They can also be used in a common mode choke form to prevent radiation from the cable attached to the antenna rather than the antenna. They are used in many communications applications where antenna circuits need to be matched (impedances adapted between), and balanced/unbalanced points in the circuit needs to be converted to the alternate state. These can be implemented as coupled waveguides or microstripline on printed circuit boards.īaluns are a specially optimized RF transformer to convert an RF signal from being on an unbalanced circuit to the balanced one. There are quarter wave transformers, so named because their physical length is tuned to a quarter wavelength of the center frequency of interest. Transmission line transformers are transformers implemented in equally spaced bifiler conductive windings or cabling wound around a core that can comprise of a material like ferrite, or other suitable compound, including air.
There are several types of RF transformers available. RF transformers perform all the usual tasks of general transformers except at a much higher frequency. Transformers are also used to change voltage and current ratios (step-up / step-down relates to the relative voltage change) based upon different numbers of coils on primary and secondary sides of the transformer.
Common mode noise is removed by sensing the differential voltage in the receiver. Noise that couples on subsequent balanced lines can be encouraged to couple equally, called common mode noise. Transformer outputs have no fixed reference point (one may think of the middle point of the secondary coil windings as a floating reference point), and can therefore drive symmetric loads in a circuit that is balanced (as in it is symmetric with respect to impedance). Different impedances on the two wires on the input relative to a ground unbalances the circuit and subjects it to noise voltages relative to the ground reference. They are also used when an AC voltage on the input needs to be de-referenced from its input impedances, typically referred to as a ground level. Transformers are used in applications where the signal needs to be changed from one impedance to another.
RF Transformers are transformers that are optimized for very high frequency signal applications. Transformers couple in proportion to the magnetic permeability of the core material through which the magnetic field is changing that links the two coils, and are usually extremely efficient when used within their design windows. The coupling is caused by the varying magnetic field inducing an electromotive force (EMF) in the other conductor, often referred to as a winding or coil. An RF transformer is an electromagnetic device that sits between two or more circuits and uses changes of electric signals and the principle of induction in a conductor to produce a varying magnetic field (flux) that couples energy through to another conductor.