- 作者: 陳俊雄
- 作者服務機構: Department of Electrical Engineering National Taiwan University
- 中文摘要: The spherical antenna which consists of a conducting sphere of radius a anda concentric spherical anisotropic surface of radius b(>a) is investigated both fromthe viewpoints of synthesis and analysis. First the principle in handling the polari-zation for electric fields is applied to the currents and is used as a basis forsynthesis of the antenna. The process aims at the goal of finding a linearly polarizedcurrent on the outer surface to produce a given field distribution. The variouscurrent distributions for producing the various wave modes are then discussed indetail. Next the antenna with a constant slope, conducting spiral over the outersurface is studied with uniform excitation across a gap at the inner sphere and atthe outer spiral. The results are presented and discussed according to the effect ofchanging the slope of the spiral upon the relative strength between TM and TEmodes. The important results are that:1) The antenna characteristics are mainlydetermined by the spiral current if the excitation is at the outer spiral, but by theaperture or leaky electric fields over the spiral surface if the antenna is excited atthe inner sphere. 2) The outer-excited spiral antenna would be uneffective for smallvalues of the spiral slope with reference to the equatorial plane, while the inner-excited one would not be effective for large values of the spiral slope.
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