Directional coupler

摘要

In a directional coupler, even when parasitic inductance exists, an increase in device size can be suppressed while obtaining good isolation characteristics. A transmission line type directional coupler includes a main line and a sub line that is coupled to the main line through electric field coupling and magnetic field coupling. The main line includes a signal input port and a signal output port, and the sub line includes a coupling port and an isolation port. A series capacitor is connected to only one of the signal output port and the coupling port.

主权项

1. A directional coupler comprising:
a main line including a signal input port and a signal output port; and a sub line that includes a coupling port and an isolation port and that is coupled to the main line through electric field coupling and magnetic field coupling, wherein a series capacitor is connected to only one of the signal output port and the coupling port, wherein the signal output port includes a first parasitic inductance and the coupling port includes a second parasitic inductance, and a capacitance value Cx of the series capacitor is determined as follows: for a capacitance value C1 that would cause resonance with the first parasitic inductance at a desired frequency and for a capacitance value C2 that would cause resonance with the second parasitic inductance at the desired frequency, the capacitance value Cx of the series capacitor is set smaller than or equal to the capacitance value C1 or smaller than or equal to the capacitance value C2.