I'm looking for an isotropic antenna for the frequency range 10 MHz to 3 GHz that detects fields independent of direction and polarization.
I found only this brand:
(Quasi isotropic ultra broadband antenna UBB27-SA3) from gigahertz-solutions Germany. Does any one know any other affordable alternatives ?
10 MHz to 3GHz bandwidth is possible with ultra-wideband (UWB) monopoles. But non of the antennas are isotropic, they can be omnidirectional-Quasi isotropic (at maximum). Now for polarization independence, Dual polarized UWB antenna can be used.
Since the bandwidth is very high from 10MHz to 3GHz, non-uniform Helical antenna may be used to generate quasi-isotropic radiation pattern.
Cheapest antenna for such wide band width could be Helical antenna with fixed Apex angle (outwardly increasing diameter) or you may try for spiral. Chances of getting commercially available at low cost is very remote, probably not possible.
For a direct answer, there is no such thing as an isotropic antenna as you request. There is always a pattern and polarization. In a statistical sense you can approach such (Dyson did that 50 years ago with conical log spirals on all 6 faces of a cube and fed by noise). Omni antennas are possible with a very wide bandwidth, but commercial systems are a different issue. Good luck.
W.A. Davis, I think the 3-axis probe exists for example this one, the manufacturer mentioned in the first page that "The isotropic antenna
detects fields independent of their direction and polarization. "
http://www.rohde-schwarz-ad.com/docs/emc/TS-EMF_dat_en.pdf
Note that the probe from rohde-schwarz is called isotropic, but is actually 3 orthogonal elements that are switched. Some of the PR in the PDF is a bit misleading as with the figure that says 3 isotropic elements. However, in the spec sheet it says the isotropic nature is obtained by switching 3 orthogonal elements. Getting full coverage, independent coverage of polarization is still a challenge, but there is not a single antenna element that is giving the isotropic performance. The latter is physically impossible. The switching is similar to the noise approach I mentioned of Dyson.
OK, Thank you Prof. Dr. W.A. Davis for your useful information
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