Klaus Schunemann

Complex and Backward-Wave Modes in Inhomogeneously and Anisotropically Filled Waveguides

A rigorous analysis of lossless inhomogeneously and anisotropically filled waveguides of arbitrarily shaped cross section is presented. The mode propagation constants squared appear as eigenvalues of a real infinite-dimensional characteristic matrix, which is, in the general case, nonsymmetric. Complex conjugate pairs of eigenvalues are then possible, which give rise to complex modes. Modes at cutoff are shown to be either TE or TM with real cutoff frequencies. An investigation of the power flow shows that backward-wave modes may exist as well. Different orthogonality relations are derived from which the power coupling between complex modes is investigated.

The Effect of Complex Modes at Finline Discontinuities

The effect of ignoring complex modes on the solution of finline discontinuity problems is investigated. It is shown that the modal energy distribution at both sides of the discontinuity may be greatly affected by overlooking complex modes, even if they are not strongly excited. lt is also shown that disregarding only one mode of a pair of complex modes, while taking the other into account, results in a contradiction to the principle of complex power continuity across the discontinuity plane. Comparison to measured data is also given to justify the validity of the numerical results.

Application of the generalized spectral-domain technique to the analysis of rectangular waveguides with rectangular and circular metal inserts

The generalized spectral-domain (GSD) technique, which was previously developed and tested for some special cases by the authors (see ibid., vol.37, p.1924-32, 1989), is applied to the analysis of rectangular waveguides with rectangular and circular metal inserts. These include conventional ridge waveguides, circular-ridge waveguides, and rectangular coaxial lines, with either rectangular or circular inner conductors. The numerical results show that a previously published description of the edge behavior of the electromagnetic field is incomplete. A constant term must be added to the expansion of the magnetic field component which is parallel to the edge. Excellent agreement with other published analysis data is achieved, with a drastic reduction of CPU time for the conventional ridge waveguide. The accuracy of the results is demonstrated by two- and three-dimensional plots of the field distributions. >

Self-consistent simulation of the spatial-harmonic magnetron with cold secondary-emission cathode

A self-consistent mathematical model of the spatial-harmonic magnetron (SHM), with cold secondary-emission cathode is proposed for investigating steady-state processes. Characteristic features of modeling space charge effects, secondary emission, and nonlinear electron-wave interaction are described. Illustrative examples of simulations are given in order to show peculiarities of the operation of the SHM as compared to conventional magnetrons. Multi-stable states of the magnetron are described. Results of simulations are compared with experimental data for an 8-mm-wave magnetron.

Analysis of Fin-Line Discontinuities

Various discontinuities in the slot width of fin-lines are accurately analysed. These include a step in the slot width, an inductive notch, a small capacitive strip, and a longitudinal stripe for mounting a semiconductor diode. Equivalent circuits are derived and related to the geometrical parameters. The results can directly be applied to a design of impedance transforming and filter networks.

Design and Performance of Fin-Line Bandpass Filters

A transmission resonator implemented in fin-line technique is rigorously analysed by applying the method of equivalent rectangular waveguides. Based on these results, bandpass filters with up to 5 resonators are designed taking the higher-order mode coupling between the resonators into account. It is shown that this effect is of considerable importance in the design of fin-line bandpass filters.

Impact-ionization effects on the high-frequency behavior of HFETs

A new small-signal equivalent-circuit model is presented, which takes into account strong impact-ionization effects on the high-frequency behavior of heterostructure field-effect transistors (HFET). The proposed model overcomes the limitations of previous models and includes the bipolar action of the space charge of holes generated by impact ionization. It is shown that the developed model is capable of explaining the anomalous high-frequency behavior of HFETs with channels of high indium content.

A Quadriphase Fin-Line Modulator

A hybrid-coupled quadriphase rnodulator which has been realized in fin-line technique is described. It operates over a 15-percent frequency band around 15 GHz with an insertion loss of 1.7 dB. The circuit has been scaled to twice the operating frequency. The insertion loss then amounts to 2.2 dB. Furthermore, it is shown experimentally that the performance of the modulator does not degrade if the dimensions of the waveguide housing are altered to amounts of up to 10 percent.

Analysis of waveguides with metal inserts

A systematic analysis of waveguides with metal inserts is presented. The method is based on a field expansion in terms of the normal modes of the corresponding hollow waveguide without metal inserts. The analysis leads to two formulations: a matrix formulation and a moment-method formulation. The matrix formulation is suitable for structures with smooth metal inserts which are free from sharp edges, while the moment method is more suitable for metal sheets (e.g. strips and fins) or metal inserts with sharp edges (e.g. ridges). The validity of the method is tested by investigating some special cases in which the surface of the metal insert coincides with one of the coordinate surfaces, e.g. a bifurcation in circular or rectangular waveguides. The method is then applied to the analysis of striplines and ridge waveguides. It leads to a generalization of the widely used spectral-domain technique in that ridges, fins, and strips with finite thickness can now be analyzed likewise. Any existing routine for the analysis of planar structures which is based on the spectral-domain technique can then be slightly modified in order to take the metallization thickness into account. >

Millimeter Wave Transmitters on the Basis of Spatial-Harmonic Magnetrons with Cold Secondary-Emission Cathode for Coherent Radar Systems

Spatial-harmonic magnetrons with cold secondary-emission cathode are promising oscillators for various millimeter wave radar systems. Experience in the development and application of transmitters on the basis of such magnetrons for coherent radar systems is summarized. Design approaches to the development of highly efficient transmitters for the frequencies of 36 GHz and 95 GHz with the power level of 30 kW and 4 kW, respectively, are discussed. Cloud Doppler radar systems based on such transmitters are described as examples of the transmitter applications.