Adam Abramowicz

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.

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)

Analysis of Coupled Dielectric Resonators by Means of Eigenfrequency Method

Coupled dielectric resonators are analyzed using resonant frequencies of the structures - the eigenfrequency method of coupling coefficient calculations. The method uses simple lumped elements models of coupled dielectric resonators. This models are based upon the mutual coupling concept. It is shown that different resonant modes need to be analyzed with different models. Two and three coupled resonators are investigated. Computations agree very well with the experimental results.

Exact Model of Coupled Dielectric Resonators

An exact model of coupled dielectric resonators is presented which allows accurate calculations of coupling coefficient. Contrary to previous models this one includes magnetic as well as electric type of coupling. The model is discussed on the basis of the results computed by the mode matching method. Experimental measurements are found to be in excellent agreement with the calculations. The model makes the calculation of the resonant frequencies of isolated dielectric resonators placed on an infinite metal plane possible.

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.

New model of coupled transmission lines

The paper shows that an existing description of coupled transmission lines is inconsistent and proposes a new model based truly on the mutual coupling concept. In the existing formulation a series electric coupling and parallel magnetic coupling are combined. In the new formulation the parallel electric and magnetic couplings as well as series electric and magnetic couplings are used. The obtained model of coupled lines has physical background related to the odd and even type of propagation and agrees with the practical results. >

Theory and application of circumferentially magnetized ferrites in tunable devices

The theory of tunable TE01¿ mode dielectric resonators containing circumferentially magnetized ferrites is developed. A solution of the electrodynamic problem is based on the Rayleigh-Ritz method. It is shown that such resonators can effectively operate as tunable devices with tuning range up to 2%.

Center frequency of wideband direct-coupled resonator filters

Wideband direct-coupled resonator filters with real inverters are analyzed and compared to filters based on ideal inverters (Cohns filter). Characteristic features of the wideband filters are described. A new definition of the filter center frequency based on filter frequency characteristic is proposed. Dependence of the center frequency on the filter order is presented. A new type of filter structure, new design methodology and example of 3rd order, 115% bandwidth UWB filter is presented.

Computer-Aided Design of Mechanical Tuning Structures of a Dielectric Resonator on Microstrip Substrate

Analysis of dielectric resonators mounted on microstrip substrate with tuning metal screw, tuning metal plate, and tuning dielectric disc has been presented. The radial mode matching method has been applied to calculate the resonant frequencies and the Q-factor of the above structures.

Design and realization of low cost waveguide filters and diplexers

The design method as well as realization examples of the K-band filters and diplexers are presented. In the design process the 3D electromagnetic simulations and circuit simulations are combined. The 3D simulations produce accurate results taking into account all effects resulting from CNC fabrication process like rounded corners of resonators. First the filters and other elements are analyzed and optimized separately in the 3D FDTD simulator then the complete characteristics of diplexers are obtained in the circuit simulator where the distances between the elements are optimized.