Lumped element circulators

Several designs for the conductors in lumped element circulators have been proposed by the author and others for the purpose of attaining wideband performance or low cost. In this paper, a new approach utilizing capacitive coupling is described along with its experimental performance. In the past, only a simple model was used in the design of the circulator. Here, the imperfect coupling between conductors and the nonreciprocal filling factor are introduced into the design formulas to make them more exact. For wideband design, matching circuits with ordinary capacitors and inductors have been used in the past. In this paper, a new approach is proposed which uses a matching network in which the capacitance decreases inversely with frequency. Material with the required characteristics is shown together with measured parameters. The improvement of a circulator with capacitors made of semiconducting Barium Titanate is also shown.