Topband: "Phased Verticals with Continuous Phase Control"

[Tom Rauch]

> One thing that seems a little glossed over is that the
> phase shift network is designed for 52 ohm inputs and
> outputs, with antennas that are 'roughly equivalent
> impedance'. Sounds like keywords for 'in theory', but
> would appreciate anyone's comments, especially those
> with practical experience with this.

We have to be careful with what we read in articles that are
not technically reviewed.

Phased antennas that are fed exactly in-phase or
out-of-phase (zero or 180 degree) no longer have the
impedance they have when used alone. The only exception is
when very high losses swamp out mutual coupling effects.

If he designed a phase system for 52 ohms with a
unidirectional phased array the real world results will be
nothing like predicted assuming 52 ohm loads.

Worse yet in a two element array series fed elements fed at
the current maximum require equal feed currents at the
antenna. This is far from equal power! When voltage fed the
elements require equal feed voltages. When something between
or gamma matched the result is something between those two
extremes.

The only time a transmission line has a delay equal to its
electrical length is either when the line is any multiple of
1/4 wl, or when the line has unity SWR. Phase error caused
by line mismatch peaks at odd multiples of 1/8th wave, so a
3/8th wave line would have maximum phase error.


We can plan a system to work when the delay lines and feed
lines seem to break the rules. That system may work, but if
the article says what you repeated...the author doesn't
understand what he really did. At times we might make
combinations of errors and dumb luck might just happen to
cancel out errors.

73 Tom