"Crazy George" wrote:
Well, let me just post this at the bottom. RCA made a line of
VHF TV transmitting antennas which were a slot arrays.
The only one I managed to get close to before it became airborne
and clamped a thousand or more feet in the air was for
channel 9. It was 80 feet long (2 - forty foot sections) and was
constructed exactly as Tom, K7ITM suggested, the phase
of the feed of each element was progressively changed,
in this case, to effect 1.50 of downtilt.
_______________

The antenna described above is the RCA "Traveling Wave" design. Without
beam tilt for the situation described, it has an omni, horizontal plane RMS
gain of ~17.2X (~12.4dBd) . The beam width within the 3dB points on its
elevation pattern is about 3.2 °.

If this antenna was placed with its radiation center 1,500 feet above smooth
earth, the radio horizon would be 0.59° below the horizontal plane, so using
beam tilt would raise field strength there. The 1.5° value stated above
exceeds that, but there may have been good reasons for it.

Adding beam tilt to an antenna with a very broad elevation pattern, and
installed on a short tower is a waste of time and money, however.

RF (RCA Broadcast Field Engineer, 1965-1980)

Visit http://rfry.org for FM transmission system papers.