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Yagi Antenna Question
I disagree unless yoiu are specipically adressing the yagi design
which is an explanation in terms of vectors.However an element radiates a field not a vector. To 'maximise' the redirection of rear field generation requires multi "reflectors" or a dish to capture all the rear radiation. Tho a dish is used for micro wave frequencies it can be simulated by multi reflectors aranged in parabolic form. This method is not as mechanically feasable as the Yagi but does illustrate the effectiveness of a "refletor" versus a "director" in terms of "efficiency" or "effectivenes" ala, the two element yagi..when viewed as a mesh cuircuit assembly. and reradiator ((reflector) longer physical length is not a necessity.as implicated by the Yagi inline design. Art wrote: chris wrote: Why (or how) does the longer element "reflect" the radio wave, A reflector does not reflect anything. It reradiates. When a element is self-resonant it reradiates with 180 degree phase inversion. Spacing from the driven element causes a phase delay. Lets say that spacing is 90 degrees. so, on many multi-element Yagi designs, the norm seems to be just one reflector, and many director elements. Does this mean that the reflector is more "effective" than the directors at modifying the radiation field? No. Once something removes energy form the rear, there is no more energy to excite and further elements. You can't excite additional reflectors because there is no energy there to excite them, and so they become useless hunks of metal without much current. 73 Tom |
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