antenna for a non-air medium, a higher permitivity medium
I have been trying to understand the effect on microstrip antennas design dimension if placed in a background environment of permittivity er, other than air = 1.
please suggest me any paper over this or it would great help if one can write about their opinion about it.
under a higher permittivity environment size of the antenna may became small but need to understand the relation between antenna dimension and the environment permittivity....
radiation characteristics will also get affected in such environment... i am looking towards understanding such effects
with regard,
lkminz
There are many papers and books on this theme, mainly focused on antennas for medical application, plasma research, etc.
If a wave propagates in a higher-permittivity medium than in a vacuum, its length becomes the original divided by a square root of the real part of medium permittivity. Similarly if an antenna is buried in such medium, its dimensions should be related to the actual wavelength in the medium to obtain the radiation pattern "scaled" from the air or vacuum we are used to.
Funny you say that. I've been thinking about making an antenna for one of the HF amateur bands by putting it in water. The relative permittivity of water is 81, so length of elements reduce by a factor of sqrt(81)=9. However, I'm not sure if the conductivity of pure water will kill this idea or not. I know someone done a quick calculation of the volume of water needed for a top band (160 m) antenna and it was several hundred tonnes assuming you keep lambda/4 of water around the antenna. Clearly a small volume on the outside of a dipole wont have a significant effect. But I think a vertical for 20 m band (normally 5 m high) could be put in a water butt. The 40 m ham band might just be doable, though I don't think there will be enough water around the antenna to get the full nine times reduction in length.
Of course, using a low loss material with a high dielectric constant would be best, but I'm not aware of any liquid which is cheap and good.
This is the sort of thing you could play with in an EM simulator. I'd start looking at things like dipoles and monopoles first, before worrying about more complex antennas.
I like the idea of immersing your HF antenna in water! You will have to used a distilled and deionized water I think but the other problem is how to facilitate the transfer of your HF wave through the water/air boundary, to make it propagating farther. My friend OK2ER of BTV company "www.btv.cz" has improved a MLA loop antenna to cover the amateur bands from 3.5 to 28 MHz in one device, and he claims that it works fine while the size is ~ 70 cm diameter loop. Contact him and save water!
A patch antenna surrounded with a high-k dielectric will radiate the same way like in air or vacuum if its size is scaled by 1 / (sqrt k); the other problem is that the wave generated or received by it must then leave the bulk dielectric and propagate out of it, in ait or vacuum. The air/dielectric boundary will reflect most of its energy back. A good transition can be made as a taper several wavelengths long but it will be quite huge. This is why I started my comments by mentioning medical applications of such antennas which operate in a contact with a tissue. The tissue is the dielectric (quite inhomogeneous) and such antennas are named applicators as they must be in contact with the tissue surface. Still the boundary is a problem, sometimes eased by the distilled deionized water or a dielectric alumina powder filling in the applicator antenna.