In a similar way, if this antenna is made of dielectric material, then the radio-frequency electromagnetic waves are collimated in a similar way and are transmitted further.
In this way, the signal from a lens antenna using a feed element is transmitted. Hence, the parallel rays are obtained at the right-hand side of the optical lens. Thus, after incidence when the rays pass through it then the diverging rays collimate due to refraction and is converted into plane wavefronts. So, when the feed antenna (generally horn or dipole antenna) is present at the focal point (present on the left-hand side) of the lens then the spherical wavefront emerging from the source which is diverging in nature incident in the surface of lens antenna.
We all must be aware that from the optical point of view, light when falls on the surface of the lens then it bends due to refraction and the way of bending of light energy depends on the curvature as well as material from which the lens is made.
But these can also be constructed with materials that exhibit less than unity refractive index at radio frequencies. It is noteworthy here that in general practice the collimating lens is made of dielectric material which possesses the finite value of dielectric constant. This optical surface forces the radiated spherical wavefronts to get changed into collimated one. In a similar way in case of lens antenna, the point source acts as the feed that emits the microwave energy towards the surface of the optical lens. We have seen in a parabolic reflector that the energy emitted from the feed element which is present at the focus of the reflector when reaches its surface then it converts the spherically radiated microwaves into plane waves. We are familiar with how a simple optical lens performs collimating action. Lens antennas use the principle of the converging lens in order to collimate the energy that incident on it. This prevents the undesired spreading of the energy thereby improving the efficiency. Similar to a parabolic reflector, a lens antenna is designed to collimate the incident energy which is diverging in nature, in the desired direction. This causes an increase in the directive gain offered by the antenna arrangement. Thus, results in converting the spherical waves into plane waves. In the previous article, we have discussed the reflector antenna that allows the energy falling on its surface to collimate in the desired direction. Its operation is similar to reflector antennas. Lens antenna is regarded as a radiator which operates on collimated action of optical lens. This is the reason these are suitable for very high-frequency operations. It is to be noted here that in case of low-frequency operations, the dimensions become very large thus antenna arrangement becomes bulky.
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