A rubber coiled aerial (antenna) would be shorter than a solid one.
In essence the length of the aerial (antenna) is fixed by the frequency in use for the most efficient range.
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Seconded. The antenna length is determined by a fraction of the wavelength -- certain lengths enhance/reinforce certain frequencies, while cancelling/subtracting from others. To miniaturize you can often coil or fold the antenna.
I'm feeling really stupid right now. Antennae work by having the EM wave induce a current, hence the > 1/2-wavelength requirement. Since EM is (to zeroth order) transversely polarized, I don't see how a coiled up antenna could possibly work. Can you point me to a decent discussion of this (the Wikipedia article was a bit too basic, and stopped at the same dipole approximation I'm stuck on).
I don't know the specifics or the physics of it -- I just know certain lengths are required based on length. I know theres a 'diy high gain antenna' for wifi, and it involves both straight lengths, and coils to get extra-awesome signal amplification and attenuation (where needed)
. Check the ARRL web site. If you don't find what you need quickly, let me know and I'll investigate further. . IIRC, a coiled antenna uses its' own inductance as a loading coil, but it has been decades since I used that stuff.
Buy an iPhone?
But seriously, as has already been said, if you're designing an antenna for a cell phone, then investigate "fractal antenna design" using your favorite search engineyou can use "printed circuit" or "PCB" or "circuit board layout" as adjuncts for the search term for added "hit" content.