[penpen (OP)]

we are very familiar with the concept of a lens for visible light.
What would the analogue be for mobile frequencies?
as mobile frequencies are also a kind of radio signal,
what objects or material are designed to manipulate mobile frequencies the same way lenses manipulate light?

[RD]

... what objects or material are designed to manipulate mobile frequencies the same way lenses manipulate light?

Waveguides are to microwave radio frequencies what optical fibres are to light

Parabolic reflectors can be used to focus radio signals, e.g. satellite-TV dish.

[evan_au]

Any material which had a significant index of refraction at the frequency of interest, and had low attenuation at this frequencies could be formed into a lens which could focus this frequency.

This would have advantages for a "point-to-point" wireless link, where parabolic dishes are normally used today.

This would be less valuable for mobile handsets and mobile base stations, which must be able to transmit and receive in multiple directions, often at the same time. For this purpose, current systems typically use multiple transmitter and receiver antennas which each transmit a different version of the same signal, so that multiple paths between transmitter and receiver antennas allow greater bandwidth than a single transmitter and receiver antenna. This is termed a "Multiple-Input/Multiple Output" (MIMO) channel.

Even more interesting is the demonstration of "metamaterials" which can demonstrate a negative index of refraction at microwave frequencies, something that physicists and engineers would really like to accomplish at optical frequencies.

Note that the frequencies used for 2G, 3G and 4G cellular mobile systems are often driven by how much spectrum is available in a given country, at what frequencies, and how much the mobile operators want to pay for it.

[alancalverd]

Radiofrequency lenses are difficult to fabricate compared with optical lenses, but radiofrequency diffraction gratings are much easier - you can do it on a kitchen table with strips of aluminium cooking foil. A circular diffraction plate acts very much like a lens. 

[penpen (OP)]

for indoor lifting system, normally there is a penal antenna at the roof top, and a repeater up at the lift, so that to provide mobile coverage inside the lift.

however, can we remove the repeater, and replace by a lens(or other kind of materials ) to converge the radio frequency so that to provide mobile signal.

i am thinking that is it possible for all different frequencies 2G 1800Mhz , 3G 2100Mhz, 4G 2600Mhz to work? 
and what kind of material should be used.
and how about the size of the hole?
 could you give me some advice?

thank you so much!!!

[syhprum]

Fresnel type lenses consisting of metal plates that functioned as waveguides were used on some WWII radar systems, the problem with such antennas is the very narrow range of frequencies over which they function whereas a parabolic reflector is very achromatic

[penpen (OP)]

newbielink:http://www.adena.co.nz/theatre/tech-reference/how-things-work/luminaire-fresnel/fresnel-lens.gif [nonactive]

do you mean this kind of lens?
but what is the difference between this lens and normal Convex / concave lens?
could u give me some materials to let me know more about this.
thank you so much again.

[syhprum]

Sorry I can supply no further information as I was on relying on my recollections of a 1950 article in "electrical engineering" long since out of print

PS your link won't work for me "access denied"

[penpen (OP)]

sorry for the link,now is ok.
and how about the diameter of the lens?

[RD]

sorry for the link,now is ok.
and how about the diameter of the lens?

That's for light, the ones for radio-waves are metal rings, with non-metal gaps ..


http://isites.harvard.edu

BTW your idea of replacing the repeater on the elevator-compartment with a fresnel zone-plate lens is a non-starter :
a plain hole in the elevator-compartment of the same size as the lens would admit more radio energy than fresnel zone-plate, which reflects about half the energy hitting it , [although the half which passes through can be focussed down to a point].

https://www.google.com/search?q=fresnel+zone+plate+antenna+radio

[Bored chemist]

"Can lenses be built for mobile frequencies of 2G, 3G and 4G"
Yes