27-08-2012, 01:08 PM
LENS ANTENNA
[attachment=32825]
Lens Antenna may be divided into two distinct types
Delay lenses,in which the electrical path length is increased by the lens medium
Fast lenses,in which the electrical path length is decreased by the lens medium
Dielectric lenses and H-plane metal-plate lenses are of the delay type.
E-plane metal plate lenses are of fast type
Non metallic Dielectric Lens Antennas.(Fermats principle)
This type is similar to the optical lens. It may be designed by the ray analysis methods of geometrical optics.
The field over the plane surface can be made everywhere in phase by shaping the lens so that all paths from the source to the plane are of equal electrical length.This is the principle of equality of electrical path length(Fermats principle)
Artificial Dielectric Lens Antennas
Artificial dielectric consists of discrete metal particles of macroscopic size.
The size of the metal particles should be small compared to the design wavelength to avoid resonance effects.
The particles may be metal spheres,disks,
strips or rods.
Rotman lens antenna
They are very useful as multiple beam forming networks for a linear array antenna.A Rotman lens has three focal points,and the shape of the focus for the position of exciting elements between those focal points are given by a circular arc.Therefore ,when exciting elements between focal points are excited,phase errors on the aperture of linear array antenna occur which need to be minimized.
Advantages of lens antenna
In lens antenna,the rays are transmitted away from the feed system,hence the aperture is not obstructed due to the feed and feed support.
In lens antenna,as the waves enter from one side and leaves out from other end,greater extent of wrapping and twisting is possible without disturbing electrical path length.
Lens antenna can be used to feed at a point off the axis;so it is most extensive used in applications where beam is needed to be moved angularly with respect to axis.
Disadvantages of lens antenna
The disadvantages of lens antennas are as follows.
Lens antennas are bulkier.
Design of lens antennas is complicated.
Compared with reflectors,lens antennas are expensive for the same gain and bandwidth requirements.
Applications of lens antenna
As lens antenna is a microwave antenna,it is most widely used at a microwave frequency above 3000 mhz.
For larger bandwidth requirements, unstepped dielectric lens is used because its shape is not dependent on wavelength.For narrow bandwidth applications dielectric lens antennas are used.
[attachment=32825]
Lens Antenna may be divided into two distinct types
Delay lenses,in which the electrical path length is increased by the lens medium
Fast lenses,in which the electrical path length is decreased by the lens medium
Dielectric lenses and H-plane metal-plate lenses are of the delay type.
E-plane metal plate lenses are of fast type
Non metallic Dielectric Lens Antennas.(Fermats principle)
This type is similar to the optical lens. It may be designed by the ray analysis methods of geometrical optics.
The field over the plane surface can be made everywhere in phase by shaping the lens so that all paths from the source to the plane are of equal electrical length.This is the principle of equality of electrical path length(Fermats principle)
Artificial Dielectric Lens Antennas
Artificial dielectric consists of discrete metal particles of macroscopic size.
The size of the metal particles should be small compared to the design wavelength to avoid resonance effects.
The particles may be metal spheres,disks,
strips or rods.
Rotman lens antenna
They are very useful as multiple beam forming networks for a linear array antenna.A Rotman lens has three focal points,and the shape of the focus for the position of exciting elements between those focal points are given by a circular arc.Therefore ,when exciting elements between focal points are excited,phase errors on the aperture of linear array antenna occur which need to be minimized.
Advantages of lens antenna
In lens antenna,the rays are transmitted away from the feed system,hence the aperture is not obstructed due to the feed and feed support.
In lens antenna,as the waves enter from one side and leaves out from other end,greater extent of wrapping and twisting is possible without disturbing electrical path length.
Lens antenna can be used to feed at a point off the axis;so it is most extensive used in applications where beam is needed to be moved angularly with respect to axis.
Disadvantages of lens antenna
The disadvantages of lens antennas are as follows.
Lens antennas are bulkier.
Design of lens antennas is complicated.
Compared with reflectors,lens antennas are expensive for the same gain and bandwidth requirements.
Applications of lens antenna
As lens antenna is a microwave antenna,it is most widely used at a microwave frequency above 3000 mhz.
For larger bandwidth requirements, unstepped dielectric lens is used because its shape is not dependent on wavelength.For narrow bandwidth applications dielectric lens antennas are used.