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Dielectric-coated hemispherical dielectric resonator (DR) antennas fed by a microship line through a coupling slot are analyzed, The broadside TE,,, mode is studied, and the reciprocity theorem is applied in this analysis. In this case the dielectric-couted DR antennu can be uiewed as a series load at the slot position as seen by the microstrip line. The impedunce of this series load is calculated by using a Green's,function formulation, and the input impedance of the slot-coupled DR antenna can then be obtained using transmission-line theory. Numerical results for the input impedance ure calculated and presented, and the antenna bandwidth is discussed. It is observed that the antenna bandwidth of u dielectric-coated DR antenna can be as high us two times that of a D R antenna without a coating. 0 I995 John Wiley & Sons, Inc. 355-357. 1165-1167.Received 7-7-94; revised 8-26-94 Microwave and Optical Technology Letters, 8/1, 13-16 0 1995 John Wiley & Sons, Inc. CCC 0895-2477/95 ABSTRACT W -band dual-frequency circulators have been dmeloped. The dualfrequency circulator resulting from a dual higher-order mode i s used as stated in 13, 41. f i e calculated properties of the dual modes, especially the mode-change jkquency point between the dual higher-order modes, have been venjied experimentaliy. 8 1995 John wiley & Sons, Inc.

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