Whispering-gallery modes are used for very accurate permittivity, dielectric loss, and temperature coefficient of permittivity measurements for both isotropic and uniaxially anisotropic dielectric ...materials. The relationship between resonant frequencies, dimensions of the resonant structure, and permittivity of the sample under test is calculated with a radial mode-matching technique. The relative accuracy of these computations is better then 10/sup -4/. The influence of conductor losses on dielectric loss tangent determination is treated for both whispering-gallery-mode and TE/sub 01/spl delta//-mode dielectric-resonator techniques. Two permittivity tensor components of sapphire and their temperature dependence were measured from 4.2 to 300 K. The total uncertainty in permittivity when use is made of whispering-gallery modes was estimated to be less than 0.05%. The uncertainty was limited principally by uncertainty in sample dimensions. Experimental and calculated resonant frequencies of several whispering-gallery modes differed by no more than 0.01%. The dielectric loss tangent of sapphire parallel and perpendicular to its anisotropy axis was calculated to be less than 10/sup -9/ at 4.2 K. The permittivity and dielectric loss tangent of a commercially available low-loss high-permittivity ceramic material has also been measured at S- and C-band frequencies using a large number of whispering-gallery modes.
The concept and results of investigation of a waveguide slot antenna with reconfigurable aperture is presented. Solutions are based on the utilized semiconductor material, which allows one to design ...the electronically reconfigurable antennas. The key element of the reconfigurable antenna is a surface PIN (SPIN) diode whose conductivity changes proportionally to the plasma density. SPIN structures can be activated selectively and cause, in turn, the generation of the desired shapes of radiation pattern. It allows one to extend the function possibilities of waveguide slot antennas compared with the conventional one.
Magnetically tunable two-pole dielectric-resonator filters containing axially and circumferentially magnetized ferrite elements have been designed and investigated. Employing axially magnetized ...ferrites, a 20-MHz tuning range was obtained. The Q factor of resonators was 2500 and the tuning power was 1.8 W. Filters containing circumferentially magnetized discs demonstrated a 12-MHz tuning range with the Q factor over 8000 (tuning power 3.5 W) and 28 MHz with the Q factor 3500 (tuning power 3.5 W)
An application of a TE\+v\01\#d\\-v\ mode dielectric resonator is described for precise measurements of complex permittivity and thermal effects on permittivity for isotropic dielectric materials. ...The Rayleigh - Ritz technique was employed to find a rigorous relationship between permittivity, resonant frequency, and the dimensions of the resonant structure. Complex permittivities of several materials, including cross-linked polystyrene, polytetrafluoroethylene, alumina and a ceramic material, were measured in the temperature range 300-400 K. Absolute uncertainties of relative permittivity measurements were estimated to be smaller than 0.2%. (Original abstract - amended)
Whispering gallery modes have been used for very accurate permittivity and dielectric loss measurements of ultralow loss isotropic and uniaxially anisotropic single crystals. Several materials, ...including sapphire, yttrium alumina garnet (YAG), quartz, and SrLaAlO\+v\4\-v\ were measured. The total absolute uncertainty in the real part of permittivity tensor components was estimated to be plus or minus 0.1%, limited principally by the uncertainty in sample dimensions. Imaginary parts of permittivities were measured with uncertainties of about 10%, limited by the accuracy of Q-factor measurements of whispering gallery modes. It has been observed that, for most crystals, dielectric losses can be approximated by a power function of absolute temperature only in limited temperature ranges. At temperatures between 4-50 K, losses are often affected by impurities which are always present in real crystals. (Original abstract)
For the original paper see ibid., vol. 44, no. 6, p. 848-853 (1996). In the above paper is presented a simplified, but quite accurate, method for the calculation of the resonant frequencies of ...whispering gallery modes in dielectric resonators. Abramowicz et al. have compared the result obtained by the author with the results of the full-wave radial mode-matching method, finding very good agreement. However, a part of the paper describing a model of coupled resonators and, particularly its solution were, in the commenters' opinion, faulty.
A dielectric resonator technique has been developed for measurements of conductivity and surface resistance of thin metal films deposited on a dielectric substrate. This technique allows for ...measurements of films having surface resistances that are smaller than 5
Ω without requiring the need to perform measurements of the substrate thickness. The uncertainty of the surface resistance measurements is about 2–3% for both thin films and bulk materials. The accuracy of the conductivity measurements of the thin films is similar to the accuracy of the measurements of their thickness. Several samples have been measured having thicknesses that range from 66
nm to 50
μm.
Electronically tunable dielectric resonators operating at frequencies of about 2 GHz containing axially and circumferentially magnetized ferrite elements have been investigated. Employing axially ...magnetized ferrites, a 40 MHz tuning range was obtained with Q-factor greater than 3000. For such structures the tuning speed of the order of milliseconds was achieved using helical enclosure of the dielectric resonator instead of a metal cavity. Resonators containing circumferentially magnetized ferrites were constructed whose resonant frequencies can be switched by short current pulses between two stable values that differ in frequency up to 15 MHz.
Two techniques are evaluated for accurate measurement of the complex microwave permittivity of a very soft magnetic material, polycrystalline yttrium iron garnet (YIG), at frequencies between 5.5 and ...12.5 GHz: split post dielectric resonator (SPDR); and ferrite disc resonator (Courtney). Both techniques separate permittivity from permeability by applying a magnetic induction bias to the YIG sample under test. The SPDR method needs no special sample preparation, whereas the Courtney method requires the grinding of rods from bulk YIG. The Courtney measurements of the YIG real permittivity are found to be higher on average than SPDR measurements. Agreement between the techniques improves with increasing magnetic induction bias. (Original abstract)
Electronically tunable dielectric resonators and filters operating at frequency about 2 GHz containing axially magnetized ferrite elements have been investigated. Employing axially magnetized ...ferrites 40 MHz tuning range was obtained with Q-factor greater then 3000. For such structures tuning speed of the order of milliseconds was achieved. The measurements of the trial narrow band filter showed 18 MHz bandwidth at 2.2 GHz without degradation of the RL characteristic and losses lower than 0.8 dB.
