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Waveguide Standing Wave Measurement

June 10th Fact-of-the-Day

Electric and magnetic fields are completely contained by a waveguide, so it is necessary to insert an electric probe or a magnetic loop inside to measure their strengths. The voltage or current standing wave ratio (VSWR or ISWR) can be measured by cutting a narrow lengthwise slot that is fitted with a small electric probe or magnetic loop that extends a short distance inside. It is important that the probe or loop extend only a short distance inside to minimize disturbances of the internal fields. The probe or loop is connected to an external RF voltage or current indicator and is slid along the length of the waveguide to obtain maximum and minimum readings. The ratio between those readings provides the voltage or current standing wave ratio. Although either a probe or loop can be used, more accurate SWR measurements generally result from use of a probe, because its physical position along a waveguide can be more precisely determined. ©2005 Martek International All rights reserved.

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