| 摘要 |
A non-resonant antenna structure for the reception and/or radiation of electromagnetic waves in a unidirectional manner over a broad frequency band. The structure consists of two resonant elements of dual type fed simultaneously from the same transmission line. The resonant elements are adjusted so that the image impedance of the composite two-port structure is nearly constant and resistive over a very wide frequency band. One port is terminated in a resistor approximately equal in value to the image impedance. As a result, the impedance observed at the other port is also very nearly a constant resistance. In a given plane through the antenna one element has an omnidirectional radiation pattern; the other, a typical figure-of-eight dipole pattern. Proper adjustment of feeder impedance relative to the impedances of the individual elements leads to a unidirectional pattern with high front-to-back ratio over the operating band. Since achievement of the above conditions is possible at frequencies below the first resonant frequency of either element, the antenna dimensions may be small compared to the wavelength, particularly at the lower end of the operating band.
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