Square-Loop Garnet Materials for Digital Phase-Shifter Applications

Abstract
Materials from the garnet family 3[(1‐x) Y2O3·xGd2O3]· 5[wAl2O3· (1‐w) Fe2O3] have been investigated for use in latching‐type digital phase shifters. At room temperature, as x and w varied from 0 to 0.30, the electrical properties of these materials varied in the following manner: saturation magnetization (4πMs)−1780 to 500 G, resonance linewidth (ΔH)−33 to 200 Oe, remanence ratio Rr(Br/Bs)−0.90 to 0.65, coercive force (Hc)−0.50 to 2.00 Oe, switching constant (Sw)−0.50 to 1.00 μsec‐Oe. By proper choice of x and w, some of these properties can be made quite insensitive to temperature and power variations over wide ranges. It was found that, although Hc and Rr tend to undergo large unfavorable changes with x and w, they could be controlled by increasing the average size of the crystallites. A five‐bit (180°, 90°, 45°, 22½°, and 11¼°) phase shifter was developed using material from the above family in a square toroid geometry. This device operated across the frequency band 5.4 to 5.9 Gc/sec with a switching rate of 5 kc/sec and a maximum switching time of 1 μsec. Phase‐shift stability over the temperature range 50° to 125°F was better than 5%, losses were less than 0.80 dB and VSWR less than 1.25 across the frequency range. The unit performed equally well at peak power levels up to 10 kW and average power levels up to 300 W. The total energy required for continuous switching of the 180° bit at the above rates was slightly over 200 μJ.