The document discusses helical antennas, which consist of a conductor wound into a helical shape above a ground plane. Helical antennas provide circular polarization and are used at very high and ultra-high frequencies. The construction of a helical antenna involves parameters like length, number of turns, diameter, circumference, pitch angle, and distance from the ground plane. It can operate in either a normal mode or an axial mode, and the axial mode is generally used. Applications of helical antennas include AM broadcasting, reducing AC line noise, and low-frequency uses like RFID and airport door controls.

1. Dr. S.MUTHUMANICKAM
Associate Professor
Department of ECE
1
EC8701 ANTENNAS
AND
MICROWAVE ENGINEERING PART III
HELICAL ANTENNA

2. 2
HELICAL ANTENNA
Conductor is wound into helical shape and with respect
to ground is helical antenna
Properties:
1. Provides circular polarization
2. Uses very high frequency and ultra high
frequencies

3. 3
CONSTRUCTION OF HELICAL ANTENNA
L = length of one turn = √S² +(Πd)²
N = Number of turns
D = Diameter of helix
C = Circumference (πD)
α = Pitch angle = tan⁻1(S/πD)
l = Distance between helix and
ground plane.

4. 4
Pitch angle

5. 5
AXIAL MODE this
mode is generally
used
OPERATING MODE
1. Normal Mode
2. Axial Mode
C < λ

6. 6

7. 7

8. 8

9. 9

10. 10

11. 11

12. 12
Conventional helix antenna composed of a wire and a
ground plane: (a) antenna model and scheme; (b) normal
mode of radiation; (c) axial mode of radiation

13. 13
HELICAL ANTENNA in
AXIAL MODE
Helical antenna
Major lobe
Minor lobes

14. 14

15. 15

16. 16

17. 17

18. 18
Applications
AM broadcast
Null down AC line noise
Decreases TV sweep noise
harmonics
Low frequency applications:
RFID, Gate Parking, Airport
door controls

19. 19