Folded dipole
The standard story when talking about the folded half wave dipole is that it presents a driving point impedance of about 300 ohms resistive (4 times 75 ohms). We can easily measure this and the results of our measurements are presented here. In our exampl
In a single lambda/4 rod (one rod of the two forming the dipole) the current is maximum at the feed point, then decays co-sinusoidally to zero at the end.
In the case of the folded dipole, with a conductor bridge at the fold end, the two parallel conductors (closely spaced) form a parallel wire transmission line, of length lambda/4, and shorted at the fold. Thus at the other (feed) end, the parallel rod com
The differential mode current, as we have seen, is zero at the feed end, but a quarter wavelength away along the double rods it has risen to V/2Zo, where V/2 is half the antenna driving point voltage and Zo is the impedance, not of the radiating antenna,
The common-mode current which radiates is therefore twice the current delivered by the feeder to the real radiation impedance, and for the same total radiated power P = (IIR), the current I consists of two parts: I/2 from the feed and I/2 in the parallel
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