Topband: My Turn For a Brain Pick - Sanity Check

[Tom W8JI]

> 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