Microstripline ferrite devices using surface field effects for microwave integrated circuits

Resonance isolators operating at
X
-band frequencies have been constructed in conventional 50-ohm microstripline by positioning ferrite strips on the surface of the alumina substrate adjacent to the stripline conductor. A transverse external magnetic field is applied in the plane of the surface to obtain the necessary Kittel resonance condition. It is shown that by suitable choice of ferrite dimensions the performance may be optimized to give a forward loss of 0.5 dB together with a reverse loss in excess of 30 dB at resonance. The influence of saturation magnetization of the ferrite as well as relative permittivity of the substrate material has also been examined. Nonreciprocal phase shift may be obtained by using this geometry; but high external field is required to saturate the ferrite. A modification employing an all-ferrite substrate, which may be used to design a phase shifter operated at remanence, is described.