Broadband directional coupler including amplifying, sampling and combining circuits

摘要

A directional coupler for r.f. power measurement utilizes a capacitive voltage divider connected to the center conductor of a length of transmission line. The output of the divider is connected to the input of a field effect transistor amplifier, which makes the divider essentially frequency independent over a wide frequency range. The outer conductor of the transmission line comprises two sections separated by a gap and connected to each other by an annular resistor permitting a current sample to be tapped. The annular resistor is disposed between two parallel circuit boards disposed in radial planes. Circuit components, including the field effect transistor amplifier are mounted on one of the boards. The output of the amplifier and the current sample are combined algebraically at a junction to provide a signal representing forward or reflected power in the transmission line.