Ultimate performance limitations of high-power ferrite circulators and phase shifters

The power-handling capability of circulators and phase shifters in rectangular waveguide is analyzed. It is shown that an appropriate measure of the suitability of microwave ferrites for high-power applications is given by the "high-power figure of merit"
F_{hp}* = 4\piM\gamma^{2}h_{crit}/\omega^{2}\mu''
. Here γ is the gyromagnetic ratio, h
crit
the critical RF field, ω the (angular) frequency,
\mu"
the imaginary part of the diagonal component of the permeability tensor. In applications to nonlatching devices,
M
is the saturation magnetization; in applications to latching devices it is the remanent magnetization. The figures of merit of various rare-earth substituted garnets are reported. The figures of merit obtained to date are approximately 2. Theoretical analysis indicates that significantly larger figures of merit can be Obtained only at the cost of reducing the saturation magnetization. It is concluded that for circulators using the
H
-plane configuration and having an insertion loss of 0.5 dB the maximum attainable peak power level is of the order of 50 MW. For latching twin slab phase shifters (
E
-plane configuration) having an insertion loss of 1 dB the maximum attainable peak power level is estimated to be 80 kW.