode rejection, and bandwidth. Imbalance converts differential to common mode, measured as mixed-mode S_cd.

Why do antennas need baluns?

Feeding a balanced dipole directly from coax lets current flow on the outside of the shield, distorting the pattern and causing radiation from the feed line; a choke or balun suppresses this common-mode current.^[3]

Frequently asked questions

Is a balun the same as a transformer?

Many baluns are transformers, but transmission-line and coupled-line baluns also exist.

What is a current balun?

One that forces equal and opposite currents on the balanced port, such as a common-mode choke.

Do chip RF transceivers need baluns?

Many with differential RF ports do; integrated baluns are increasingly common.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.
“The ARRL Handbook for Radio Communications”. ARRL. annual editions.
“Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.

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