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

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.)

The best simple description of what to do with negative elements in a phased
array is in Whit Griffith's "Radio-Electronic Transmission Fundamentals"
Chapter 51, p. 432. This chapter gives a straightforward explanation of how
a multiply-driven phased array works. Negative resistance has nothing to do
with any complex energy storage or such, it's just the result of mutual
impedances, and the negative element is a receiving antenna.

Ben Dawson
Benj. F. Dawson III, P.E.
Hatfield & Dawson Consulting Engineers, LLC
9500 Greenwood Ave. N.
Seattle, WA 98103 USA

"James P Lux" <James.P.Lux_at_jpl.nasa.gov> writes:
> John Belrose <john.belrose_at_crc.ca> writes:
> >
> > Jim, negative input impedances frequently occur in phased array
> > (MF
> > broadcast) antenna systems. Another example is given in my
> > chapter
> > on VLF, LF and MF Antennas [1], pp. 614-615. This is because you
> > are
> > using multiple fed the antenna system. --- two or more sources.
> <snip>
> > John S. (Jack) Belrose
> >
>
> And, presumably in such cases, one can't use a separate power
> amplifier for each element, since, by and large, amplifiers
> won't work to turn RF power back into DC bus power. It's an
> interesting idea.. it's used in power engineering - 4 quadrant
> motor controllers do it, for instance.
>
> Perhaps, if one has a system with nonreciprocal devices in the
> feeds (i.e. a power amp on each element), that implies some
> constraints on the types of beams that one can form.
>
> Jim Lux
>
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