But a wide spaced line WILL radiate. Antennas are made of slightly wider
spaced parallel lines, for example the Quad, where the spacing is
quarter wave. The connectors top and bottom (if horizontally polarized)
radiate perpendicular to the plane of the element, while there is a
cross polarized lobe at about 45 degrees from the horizontal radiation
lobe. That's because while the vertical conductors are OUT of phase when
viewed from a position perpendicular to the plane of the wires, and so
the field in that direction cancels, but then viewed from within that
plane (e.g. parallel to the spacers), the radiation from those currents
are NOT completely out of phase. They are not out of phase precisely by
the phase angle of the distance between them. For the quad thats 90
degrees. That's presuming that the energy is carried ONLY in the
currents, that there are no accompanying fields.
But I have some experimental evidence that much of the energy of a
balanced line is carried in fields surrounding the line. Then changes in
direction of the line tends separate field from the line (much as a
G-line) as do intrusions into that field. I don't have measurements of
that dimensions of that field. But here's how I noticed it. I was
checking line loss by shorting lines and noticing the difference between
forward and reflected power at 144 MHz. First I checked a length of
RG-58 and the loss indicated was exactly the value listed in the tables
of cable loss. Then I added a coaxial half wave balun and the loss
increased. Then I added a length of K-200 heavy duty balanced line. It
has a pair of 12 gauge or 14 gauge conductors spaced about 3/4" in an
oval of polythylene. I shorted the end opposite the balun by folding the
conductors together and soldering them. I suspended the line clear of
metal objects. The SWR went way down indicating considerable line loss.
Then I moved a large sheet of copper up against the short, and the loss
went down to what I expected. That tells me that much of the energy is
carried in the field surrounding the balanced line and interruptions in
the line diretion will separate the line from the fields. That's
radiation.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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