On 7/19/2011 8:08 PM, Richard Clark wrote:

If you had two verticals spaced some distance apart, fed by equal length
transmission lines, and one is polarity reversed, you get a fairly sharp
null on the line perpendicular to the line between the antennas.
(e.g. a signal coming from broadside will exactly cancel in the combining)

Hence my referenced Cardiod antenna available for modeling with EZNEC.

Cardioid has only a single null and is a "end fire" configuration. I
don't think (esp with short spacing) you can get as deep or narrow a
null as with a W8JK style antenna(short spacing, out of phase).

two 180 degree out of phase antennas can be very narrow, even with small
physical extent.



A loopstick antenna on a ferrite core or a multiturn loop, as popular in
direction finding, is another example with a fairly sharp null.

Mike has explicitly rejected loop solutions.

Perhaps big loops were rejected.. what about physically small loops.


Now.. if you want one null, and one null only, that gets a bit trickier
in a small space. I don't know that you can do it with only two
elements (haven't thought about it much).

And if you want to steer the null.