"Robert Lacoste" wrote in message
...
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

No point using a "short" aerial as the radiaton angle will be up in the sky
and coverage absolutely rubbish.
The easiest aerial you can make is from a piece of 300ohm ribbon cable.
It's a slim jim type aerial which has a low angle of radiation and will give
a brilliant coverage compared to expensive colinear aerials.
You can just roll it up and stick it in your pocket, then when you want
to use it - hang it from a curtain rail. or a tall structure. No need for
any
ground.