K. Schunemann

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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(More)
Ohmic losses in coaxial gyrotron cavities with corrugated insert are calculated on the basis of the rigorous singular integral equation (SIE) approach. It is found that SIE predicts significantly lower losses in the corrugated insert compared with the surface impedance model (SIM) widely used before. Calculations are performed in a wide range of corrugation(More)
A quasi-optical power combiner for a five-element in-line oscillator array is experimentally investigated at 150 GHz. The combiner consists of a periodic dielectric phase grating (hologram) which transforms the near-field of a rectangular horn antenna array into a pseudo-plane wave. The horn array is excited by IMPATT oscillators operating uniformly in both(More)
The development of a 210-GHz spatial-harmonic magnetron with a cold secondary-emission cathode is presented. The development includes a detailed self-consistent tube simulation and optimization. Based on these results, 210-GHz tubes providing over 1-kW peak power were produced and tested. Experimental results are consistent with the simulation.
A 16-vane millimeter-wave spatial-harmonic magnetron (SHM) with a cold secondary emission cathode is examined by the use of a 3-D particle-in-cell (PIC) code embedded in CST Particle Studio. Simulations of the SHM are performed without artificial RF priming and without assuming restrictive assumptions on the mode of operation or on the number of harmonics(More)
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(More)
Maxwell's equations for longitudinally inhomogeneous (irregular) waveguides with impedance walls are equivalently reduced to an infinite set of ordinary differential equations (ODE) by applying transverse expansions. The resulting set of ODE is used for analysis of gyrotron cavities. In particular, the effects of mode conversion and ohmic losses on the(More)
The design of a subharmonically pumped mixer in the submillimeter wave range is discussed, in which several single diode mixers are used. An important design criterion is the separate biasing of each single diode mixer. A distribution structure for the RF signal is given that avoids power splitting. The feeding network of the LO frequency was assembled at(More)
The well-known coupled mode theory is extended to the case of irregular waveguides with impedance boundary conditions on the walls. The developed theory is tested by calculating mode conversion and quality factors of a typical THz gyrotron cavity. High computational capabilities of the approach developed are found and a good agreement with earlier results(More)