Lens Antenna

They are usually made of polystyrene or Lucite. They are used to:

Control the aperture illumination.

Collimate the electromagnetic rays.

Produce directional characteristics.

Converge the incoming wavefront at its focus.

Produce plane wavefront from the spherical wavefront.

Salient features of dielectric lens antenna

They are usually made of polystyrene or lucite and polyethylene. Dielectric constant of polystyrene ∈r = 2.56, refractive index, n = 1.6 For polyethylene, ∈r = 2.25, n = 1.5.

They are bulky and heavy for f < 3 GHz.

Uniform illumination for lens antennas is better if the focal length is long.

At f < 10 GHz the lens become excessively and undesirably thick.

The main disadvantage of the dielectric lens is its frequency sensitivity.

The un-stepped dielectric lens is wide-band and its shape does not depend on wavelength.

The main advantage of lens antennas is that the feed antennas do not obstruct the aperture.

Tolerance in the design of this antenna is more.

Feeding at a point away from the axis is possible and it is suitable to move the beam angularly with respect to its axis if required.

Lens antennas are costlier for similar gain and bandwidth in comparison with reflector antennas.

They are also bulky and heavy. Designing is involved.

Merits and Demerits

In lens antenna, feed and feed support do not obstruct the aperture, as the rays are transmitted away from the feed.

It has greater design tolerance i.e., a larger amount of wrapping and twisting is possible in lens antenna as the wave enters one side emerges at the other side, maintaining the electrical path length.

It can be used to feed off the optical axis and is hence useful in applications where the beam is required to be moved angularly w.r.t. axis.

Lenses are usually bulky, and heavy.

This antenna is complicated in design.

It is costlier for the same gain and bandwidth in comparison with reflectors.

Application

The unstopped dielectric lens is a wideband antenna as its shape does not depend on the wavelength and hence can be used over a wide frequency range.

Lens antennas are commonly used above 1000 MHz.

It is a microwave device, is performed to be used usually above 3000 MHz and not below.

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Lens Antenna |Features and applications