W2RU - Bud Hippisley wrote:
> On Feb 11, 2009, at 12:54 AM, jimlux wrote:
>
>> I think if you're serious about phased arrays, then the few hundred
>> bucks for the VNA probably is the least of your problems.... in the
>> HF world, most users of arrays have large budgets...so they can
>> spend the time and
>> money on careful measurements of whatever is needed, including running
>> far field patterns using slick stuff like RELEDOP.
>
>
> So if the choice is one of buying either a VNA or an airplane capable
> of dragging a "sense" antenna around, you make the decision a lot
> easier for me, Jim....:-)
>
>
Laugh if you must, but I bought a 1/3 scale R/C powered parachute for
exactly this purpose.
http://www.luxfamily.com/jimlux/robot/ppc/firstflight.htm
The folks in the UK at DERA use a tethered blimp for this kind of
application. SRI uses a helicopter for RELEDOP.
The real challenge, by the way, is transmit, not receive. For receive,
you don't have to handle lots of power, so all digital approaches are a
fairly decent way to do the job AND there's huge literature on adaptive
algorithms to find and separate signals from an array. (e.g. ESPRIT and
MUSIC), so you don't really have to rely on a-priori steering of the
array. Heck, some are even available as canned toolboxes in Matlab.
(the fact that you can also turn the receive antennas into decoupled
voltage probes fairly easily also helps)
The problem is when you flip around to transmit. Knowing the receive
info doesn't necessarily give you enough to synthesize the transmit.
For one thing, the goals are different for receive (reduce the
interferers) and transmit (squirt as much power toward desired direction
as possible), and the issues with moving reactive power around the array
are a lot more important. (you could put all the elements far apart, so
there's no mutual coupling, but then you don't get any superdirectivity,
and I think you want superdirectivity in this application.. otherwise
you're limited to a gain of N)
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