Development of Microwave Ferrites and Garnets for Prototype Ferrite Circulators at 352 MHz & 700 MHz

The high-power RF systems for the proposed high power Proton Linac at RRCAT, India, require highpower circulators at 352 MHz and 700 MHz to protect CW klystrons from reflected power. To meet these requirements, microwave garnet and spinel ferrite development have been undertaken for high power circulators. Gd doped yttrium iron garnet (YIG) and Bi doped calcium vanadium yttrium iron garnet (CVG) materials have been extensively studied and their magnetic properties are optimized. An excellent temperature stability of magnetization (4πMS) combined with desired Curie temperature (TC >250°C) is optimized in Bi-CVG and Gd-YIG.

Curie temperature is further improved to ∼390°C with a room temperature 4πMS of ∼1080 Gauss by optimizing Al3+ substituted nickel ferrite. Large Bi-CVG ferrite disks have been developed using conventional ceramic techniques. A prototype stripline circulator has been developed for testing of ferrite resonator and optimization of design. An excellent result with low insertion loss (< 0.2 dB) and high isolation (>25 dB) at 352 MHz has been achieved.