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Loop
Antenna
1
I EC2009001
2
Introduction
 Metallic
conductor bent into the shape of
a closed curve, such as a circle or a
square, with a gap in the conductor to
form the terminals
 Simple to construct, inexpensive & very
versatile
3
Properties
 Equivalent
to infinitesimal magnetic dipole
 Loop Antennas’ with small perimeters
have small Radiation Resistances(smaller
than their loss resistances)
 Not used in transmitting mode
 Responds to the magnetic field rather
than the electric field. Hence eliminates
Noise
4
Principle
 In
receiving applications it works on the
principle of the "differences" in voltages
induced by the current flowing in the sides
of the antenna.
 These difference voltages can be
extremely minute in amplitude and any
loop antenna usually requires an
associated amplifier capable of at least
25 dB power gain following it.
5
Why Loop Antenna


Radio Direction Finding
No available space for a longwire antenna:


Loop Antennas are small compared to wire
antennas
To eliminate noise:



Loop primarily responds to the magnetic
component of the radio wave
Noise resides primarily in the electrical
component
A vertical antenna responds mainly to the
electrical component.
6
Uses
 Used
as receivers in portable radios,
pagers where Signal-to-Noise ratio is
important than antenna efficiency.
 As probes for field measurements
 As directional antennas for radiowave
navigation
7
Classification
 Electrically
small
Circumference ≤ λ/10
 Electrically large
Circumference ≈ λ
8
Small Loop and Infinitesimal
Magnetic Dipole
A magnetic dipole of magnetic moment iml
is equivalent to a small electric loop of
radius a and constant electric current io
9
Ferrite Loop
 Radiation
Resistance of loop antenna is
very low
 Raised by increasing circumference
 Insert a Ferrite Core
 Increases Flux, Magnetic Field, Open
Circuit Voltage