This document summarizes the helical antenna. The helical antenna is a broadband VHF and UHF antenna that provides circular polarization. It consists of a helix of thick copper wire wound in a screw thread shape around a metal plate ground plane. The helix is fed by a coaxial cable connected to the inner conductor, while the outer conductor connects to the ground plane. The antenna can operate in two modes - normal mode and axial mode - depending on the helix diameter, turn spacing, and other dimensions. The normal mode radiates perpendicularly to the axis for circular polarization. The axial ratio and other parameters must meet certain conditions for effective circular polarization.

1. HELICAL ANTENNA
PREPARED BY
B.S.NAGESWARARAO
ASST PROF
ESWAR COLLEGE OF ENGINEERING
NARASARAOPET
GUNTUR
ANDHRA PRADESH
It is broad band VHF and UHF Antenna
It provide circular polarization

3. It contains HELIX of thick copper wire
or
Wounding in the shape of screw thread
Used as antenna in conjuction with
metal plate
Metal plate acts as ground plane

4. Helix is fed by coaxial cable
One end of helix connects to inner
conductor of coaxial cable
Outer conductor connects to the
ground plane

5. Mode of radiation depend on
Diameter of the helix D and turn
spacing S
Feed wire lies in the plane through
helix axis( between A and B)
Length of feed wire equal to S/2

6. Various dimensitions of helix

9. MODES OF OPERATION
1) NORMAL MODE (or) PERPENDICULAR MODE
2)AXIAL (or) BEAM MODE

10. Normal mode
 In this mode radiation pattern is same as
broad side array
 Perpendicular to the axis of helix
 Circular polarization
 This mode obtain when dimensions of helix
are less than LEMBDA

11.  SUCH SMALL HELIX BAND WIDTH NARROW AND RADIATION
EFIIENCY IS LOW

12.  RADIATION PATTERN IS COMBINATION OF SMALL DIPOLE
AND LOOP ANTENNA

14.  HELIX IS SERIES COMBINATION OF LOOP AND
DIPOLE ANTENNAS
 LOOP DIAMETER IS EQUAL TO HELIX
DIAMETER
 HELIX SPACE IS EQUAL TO LENGTH OF
DIPOLE

15.  RADIATION OF HELIX IN NORMAL MODE IS THE COMBINATION OF
DIPOLE AND LOOP RESPECTIVELY

18. AXIAL RATIO (AR)

19. WHEN

21.  THIS IS THE CONDITION FOR PITCH ANGLE
TO GET CIRCULAR POLARIZATION
 THIS MODE IS LIMITED USE BECAUSE OF LOW
BANDWIDTH AND RADIATION EFFIENCY

22. AXIAL MODE (CONDITIONS)

23. DESIGN PROCEDURE
IMPORTANT PARAMETERS
 BEAM WIDTH
 GAIN
 IMPEDENCE
 AXIAL RATIO

25. END