Engineering topics
Publications and source records attributed to Kosmahl, H..
The application of the TWT - the backbone of all civilian and military space communication programs - to past, present and future satellites is discussed. Performance characteristics and the trends and challenges in the future are reviewed. Finally, a comparison with Solid States devices, as derived from fundamental laws, is made and limitations discussed.
Measurements, at low frequencies, of the shot noise current from space charge limited cathodes always produced results substantially in excess of theoretical predictions. Measuring the ratio (I sub eq)/S yielded a relation (I sub eq)/S = 1.288 V sub k = 1.288 k(T sub k)/e, independent of the operating point of the diode (triode) as long as all parts of the cathode had a full space charge controlled emission. This method was so sensitive as to permit detection of cathode temperature changes by 1 K, thus it allowed a powerful screening method between well and poorly activated cathodes, superior to dip tests and other current-voltage methods.
The design and development of a 200-watt-output, traveling-wave tube (TWT) for the Communications Technology Satellite (CTS) is discussed, with emphasis on the design evolution during the manufacturing phase of the development program. Possible further improvements to the tube design are identified.
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Improvements were carried out on a TWT (traveling wave tube) for use in EMC (electronic countermeasure) systems by applying MDC (multi-stage depressed collector) and spent-beam refocusing techniques. The MDC geometric design consists of six collecting elements (electrodes) at ground and cathode potentials operating in 2 or 4 stage configuration. The refocusing system designed allows a controlled beam expansion to the point that space charge becomes negligible at the MDC entrance. Simultaneously, the standard deviation of the radial velocity (angular spread) is reduced. This system provides an analog real time readout of P(recovered). Data on all tests is obtained with an automated data acquisition system.
Feasibility evaluations of klystron amplifiers for conversion of solar power in synchronous orbit into microwave power at 2.4 GHz and transmission to earth were carried out. It was found that amplitrons and klystrons, using a depressed collector augmentation, can achieve efficiencies in excess of 80% if the power output is kept higher than 50 kW. Body wound selenoid provides the needed beam-focusing field. Narrow bandwidth requirements permit a low cathode loading density of 0.5 A/sq cm produced at approximately 850 centigrades. Emission tests indicate a potential life expectancy of 20 to 40 years.
Design and performance of a small size, 4-stage depressed collector are discussed. The collector and a spent beam refocusing section preceding it are intended for efficiency enhancement of octave bandwidth, high CW power traveling wave tubes for use in ECM.
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