25-08-2017, 09:32 PM
Measurement of Directivity and coupling coefficient and isolation of a directional coupler
Learning Objectives
To be familiar with concept of Directional coupler and its various applications in microwave circuits.
THEORY
Directional coupler:
One specific class of power divider is the directional coupler. This is a four port device that samples the power flowing into port 1 coupled in to port 3 (the coupled port) with the remainder of the power delivered to port 2 (the through port) and no power delivered to the isolated port.
Usually the isolated port is terminated within the coupler casing. In such case, the coupler appears to be a three port device. In ideal case no power is delivered to port 4 (the isolated port). Directional couplers are described by three specifications:
• Coupling © - The ratio of input power to the couple power.
• Directivity (D)- The ratio of coupled power to the power at the isolated port.
• Isolation (I) – The ratio of input power to power out of the isolated port.