Directional couplers are used in a wide variety of applications to sense RF power, and they may appear at multiple points in a signal chain. In this article, we will explore Analog Devices’ ADL5920, which combines a broadband directional bridge-based coupler with two rms responding detectors in a 5- × 5-mm surface-mount package. This device helps overcome the struggle that conventional discrete directional couplers deal with regarding the tradeoff between size and bandwidth, particularly at frequencies below 1 GHz.
In-line RF power and return loss measurements are typically implemented using directional couplers and RF power detectors. In Figure 1, a bidirectional coupler is used in a radio or test-and-measurement application to monitor transmitted and reflected RF power. It’s also sometimes desirable to have RF power monitoring embedded in a circuit, with a good example being where two or more sources are being switched into the transmit path (either using an RF switch or with external cables).