1. VHF, UHF and Microwave Antennas – II

2. LENS ANTENNA :-

3. TRANSMITTING MODE
RECEVING MODE

4. FUNCTIONS OF LENS ANTENNA
It controls the illumination of aperture.
It collimates the electromagnetic rays.
It provides directional characteristics.
In receiving mode ,it converges the incoming wave front at its focal point.
It produces plane wave front form a spherical wave front.

5. ANTENNA CONFIGURATIONS
Lens antenna with refractive index n>1
Lens antenna with refractive index n<1

6. LENS ANTENNAS CLASSIFIED AS
DEALY LENS
FAST LENS

7. Dielectric Lens There are two types of lens antenna
Delay lances (electrical path length increased by lens medium)
Ex. Dielectric lances, H plane metal-plate lenses
Fast lances (electrical path length decreased by lens medium)
Ex. E plane metal-plate lenses
Lens Antenna

8. Dielectric Lens There are two types of dielectric lenses Non Metallic
Metallic/artificial
Non Metallic Dielectric lens
This types is similar to optical lens
It may designed by ray analysis methods of geometrical optics.
Metallic or Artificial Dielectric lens
This types is less heavy compare to nonmetallic lens
It consist of discrete metal particles of macroscopic size.
Lens Antenna

9. Non Metallic Dielectric lens (Fermat’s Principle)
Lens Antenna

10. Non Metallic Dielectric lens (Fermat’s Principle)
Lens Antenna

11. Non Metallic Dielectric lens
Reflection Coefficient
Lens Antenna

12. Metallic/Artificial Dielectric lens
Lens Antenna

13. Reflector Lens Antenna

14. Polyrod
A dielectric rod or wire can act as a guide for EM waves. This tendency to radiate is turned to advantage in the polyrod antenna. (made of Polystyrene)
Lens Antenna

15. PRINCIPLE OF LENS ANTENNA

16. ZONING OF LENS(Z)
Curved surface zoning
Plane surface zoning

17. Advantages of zoing:- Dis advantages of zoing:-

18. Advantages of lens antenna
Lens are bulkier
Design of lens antenna is complicated
Lens are expensive

19. Applications of lens antennas
Lens antenna used as microwave antenna
For large bandwidth requirements unstepped dielectric lens antennas are used
For narrow bandwidth applications ,dielectric lens antennas are used

20. LUNEBURG LENS ANTENNA

21. EINSTEN’S GRAVITY LENS
The incident electromagnetic waves passing around stars are deflected through an angle which is proportional to mass of the star and then they brought into focus on the far side this is know as Einsten’s gravity lens