A planar phase shifter having plural layers of ferrite forming a closed magnetic toroidal path and including internal layers of dielectric material of a relatively high dielectric constant and underlying layers of dielectric material having a relatively low dielectric constant. A stripline...http://www.google.com.au/patents/US5828271?utm_source=gb-gplus-sharePatent US5828271 - Planar ferrite toroid microwave phase shifter
