HIGH-Q SAPPHIRE-RUTILE FREQUENCY-TEMPERATURE COMPENSATED MICROWAVE DIELECTRIC RESONATORS

A sapphire-rutile composite resonator was constructed from a cylindric al sapphire monocrystal with two thin disks of monocrystal rutile held tightly against the ends. Because rutile exhibits low loss and an opp osite temperature coefficient of permittivity to sapphire, it is an id eal material for compensating the frequency-temperature dependence of a sapphire resonator. Most of the electromagnetic modes in the composi te structure exhibited turning points (or compensation points) in the frequency-temperature characteristic. The temperatures of compensation for the WG quasi TM modes were measured to be below 90 K with Q-facto rs of the order of a few million depending on the mode. For WG quasi T E modes, the temperatures of compensation were measured to be between 100 to 160 K with Q-factors of the order of a few hundreds of thousand s, depending on the mode. The second derivatives of the compensation p oints were measured to be of the order 0.1 ppm/K-2, which agreed well with the predicted values.