Right. There's some discussion of this in the ON4UN book, where I found
the Christman matching. As published there, it's 84 degrees of 50 ohm
line in each element, plus 71 degrees of 50 ohm line in the element
facing the desired forward direction,change directions by switching the
71 degree section.
--------------------
So the forward element is actually feed at 155 degrees?
Phase shift is NOT the length of a transmission line unless the line has 1:1
SWR, is lossless, and/or is a multiple of 90 degrees.
In a phased array, with equal 90 degree lines feeding each element, the
lines cancel out. Phase shift modification between elements caused by the
feedlines to the elements is zero.
In the Christman system, or any system where lines are not 90 degrees or
multiples of 90 and are also mismatched, the two 84-degree lines do not
quite cancel each other out. They reduce the effect of each other, but not
to zero like a 90 line or a matched line. They do add some phase shift, but
certainly nowhere near 84 degrees.
Also the 71 degree line, since it is not 90 and not matched, does not shift
phase 71 degrees.
Adding the line lengths together without considering impedance and
transmission line effects doesn't work. It is really a more complex answer
that requires looking at the system. Voltage and current are not even in
phase, so we also have to know if the element is driven by voltage, current,
or someplace between.
73 Tom
All good topband ops know how to put up a beverage at night.
_________________
Topband Reflector
|