Computer-Aided Design of Three-Port Waveguide Junction Circulators

The complete performance of a lossless three-port H-plane waveguide junction loaded coaxially with various inhomogeneous ferrite cylanders has been evaluated over the waveguide bandwidth and compared with experiment. Qualitative agreement between the predicted and measured performance was generally good using only the first three modes, n=0±1. It has been shown theoretically and verified experimentally that if the 4πM_s of a homogeneous rod or the internal field is increased, the circulation frequency f₀ increases; conversely, if the pemittivity is increased, f₀ decreases. These conflicting effects are modified when the magnetization 4πM_s and permittivity ε are inhomogeneous. For example, if the 4πM_s(γ) is small at the outer surface of the rod (with permittivity held constant), the effect on f₀ is very small; but if 4πM_s(spl gamma) approaches zero for γ small, then f₀ may decrease significantly. On the other hand, if ε/subγ/(γ) approaches unity near the outer surface of the rod, f₀ may increase significantly; but if ε/subγ/(γ) approaches unity near the center of the rod, f₀ is affected relatively little. The inhomogeneous structure has also shown that decreasing the ferrite volume may improve the performance, and high-power applications are suggested. With a conducting pin down the center of the ferrite, relative bandwidths of 40-50 percent are predicted.