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

>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

Hello, and at risk of stating the obvious the calculation of driving
point impedance does not make any sense when multiple sources are
simultaneously present, be it a multiple-source fed antenna/array or
an electrical network circuit. A V/I calculation at a feedpoint is
NOT the driving point impedance under such conditions. IOW, if
components of the voltage or current are present that did not emanate
from the driving source under cansideration, they cannot be part of a
driving point impedance calculation.

The calculation is performed with the remaining sources
short-circuited (voltage) or open-circuited (current). In either
case this places the imittances asscociated with these remaing
sources across their respective feed terminals to the antenna/array.
Circuit Theory 101. Sincerely,

John Wood

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