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Matching the Impedance of Space

A previously-syndicated Fact-of-the-Day

Maximum power transfer from a line to a load occurs when the impedance of the load matches the characteristic impedance of the line. Where the load is an antenna, the impedance of the antenna should therefore ideally match the impedance of the line. However, the end-objective is not simply to deliver power to an antenna. The objective is to have the antenna efficiently transform power from a line into space as electromagnetic radiation. The electromagnetic impedance of space is approximately 377 ohms. If the power an antenna receives is to be transformed into space as efficiently as possible, the antenna must have a 377-ohm electromagnetic impedance at its boundary with space. Therefore, an efficient antenna is a device that converts RF power into electromagnetic radiation while transforming the impedance of a line to the 377-ohm impedance of space. ©2004 Martek International All rights reserved.

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