Application of a Tunable Dye Laser to Plasma Diagnostics in a Helium Plasma.

An equivalent circuit including the stray reactances of a microstrip-type lumped-element circulator is derived to establish the design procedure, and it is shown theoretically that a broadband circulator with a 30% bandwidth can be realized. Additionally, to obtain the broadband characteristics over a wide range of temperatures, the necessary temperature coefficients of ferrite materials and magnets are calculated. A new ferrite material with a low temperature coefficient, as well as a new fabrication process for thin-film crossovers, has been developed. The experiments indicate that a radial magnetizing field improves the circulator characteristics in both bandwith and loss. An experimental circulator exhibits the following characteristics over a wide temperature range from -10 to 60 C: VSWR less than 1.2, loss less than 1.0 dB, and isolation greater than 20 dB over a bandwidth of 450 MHz centered at 1.7 GHz.