A Review of Common Line-Section Directional Couplers

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  • Author: Gary Breed
An ideal directional coupler will sample (for measurement) the forward- and reverse-moving waves in a transmission line, keeping the two directions separated, without disturbing the direct signal path through the coupler. Of course, such an ideal device is impossible, thus we have specifications that describe a coupler’s performance in each of these areas: Directivity—The degree of rejection (in dB) for the unwanted signal direction. Typical couplers may have directivities from 20 to 40 dB. Coupling—The ratio (in dB) of the incident power to the coupled power output. Higher operating power levels require higher coupling values to avoid overload of external circuitry. A higher coupling ratio typically has less effect on the through path.