Preliminaq results are reported on the design of a tunable magnetron for operating frequencies up to 140 GHz. The experimental device has a mechanical tuning tuning range of 1.5 GHz and a good spectrum. The power output variation is within *20% over the tuning range. 0 1996 ABSTRACT Three closed-form expressions are presented for the calculation of resonant frequencies of rectangular microsmp antenna elements. They are derived by modifiring the transmission-line model and the cavity model, and by the curve-fitting method. The results of these expressions are compared with the measured resonant frequencies of antenna elements with substrates that satisfy the thickness criterion h 2 0.0815h0, where A, is the free-space wavelength and h is the thickness of the substrate. Calculated results are in excellent agreement with measurements. 0 1996 John Wiley & Sons, Inc.
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