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Measurement of power and the standing wave ratio

Figure 1: Waveguide section of the standard WR284 with directional coupler for the S-band

Figure 1: Waveguide section of the standard WR284 with directional coupler for the S-Band
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Measurement of power and the standing wave ratio

A power measurement is possible on a radar unit if it has a passive transmitting antenna. With active phased array antennas, such a measurement is not possible because there is no central point at which to measure.

For this purpose, the manufacturer usually provides a measurement facility in the feed line to the antenna. It is often a waveguide section, which is installed shortly before the feedthrough of the radar shelter.

Usually, only a single directional coupler is installed in this waveguide section, so that the measuring procedure needs the change of measuring cable and the terminating resistor. In the waveguide section shown in figure 1 two-directional couplers are provided so that a measurement of the transmitter's power and the standing wave ratio can be made simultaneously (i.e., without changing the measuring cable).