Impedance matching

Through impedance matching, also known as power adjustment, in high-frequency technology, the source ( output resistance ) is adjusted optimally a signal to the load ( input resistance).

In contrast, in the audio technology of the entertainment industry is the voltage adjustment, the usual adjustment. This allows the parallel connection of several actuators provide a source. The energy technology works with voltage adjustment; here is maximum efficiency in the foreground.

In the high-frequency technology loads are often complex, while almost always assumed in the data technology of real quantities.

Cause

Often a load impedance is not matched to a line, what with alternating currents of radio and high frequency technology leads to standing waves on the line, so that the full benefit can not be transferred to the load from the generator. On a line with full standing wave no energy can be transported. This effect can be with stubs or by parallel or series circuit of capacitor ( s) or inductance ( s) prevented. Such an impedance transformer to match the impedance of source or line to the load impedance.

To determine the optimum component sizes and adjusting structure, the adjustment by means of the Smith chart is simulated; see also resonant transformer and line transformation.

In practice, there are matching structures, with which one can customize any impedance to the impedance of the line: L-, T- and Pi - or structure. The name is derived from the appearance of the component assembly. Here, a coil or capacitor may be, the configurations listed below are merely exemplary in every branch. The selection of the matching structure is not only necessary from the transformation path and thus the adjustment dependent, but also from the peripheral environment.

When building particularly on a coupled to the RF line supply voltage ( DC voltage ) must be taken, which, for example a direct connection of a coil to the ground is not possible. The DC voltage must therefore be blocked by a series-connected capacitor. The greater the capacitance is, the less it influences the impedance of the operating voltage supplied to the component.

Under matching networks is one of the most popular design methods lossless L- network. This applies to real impedance adjustments.

Has an impedance and an imaginary part, as coil or capacitor, to be extended as the first complex conjugate to compensate for the imaginary part. Has a capacity of an imaginary reactance -50 Ω, it must be compensated by means of series circuit with a coil which has an impedance of 50 Ω.

For the dimensioning of the parallel element applies is parallel to the greater resistance of the source resistance and the load resistance

Consequences of two equations:

First, it is calculated from and. may be the reactance of a capacitor or a coil. The resulting reactance in must now be compensated only by the complex conjugate element.

Microstrip matching

For the higher frequency ranges from 1 GHz cable lengths have increasingly influences. This can also take advantage of to match impedances. There are open stubs and shorted stubs, which adapt impedances.

A certain distance from the lower impedance path "d" is selected so that the real part is adapted to the input impedance Z and admittance Y.

The length "l" of the stub is selected such that the reactive component of the input impedance Z and admittance Y offset and become zero.