High temperature superconductor (HTS) shielded dielectric resonators (DR's) have demonstrated to provide quality factors Q between 5/spl times/10/sup 5/ and several 10/sup 6/ at frequencies up to 20 GHz and levels of dissipated RF power in the range of watts. As dielectric materials, high purity single crystals of sapphire, LaAlO/sub 3/, and rutile exhibit sufficiently low microwave losses. There are two main areas of application which are considered to benefit from HTS-shielded DR's, namely low-phase-noise oscillators for radar systems and digital communication, and high-power filters for satellite communication. Projections for phase noise are -145 dBc/Hz at 1 kHz offset from the carrier frequency, a value of -110 dBc/Hz at 1 kHz was measured recently for an oscillator with a carrier frequency of 5.6 GHz. Modeling of filters based on resonators with Qs in the 10/sup 9/ range indicates their ability to reduce the RF power dissipation apparent in the output multiplexers of communication satellite payloads. Presently, schemes for resonator coupling and tuning while maintaining high Qs are under development.

Properties and applications of HTS-shielded dielectric resonators: a state-of-the-art report

We present an efficient algorithm to determine the resonant frequencies and the normalized modal fields of arbitrarily shaped cavity resonators filled with a lossless, isotropic, and homogeneous medium. The algorithm is based on the boundary integral method (BIM). The unknown current flowing on the cavity wall is considered inside a spherical resonator, rather than in free-space, as it is usual in the standard BIM. The electric field is expressed using the Green's function of the spherical resonator, approximated by a real rational function of the frequency. Consequently, the discretized problem can be cast into the form of a real matrix linear eigenvalue problem, whose eigenvalues and eigenvectors yield the resonant frequencies and the associated modal currents. Since the algorithm does not require any frequency-by-frequency recalculation of the system matrices, computing time is much shorter than in the standard BIM, especially when many resonances must be found. >

A new boundary integral approach to the determination of the resonant modes of arbitrarily shaped cavities

An all-cryogenic oscillator consisting of a frequency-tunable sapphire resonator, a high-temperature superconducting filter and a pseudomorphic high electron-mobility transistor amplifier was designed for the K-band frequency range. The high quality factor of the resonator above 1 000 000 and the low amplifier phase noise of approximately -133 dBc/Hz at a frequency offset of 1 kHz from the carrier, gave oscillator phase-noise values superior to quartz-stabilized oscillators at the same carrier frequency for offset frequencies higher than 100 Hz. In addition to low phase noise, the oscillator possesses mechanical and electrical frequency tunability. We have implemented a two-step electrical tuning arrangement consisting of a varactor phase shifter integrated within the amplifier circuit (fine tuning by 5 kHz) and a dielectric plunger moved by a piezomechanical transducer inside the resonator housing (coarse tuning by 50 kHz). This tuning range is sufficient for phase locking and for electronic compensation of temperature drifts occurring during operation of the device employing a miniaturized closed-cycle Stirling-type cryocooler.

Design and characterization of an all-cryogenic low phase-noise sapphire K-band oscillator for satellite communication

Large ratios of extreme nonzero conductivities in eddy current problems cause poor conditioning, due to the kernel of the curl-curl operator. Solutions to this problem (wrongly blamed on edge elements by some) are discussed.

"Stiff" problems in eddy-current theory and the regularization of Maxwell's equations

High temperature superconductor (HTS)-shielded dielectric resonators with Q-values >10/sup 5/ at T=77 K are promising candidates for applications in low phase noise oscillators. We have investigated feedback-oscillators at 5.6 and 10.2 GHz and are currently setting up an oscillator at 23 GHz. To achieve ultimate e-values we have used TE/sub 01/spl delta/-/ and whispering gallery mode resonators with the central dielectric made from sapphire or lanthanum aluminate (LaAlO/sub 3/). Employing commercial MESFET-amplifiers we have determined the phase noise performance of feedback oscillators at these frequencies. These results confirm the superior performance of HTS-shielded dielectric resonator stabilised oscillators. The long term stability of the oscillator is mainly determined by the temperature stability of the resonator frequency. Thermally induced variations of the permittivity E of the central dielectric puck cause frequency drifts of the resonator frequency. Rutile has successfully been used to build resonators with frequency stabilities <0.3 ppm/K at 5.6 GHz. To enable accurate positioning of the oscillator frequency we have investigated the effect of varying the distance between the central dielectric and a superconducting end plate for a whispering gallery mode resonator at 23 GHz. We have also started utilising a Stirling-type miniature cooler to cool the resonators. We present data on the influence of cooler vibrations on the purity of the oscillator frequency.

Temperature compensated high-Q dielectric resonators for long term stable low phase noise oscillators

An overview is presented of the MAFIA group of fully three-dimensional computer codes for solving Maxwell's equations by the finite integration algorithm. The codes are well established. Extensive comparisons with measurements have demonstrated the accuracy of the computations. The latest additions include a static solver that calculates 3-D magnetostatic and electrostatic field and a self-consistent version of TBCI that solves the field equations and the equations of motion in parallel. Work on new eddy-current modules has started, which will allow treatment of laminated and/or solid iron cores by low-frequency current. Based on experience with the present releases 1 and 2, a complete revision of the whole user interface and data structure has begun that will be included in release 3. >

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Status and future of the 3D MAFIA group of codes

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Status and future of the 3D MAFIA group of codes