DEVELOPMENT OF HELICAL PHASE-SHIFTERS.
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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A latching phase shifter was developed which makes use of a shielded helix as the microwave circuit. A ferrite tube placed inside the helix is circumferentially magnetized by passing a current through a single wire placed along the axis of the tube. The phase-delay of an RF wave on the helix depends on the sense and magnitude of the circumferential magnetization of the ferrite tube. Positive and negative switching current pulses magnetize the ferrite to remanence in either of the two senses, and result in a differential phase-delay of the RF wave. The slow-wave helix considerably reduces the ferrite volume required for a phase change of 360 degrees, and the microsecond switching times are readily achieved with very low switching power. A theoretical model for the dominant nonlinear mechanism is proposed and analyzed and the results are correlated with experimental data. Using these results, high peak power phase-shifters were designed and tested at L- and S- band frequencies. For high average power capability, the ferrite must be cooled the resulting thermal design problems are discussed. The choice of both ferrite and dielectric materials for L- and S-band frequencies are discussed with the emphasis placed on commercially available materials.