Dietmar Köther

Characterization of low dielectric constant materials

Materials with low dielectric constants offer great chances for applications were losses, low thermal influences and phase stability are important. One of these applications is earth observation by SARs. Syntactic foams is a promising material but its properties with respect to homogeneity are not well investigated. A new method provides qualitative characterization with good geometrical resolution.

Analysis of higher order modes on unilateral finlines with arbitrarily located slots

In this paper a rigorous method is presented which allows a complete calculation of all modes existing on a unilateral finline with an arbitrarily located slot. Also an investigation of the field distribution is possible. Hereby the behaviour of the different modes can be explained. This method also permits the determination of the propagation properties of higher order modes; thus information is needed for the calculation of finline discontinuities.

Higher order modes on usual waveguides

In the following paper some different kinds of microwave guides will be inspected under main aspect of higher order modes. The knowledge of these modes is important for field matching problems at discontinuities and for suppressing propagation of higher order modes by geometrical variations. In some cases it is sufficient to know their principal behaviour. They will be calculated in paper by the often used orthogonal expansion. This method allows to determine all kinds of waves: propagating, damping and complex waves. The following guides are inspected:1.rectangular waveguides,2.circular waveguides,3.L-shaped waveguides,4.double ridged rectangular waveguides,5.unilateral finlines with one slot,6.unilateral finlines with two slots,7.shielded microstrip lines,8.circular image guides,9.rectangular waveguides with dielectric slab,10.H-guides.

Design of circular arc finline tapers

The aim of this paper is the development of a technological simple procedure for the fabrication of tapers in finline technique with a high transmission and low reflection characteristics. This method employs tapers between rectangular waveguides and finline sections or between two electrically different waveguides in form of circular arcs which are matched to the required lapse of the slot width as a function of the characteristic impedance. The appicability of this method assumes that the transmission properties of the considered finline are known. Several examples show the feasibility of the method.

New methods for the characterization of thin dielectric samples at low frequencies

For many applications the knowledge of the dielectric properties of substrates and covers is absolutely necessary. At higher frequencies or for thicker samples many methods can be used. But, for thin dielectric sheets without metallization the characterization becomes complicate. The new approach presented here makes use of the low capacitance of a very simple set-up. This capacitance is the coupling element between two resonators with slightly different resonance frequencies. These coupled resonators are very sensitive to small changes of the capacitance value which is proportional to the dielectric constant of the investigated material.

Influence of mobile communication signals on pacemaker operation

It is well-known that mobile terminals may cause problems in the electronically system of aircrafts. But is it also possible that such signals affect function of pacemakers? To investigate these potential influences the coupling of mobile communication signals into a heart electrode and the sensitivity of pacemakers to those signals was determined. Several implantation configuration of the heart electrode, about 100 different types of pacemakers and different mobile standards (GSM, DECT, W-CDMA) were considered. The combination of electrode, pacemaker and signal offers an easy estimation of risk for different scenarios.

A generalized theory for asymmetrical coupled lines

A method that calculates the properties of geometrically or electromagnetically asymmetrical coupled lines is discussed. Analogous to the normally used theory of even and odd modes, the electromagnetic fields on the computer are described in terms of two modes as the basic variables to calculate the coupling behavior. As a criterion for determining the amplitudes of the two modes, the power transported on the two guides is used. An image guide coupler with a ferrite slab theoretically demonstrates the feasibility of this method. >

A general solution of the electrode resistance problem

Starting from the stationary current field problem of a three-axial ellipsoid, the solution of the electric potential is known. This solution and the results of earlier papers are used to calculate the electrode resistances. The main advantage of this method is that it contains the calculation steps not only for electrodes developed by three-axial ellipsoids but also for other electrode forms; e.g. spheres, rotational ellipsoids, etc. >

Non-uniform finlines on anisotropic substrates

Theoretical results for uniform finlines on anisotropic substrates are extended to tapered sections, paving the way for the design of optimal transitions to waveguides or other planar transmission media. A solution of the generalized telegraphists equation is described which takes into account the second-order effects such as dielectric and magnetic losses, finite metallization thickness, and substrate mounting grooves. Numerical and experimental data are presented and compared.<<ETX>>

Considerations on the frequency dependence of waveguide modes in premagnetized ferrites near resonance

The characteristics of the waveguide modes in premagnetized ferrites are described, taking into account the dielectric and magnetic losses. It is shown that the field distributions inside an anisotropic medium-filled rectangular waveguide can be calculated on the basis of a rigorous field theory. The authors then discuss how the field theory can be used for the design of high-quality isolators and phase shifters.<<ETX>>