Jim wrote:
I'll bet the hardware cost of a electronically steered phased array
for HF suitable for ham use is comparable to the hardware cost of a big
tower, rotator, and Yagi.. the phased array just isn't available as an
off the shelf product yet.


The fully steerable phased array that can also handle 1.5kW TX power is
not available as a HAM product off the shelf yet... but we can already
see where the future is headed.

Many people already have four-square phased arrays for the lower HF
bands, but we have hardly begun to tap their true potential.

The design company Plextek has a downloadable demonstration which shows
what a four-square phased array can really do:
http://download.plextek.co.uk/AKS06.zip

The user interface is a bit clunky, but stay with it...

The program starts with an omnidirectional pattern, receiving signal 1
coming from 90deg (blue arrow at 3 o'clock). The thermometer bar at the
top right is showing a positive signal/noise ratio (green).

Click in the 'Interferers' columns to bring up either one or two
interfering stations which are the yellow arrows. The thermometer bar
now shows a negative s/n ratio on the wanted signal (red).

Now the fun starts: in the 'Algorithm' column, click on 'SMART' to turn
on Plextek's proprietary adaptive array software - watch the phased
array reconfigure itself automatically. The pattern adapts to null out
*both* of the interfering signals, while still keeping a lobe pointing
towards the wanted signal. The wanted signal reappears from under the
QRM and its s/n ratio increases dramatically.

You can then drag the interfering signals to different directions, and
the array keeps on adapting. The only case where it can't give any
improvement is where the interfering signal comes from exactly the same
direction as the wanted signal.

All this is done by varying the amplitude and phasing of the signals
from each of the elements before combining them. The 'WEIGHTS' table at
centre right shows what is required. On transmit, the same directional
patterns could be achieved by applying the same weightings to the
currents that are fed to the four elements - or of course you could
switch to a different pattern while transmitting.

OK, this is only a demonstration. It doesn't consider signals at a range
of different vertical angles; it doesn't consider the big practical
problems of achieving the correct current weightings when all four
elements are interacting; and it doesn't consider how to handle the TX
power. Even so, it will open your eyes to what a phased array can really
do.

It's all down to the magic phasing box at the centre of the array.
Whatever goes into that box will be hard to design, complicated to
control, and expensive to build... but most four-square owners would be
happy to have even a fraction of those extra capabilities.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek