pcb inductance

Hello everyone,

I have been wondering how to enhance mutual inductance between two distributed inductors in PCB microwave circuits? For example, we desire the inductance coupling coefficient up to 0.5. The entire structure should be as symmetric as possible, and the PCB board could be multilayer (2, 3, or 4) configuration.

I have been considering this problem for a couple of weeks, and wondering if we could obtain high inductance coupling coefficient (eg. km=0.5) in PCB microwave circuits.

Thank you for your time and efforts.