Topband: superdirectivity

[Sam Dellit]

g'day to all on the topband reflector

the topic of supergain and superdirectivity was at the cutting edge of
antenna technology in the 40s and 50s. ultimately it was determined
experimentally that once more than a very few extra dB of gain was achieved
that high mutual impedances resulted in one or more elements having very low
radiation resistance, leading to high power losses and negating any other
achieveable gain increase. similarly considerable pattern instability
resulted, so that minor changes in antenna parameters led to very large
terminal impedance variation and pattern variation. the conclusion was also
subsequently proven theoretically.

i understand the problem (well a little anyway) for transmitting antennas
which need to be resonant for reasonably high efficiency. resonant antennas
need to be very widely spaced if mutual impedances are to be kept low. but i
wonder whether a closer approximation (to superdirectivity, not supergain)is
achievable with receive only antennas. short non-resonant antennas are
entirely acceptable for receiving purposes and have much lower mutual
impedances

anyone have any thoughts, or previously looked at this?

73s gd dx de

sam dellit vk4zss


--
FAQ on WWW:               http://www.contesting.com/FAQ/topband
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com