US Patent 10084224 Compensated electromagnetic coupler

An electromagnetic coupler includes a dielectric layer with a first transmission line connecting an input port to an output port. A second transmission line on another surface of the dielectric layer forms a coupled port and an isolation port. The electromagnetic coupler provides a coupled signal at the coupled port, which is representative of an input signal at the input port. The amplitude of the coupled signal is related to the amplitude of the input signal by a coupling factor. A tuning element on the dielectric layer is configured to stabilize the coupling factor over a range of variations in thickness of the dielectric layer.