Planar millimetric semiconductor junction circulators

Broadband circulator operation in the millimeter wave region is currently not available. Traditionally such devices require a DC magnetised ferrite material to provide gyrotropic behaviour. Broadband ferrite circulators are limited to upper frequencies of around 40 GHz due to the maximum saturation magnetisation of ferrites available. Here theoretical results are presented for a broadband semiconductor junction circulator operating up to a frequency of 120 GHz and at a temperature of 77 K. The solid-state basis for this gyroelectric behaviour is the Drude model. The gyroelectric effect arises from cyclotron motion of nearly-free electrons under the influence of an applied DC magnetic field. Comparisons are made between the regions of operation in the ferrite device and those of the proposed semiconductor device. The semiconductor device exhibits a "tracking" response with respect to the perfect circulation conditions at frequencies in the millimeter wave region. Reference is made to the complex permeability tensor of the ferrite and the corresponding permittivity tensor in the semiconductor. The assumptions made in the analysis and the likely semiconductor candidates are also discussed: these include InSb, GaAs and InAs.