THE TYPES OF THE ANTENNA ARE
1. Yagi uda antenna.
2. Folded dipole antenna.
3. Helical antenna.
4. Horn antenna.
1.YAGI UDA ANTENNA:
A yagi uda antenna consists of the one driven element , one reflector & one or more directors.
· The input is supplied to the driven element so it is known as the active element.
· For reflectors and directors we are not applying any input .so the reflectors and directors are called as parasitic elements.
· Driven element and parasitic elements are placed parallel to each other and close to each other.
· The reflector is placed back side of the driven element which is longer than driven element and compare to the all element . The element infront of the driven element is director which is smaller than all elements.
2.FOLDED DIPOLE ANTENNA:
Two half wave dipoles folded and joint each other then the folded dipole is formed . One dipole is in continuous and another is break at the centre to feed the input.
· The advantage of the folded dipole antenna is it will provide high resistance in compared to normal dipole.
· The length of the dipole is lambda/2 and the spacing between the two dipole is very small.
· Due to applied voltage %u201CV%u201D the current %u201CI/2%u201D is flowing through each dipole.
Helical antenna is broadband vhf & uhf antenna . It provides CIRCULAR POLARIZATION.
· Consider a thick copper wire or tube is wounded in the form of helix.
· The input to the helix is given to the coaxial cable the inner conductor of coaxial cable is connected to helix and outer is connected to the ground.
HELICAL ANTENNA IS OPERATED IN TWO MODES
1. NORMAL MODE:
In the normal mode the maximum radiation is perpendicular to the axis of the helix . So it is called %u201CNORMAL MODE OR PERPENDICULAR MODE%u201D.
· The normal mode is obtained when the values of helix are very small in compared to wavelength i.e., N,S<<LAMBDA.
2. AXIAL MODE:
In axial mode the maximum radiation occurs parallel to the axis of the helix.
· The axial mode is occurs when the diameter of helix are approximately equal to the wave length.
· The circumference of helix is around one wave length and spacing between the turns around PI/4.
4.HORN ANTENNA :
Horn antenna is a wave guide of different cross section which flared (or) tampered into large opening is called as the horn antenna . One end is exicted and another end is opened.When a wave guide is used as a antenna it cannot radiates due to the mismatch of impedance wit free space . By flaring the one end we are getting the impedance matching as well as high directivity.
TYPES OF HORN ANTENNA :
Basically we have two types of horn antenna they are
· RECTANGULAR HORN ANTENNA.
· CIRCULAR HORN ANTENNA.
1.RECTANGULAR HORN ANTENNA:
Based on the direction of the flaring angle again the rectangular horn antenna classified into SECTORIAL and PYRAMIDAL HORN ANTENNA.
· Again sectorial horn antenna is divided into two parts they are E-PLANE and H-PLANE based on the direction of the E & H PLANE.
2.CIRCULAR HORN ANTENNA:
Based on the direction of the flaring angle again the circular horn antenna classified into CONICAL HORN ANTENNA and BIDIRECTIONAL HORN ANTENNA.