RFTransformer

RFTransformer is a radio-frequency transformer, a passive two-port network that transfers RF signals between circuits with a defined impedance transformation and electrical isolation. It is designed to operate across a range of frequencies from a few kilohertz to several gigahertz, depending on winding geometry and core material.

An RFTransformer uses mutual inductance between its windings. The ideal impedance transformation is proportional to the square of the turns ratio (Np/Ns)^2, so choosing the turns determines the source and load impedance seen by the connected circuits. Real devices include parasitic elements that affect bandwidth and loss.

Construction methods include ferrite-core transformers, air-core designs, and planar or surface-mount variants. Variants such as baluns convert between balanced and unbalanced lines, while broadband or multilayer transformers aim to preserve impedance over wide frequency ranges. Coaxial and interleaved winding geometries are common in RF transformers.

Performance is described by frequency range, insertion loss, return loss, coupling coefficient, and self-resonant frequency. Design trade-offs involve core material, winding capacitance, leakage inductance, and physical size. Transformers for RF use often prioritize low loss and stable impedance over a specified bandwidth.

Applications include impedance matching for antennas, front-end and input networks for receivers and transmitters, isolation between stages, and matching networks for power amplifiers. They are used in radio, telecommunications, and test equipment to adapt impedances and improve power transfer.

See also: balun, impedance matching, transformer.