Lens antenna

To generate narrow beams, the lens must be much larger than the wavelength of the radio waves, so lens antennas are mainly used at the high frequency end of the radio spectrum, with microwaves and millimeter waves, whose small wavelengths allow the antenna to be a manageable size.

The lens can be made of a dielectric material like plastic, or a composite structure of metal plates or waveguides.

[4] They are used less than parabolic antennas due to chromatic aberration and absorption of microwave power by the lens material, their greater weight and bulk, and difficult fabrication and mounting.

The lens is cut down to a uniform thickness in concentric annular (circular) steps, keeping the same surface angle.

To test Maxwell's theory that light was electromagnetic waves, these researchers concentrated on duplicating classic optics experiments with short wavelength radio waves, diffracting them with wire diffraction gratings and refracting them with dielectric prisms and lenses of paraffin, pitch and sulfur.

[11] In 1889 Oliver Lodge and James L. Howard attempted to refract 300 MHz (1 meter) waves with cylindrical lenses made of pitch, but failed to find a focusing effect because the apparatus was smaller than the wavelength.