On Dec 18, 8:05*am, "Robert Lacoste"
wrote:
Dear all,

For a quite specific application I'm looking for an antenna design with
ideally the following characteristics, which are, I know, contradictory :

- 2m band
- TX (low power, less than 1W) & RX
- ultra compact, ideally able to fit in a 12-15cm x 5 cm x 5cm volume
- as omnidirectionnal as possible on the horizontal plane
- more or less vertical polarisation
- raisonnable gain for its size (-5 to 0 dBi ?)
- low dependency to nearby grounds (would be installed either at ground
level or on a wall)
- could be narrow band (say 1MHz) but in that case with stable tuning...
- low cost

Not trivial, isn't it ? For the moment my best match is a dual helix antenna
(two colinear helix, each made with a L/4 long wire, driven differentially),
but performances and size are not optimal.

Any good idea ? Would small magnetic loops be usable in such high
frequencies and small size ? Has someone already experimented other good
designs ?

Thanks,
73s,
Robert

a rubber duck or just a loaded vertical should do it. add a small
ground plane or counterpoise coiled in the allotted space and you may
even get better than 0dbi.