Cooled, ultrahigh Q, sapphire dielectric resonators for low-noise, microwave signal generation

Abstract

Ultra-high Q, X-band resonators, used in a frequency discriminator for stabilization of a low-noise signal generator, can provide a means of obtaining significant reduction in phase noise levels. Resonator unloaded Qs on the order of 500 K can be obtained in sapphire dielectric resonator (DR) operating on a low-order (i.e. TE(01)) mode at 77 K and employing high-temperature superconducting (HTS) films installed in the DR enclosure covers. Rigorous analysis for the determination of resonator frequency, modes, and unloaded Q have been carried out using mode matching techniques. Trade-off studies have been performed to select resonator dimensions for the optimum mode yielding highest unloaded Q and widest spurious mode separation. Field distributions within the resonator have been computed to enable practical excitation of the required mode. The results of both analysis and prototype device evaluation experiments are compared for resonators fabricated using enclosures consisting of conventional, metal sidewalls and covers employing HTS films as a function of cover conductivity.

Enhancement of thermal Casimir-Polder potentials of ground-state polar molecules in a planar cavity

“…A higher reflectivity could hence be obtained by using materials with very small dielectric loss. One example of such a Bragg mirror could be alternating layers of vacuum and sapphire, which can have an extremely low loss tangent (Im ε/Re ε ≃ 10 −5 and 10 −7 at room temperature and 77K, respectively [41]) combined with a refractive index considerably larger than unity (Re ε ≃ 10 [42]). Using the approximative values ε sapph = 10 + 10 −4 i at 300K and ε sapph = 10 + 10 −6 i at 77K, we have computed the reflection coefficients of the vacuum/sapphire mirror as displayed in the lower panel of Fig.…”

Invited Article: Dielectric material characterization techniques and designs of high-Q resonators for applications from micro to millimeter-waves frequencies applicable at room and cryogenic temperatures

“…1, 2 Also, to realize precise time and frequency references, it is necessary to design microwave sources with high spectral purity and precise frequency stability. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] These characteristics are directly related to the quality of the resonant element, such as cryogenic sapphire oscillators (CSOs), which are based on ultra-high-Q-factor (∼10 9 ) sapphire DRs. These oscillators are used as a secondary frequency reference and are only oscillators of pulsing a primary standard (caesium fountain clock) at the quantum noise limit.…”

Low-Noise Microwave Resonator-Oscillators: Current Status and Future Developments

“…The oscillator phase noise is reduced by applying a correction signal from the output of the frequency discriminator to the varactor phase shifter inside the loop. Many researchers have implemented designs to reduce the oscillator phase noise [13,14,15,16,17,18,19,20]. Using this technique, the phase noise of a room-temperature X-band FET oscillator based upon the low-order mode dielectric resonator was reduced to −120 dBc/Hz at 10 kHz Fourier frequency [15].…”