Coaxial Ferrite Phase Shifter for High Power Applications

The low- and high-power behavior of a coaxial ferrite-loaded transmission line has been studied experimentally at microwave frequencies. Longitudinal magnetic biasing fields both above and below the cutoff range (ω/γ−4πMs≤Hdc≤ω/γ) were explored, the two regions yielding devices with markedly different characteristics. The mechanical structure consisted of a rigid ⅞-in. coaxial line fully loaded with Trans-Tech 1–103 ferrite together with appropriate quarter-wave dielectric transformers. (1) Operation below cutoff (0≤Hdc<ω/γ−4πMs), f=3080 Mc: These parameters permit construction of a compact, light-weight phase shifter producing 360° of phase shift in 10 in. of active length upon application of only 100 oe. Approximate values for hcrit are determined from the measured threshold powers and plotted versus applied field. (2) Operation above resonance (Hdc>ω/γ), f=1350 Mc: With these parameters, a device can be built that is capable of handling at least several hundred kilowatts of rf peak power while maintaining a figure of merit of 1000 or more. The loaded coaxial line provides 360° of phase shift in 24 in. of active length when biased from 950 to 1350 oe. The high-power and loss characteristics of the latter device permit application to electronic steering of the transmitter beam in a linear array antenna where relatively few phase shifters suffice. The low-field device is suited for beam control in a planar array where large numbers of relatively small phase shifters of medium peak-power capability are needed.