PROPOSAL FOR A TWO ELEMENT BEAM USING COMPRESSED DIPOLE LOOP ELEMENTS FEB. 15, 2000
These are the dimensions for the beam for the 20 metre band.
Note that the elements are not tapered because when I attempted to use that feature, I exceeded the number of wires allowed by the software. The wire is #14 AWG.
This is what the beam looks like:
Note that the feed point is the dot where the upper arm of the driven element crosses the Z axis.
Next I will show the 2D pattern.
Note that the F/B ratio is more than 20 dB. There is a secondary upward lobe that is about 17 dB below the main lobe. This can be made smaller by reducing the height of the antenna but the F/B ratio will suffer. Also, the takeoff angle will rise. The impedance can be reduced by shortening the elements in the y axis and making them larger in the Z axis.
Two hundred and eighty eight pulses were used to analyze the antenna. This is close to the maximum that NEC4WIN can handle. If you use more pulses with NEC2D, you will find that the resonant frequency will drop. Expect actual elements to be about 5 % smaller than given here for the same frequency. The reflector is only slightly longer than the driven element. This is because the bandwidth of the elements used is considerably smaller than full size dipole elements.
Next, I will show the 3D far field pattern:
Please note that NEC4WIN is no longer available. You will have to use another simulation program. As you can see, this beam offers good performance with only two small elements. Please note that I have not built this beam so if you try it, expect to spend considerable time and effort optimizing it. Good luck. Please let me know how it turned out.
My email address is [email protected]
This page was last updated Sept. 12, 2015.