Krzysztof Derzakowski

A dielectric resonator for measurements of complex permittivity of low loss dielectric materials as a function of temperature

An application of a mode dielectric resonator is described for precise measurements of complex permittivity and the 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, with relative computational accuracy of less than . The influence of conductor loss and its temperature dependence was taken into account in the dielectric loss tangent evaluation. Complex permittivities of several materials, including cross-linked polystyrene, polytetrafluoroethylene, and alumina, were measured in the temperature range of 300-400 K. Absolute uncertainties of relative permittivity measurements were estimated to be smaller than 0.2%, limited mainly by uncertainty in the sample dimensions. For properly chosen sample dimensions, materials with dielectric loss tangents in the range of to can be measured using the mode dielectric resonator.

Complex permittivity of some ultralow loss dielectric crystals at cryogenic temperatures

Whispering gallery modes were used for very accurate permittivity and dielectric loss measurements of ultralow loss isotropic and uniaxially anisotropic single crystals. Several materials including sapphire, YAG, quartz, and SrLaAlO4 were measured. The total absolute uncertainty in the real part of permittivity tensor components was estimated to be ±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.

Use of whispering-gallery modes for complex permittivity determinations of ultra-low-loss dielectric materials

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.

Comparison of split post dielectric resonator and ferrite disc resonator techniques for microwave permittivity measurements of polycrystalline yttrium iron garnet

Two techniques are evaluated for the accurate measurement of the microwave permittivity of 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 YIG permittivity from that of YIG permeability by applying a magnetic induction bias to the YIG sample under test. The SPDR method needs no special sample preparation in the case of YIG substrates, 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 two techniques improves with increasing magnetic induction bias.

Development and Investigation of an Antenna System With Reconfigurable Aperture

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.

Measurements of the complex permittivity and the complex permeability of low and medium loss isotropic and uniaxially anisotropic metamaterials at microwave frequencies

Split dielectric resonators operating in a quasi-TE011 mode were used for the measurement of the complex permittivity and the complex permeability of planar metamaterials deposited on low-loss dielectric substrates at microwave frequencies. Separation of the complex permittivity from the complex permeability for a specific metamaterial was achieved by performing measurements of the resonance frequencies and the Q-factors of a split post-dielectric resonator with two samples having different diameters but identical patterns. Measurements of the resonance frequencies and the Q-factors of empty substrates served as reference materials to determine the resonance frequency shifts and Q-factor changes due to the presence of the metamaterial only. The effective complex permittivity and permeability were determined on the basis of accurate electromagnetic modeling of the resonance structures containing the samples.

Time-Modulated Reconfigurable Antenna Based on Integrated S-PIN Diodes for mm-Wave Communication Systems

This paper concerns the study of the mm-wave reconfigurable antennas based on S-PIN diodes suitable for using in mm-wave communication systems. The investigated antennas were designed, fabricated, and subjected to the measurements in both steady and transient states. One selected antenna was incorporated into a wireless system to determine its suitability for operating in such a system as a time-modulated linear array. By means of appropriate switching of the antenna, multiple radio frequency (RF) chains were simulated in a receiver having only one RF chain. This allowed applying a combining technique for improving the system performance in a presence of a strong interfering signal.

Magnetically tunable filters for cellular communication terminals

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)

Extending Functionalities of Waveguide Slot Antennas by Means of Reconfigurable Aperture

The concept and results of investigation of some waveguide slot antenna with reconfigurable aperture have been presented in this paper. Discussed solutions have been based on the utilized semiconductor material. It allows 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, a generation of the desired shapes of radiation pattern. It allows to extend function possibilities of waveguide slot antennas compared with conventional one.

Tunable dielectric resonator bandpass filter

A simple but effective technique has been applied to magnetically tune the quasi-TE/sub 011/ mode dielectric resonator. The tuning was achieved by means of a ferrite rod situated centrally in the dielectric resonator and extending over the shield. The ferrite parameters were changed by DC magnetic field. The method assures the high quality factor of the resonator, over 3.4% tuning range and sufficiently good spurious response.