There are a couple of distinct advantages of the W8JK over the antennas
I described. One is that it can be fed with two equal lengths of
transmission line to the elements, one being given a physical half twist
to effect the phase reversal. Then you have an antenna whose properties
remain the same over an extremely wide bandwidth. The second is that the
free-space pattern consists of two relatively narrow lobes in the
vertical plane, with an overhead null. This results in a concentration
of radiation at lower angles than you'll get with a typical Yagi or most
other two element horizontal antennas.

The tradeoffs are that because of the bidirectional pattern, half the
radiation doesn't do you any good; there's no front-back ratio (although
it's also poor on the maximum-gain antennas I described); and loss has
to be managed and can potentially be a problem because of the low
feedpoint impedances.

There's no single perfect antenna -- you pays your money and you makes
your choice. As Richard Heinlein so succinctly said, TANSTAAFL.

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"The W8JK doesn`t provide thye most gain of any two element array of
half wavelength elements for a given spacing."

The W8JK had the highest gain of the 5 examples compared in the table.

The advantage of EZNEC is shown in Roy`s posting.

Roy also wrote:
"At 0.25 wavelength spacing, 142 degree phasing gives the highest gain,
just over 1 dB greater than a W8JK. These phasings also provide a higher
nfeedpoint impedance than a W8JK,---."

I`d rather have Roy`s antenna.

Best regards, Richard Harrison, KB5WZI