Re: NEC-LIST: Negative driving point impedances in phased arrays

"Ben Dawson" <dawson_at_hatdaw.com> writes:
> It is perfectly possible to use separate amplifiers for each element which
> requires positive power flow, and dissipating resistive loads for the ones
> which have negative power flow. In fact we just designed a system for an
MF
> array in which 15% of the power is consumed in the negative tower load.
The
> stability and bandwidth are better than for the case where the negative
> power is put back into the system bus by a "re-entrant" circuit. (Similar
> to putting the termination load power back into the system in a Rhombic
> antenna. Negative elements have modest power flow in typical systems.)

It would seem, though, that if you are operating in an environment where you
are transmitter power limited (either by power available, or by regulatory
fiat), one might want to avoid dissipating some of that power in a load. I
suppose, in the regulatory case, it depends on where the "measurement plane"
is for transmitter power. That is, if you dissipate power in a load
internal to the physical transmitter (say, in a pad used for power trimming)
is that any different than dissipating power in a load external to the
transmitter.

This brings up an interesting optimization constraint for a phased array.
If the goal is to maximize the radiated power in a given direction, AND
you're using an array of amplifiers, the optimum phasing might not be the
one that would produce the highest "antenna gain" (as if you had a single
feed). You'd want to maximize the power from each amplifier.

Thanks to all for all the useful discussion.. even if we have strayed
somewhat from NEC related issues....

Jim Lux

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