Helical Antenna
Helical Antenna
Helical Antenna
(Helix Antenna)
BHAVIN V KAKANI
IT-NU
Introduction
The radiating element is a helix of wire, driven at one end and radiating along the
axis of the helix.
A ground plane at the driven end makes the radiation unidirectional from the far
(open) end.
There are different types of ground plane:
Flat ground plane
Cylindrical cavity
Frustrum cavity
Modes of Operation
Normal
Mode
NL<<
Axial Mode
D = diameter of helix
N = number of turns
C = circumference of helix = D
= pitch angle
S = L sina = C tana
The input impedance is critically dependent upon the pitch angle and
size of the conducting wire.
Normal/Perpendicular Mode
Even though the RP of the loop and short dipole are same their
polarizations are at right angles.
AR =1 Circular Polarization
Radiating field is maximum in the end fire direction or along the axis of
helix
polarization of wave is either circular or nearly circular
This mode is possible if the circumference is selected of the order of
one wavelength and spacing is selected approx. equal to pie/4.
this mode, the antenna gain and beam width both depend on the
In
length of helix i.e. N.S
3. Design a 10 turn helical antenna so that at the center frequency of 10 GHz, the
circumference of each turn is 0.95. Assuming a pitch angle of 14o,
determine the
a. mode in which the antenna operates
b. half-power beamwidth (degrees)
c. directivity in dB.
Answer: Axial mode, HPBW=36o , D=15dB
5. Calculate