The Identification of Modal Resonances in Ferrite Loaded Waveguide Y-Junctions and Their Adjustment for Circulation

T h e waveguide Y-junction circulator was first introduced by H. N. Chait and T. R. Curry in 1959.1 During the past ten years it has become a widely used device. Surprisingly, its exact mode of operation has never been clearly understood. Numerous analyses and theories have been proposed for the device, but none has proven entirely satisfactory. A fundamental theory for t h e circulator in terms of its external properties was first presented by B. A. Auld in 1959." He showed t h a t the junction scattering matrix was characterized by three eigenvalues which had to be phase displaced by 120 degrees for circulation. T h e theory, however, did not show how this displacement was to be achieved since this required a more detailed field theory analysis of the junction involved. Such an analysis for the stripline circulator was first carried out by H. Bosma in 1962. 3 Based on Bosnia's results, C. E. F a y and R. L. Comstock in 1905 presented a simplified " t w o resonant mode" theory for the stripline device together with experimental evidence of the validity of their approximations. 4 This theory was later improved by W. H. von Aulock and F a y in 1968. 5 For lack of a suitable alternative, 595