Take two steps toward better circulator design

Design considerations of high power, octave-band junction circulators are presented and a two-step design method is proposed. The circulator is composed of a junction resonator comprising a transversely magnetized ferrite medium that symmetrically loads a stripline center conductor. Mathematical models of junction circulators are discussed, concluding that the correlation between theory and experiment is not adequate to permit accurate circulator design, thus the two-step method is proposed. The first step consists of selecting the ferrite material and its radius according to fundamental principles. A test fixture is designed and the ferrite junction characterized in terms of its junction admittance. The second step is to take the measured admittance and, using a computer program, synthesize an equalizing network. Following these principles a low power unit was designed and its admittance characteristics and equalizing network are presented. The minimum return loss is 17 dB while the maximum insertion loss is 0.3 dB over the 4 to 8 GHz range, which validates the two-step method.