Radiation resistance

The radiation resistance is the share of the base impedance of an antenna, which is caused by the emission of electromagnetic energy. He is - similar to the characteristic impedance of a cable - determined by geometrical factors and allows a computational simplification, because the complicated fields on the feed point are calculated back in the room. He is independent of the material and does not contain constituents such as the ohmic resistance of the antenna wires.

Basics

From the standpoint of energy suppliers (generator, oscillator, amplifier, etc. ) interested seen for the energy flow only the radiation resistance at this point. On the other hand, the concept allows a separation of the effects of radiation, as well as other losses or energy storage processes. In the frequency range of the radiation resistance is a complex quantity, so there is an active component and a reactive component.

• The active component describes the beneficial effect of the energy dissipation. It is therefore not to be interpreted as a loss, such as in a resistor. In the time domain it becomes a damping term.
• The reactive part describes Energiependelungen that are visible only in the near field.

Examples

Well-known examples occur in electromagnetic waves in the antenna technology as well as the mechanical waves in acoustics ( acoustic radiation resistance).

The radiation resistance of an antenna is to think of the connection point. The load of the transmitter will then consist of the feed line which is terminated with the resistor. The complicated spatial dependence of the radiation field is expected in these and no longer directly visible.

The radiation resistance of a T antenna with a very large roof capacity is usually very small and is

The radiation resistance of a dynamic loudspeaker acts as a counter force on the diaphragm to the chassis. Compared to other mechanical forces and the electromagnetic motor forces this proportion is usually completely negligible.

The radiation resistance thus makes it possible to introduce a well-founded and well-founded approximation by exact calculation, which makes the relationship more understandable than the complete solution of the field equations in addition to the mechanical and electrical equations. Nevertheless, the radiation resistance is not purely a mathematical parameter. There is no such proportion as the chassis model, the impedance curve is not consistent with the measurements, it can therefore by varying the other parameters is not a convincing fit of the trace and the theoretical curve can be achieved.