Introduction to Antenna Design

tobascothwackUrban and Civil

Nov 15, 2013 (4 years and 8 months ago)


Introduction to Antenna



A device that radiates or intercept
electromagnetic waves is called an

An antenna not necessarily perform
equally well in all directions.

Radiation Pattern

A polar diagram indicates how well an
antenna transmits or receives in different
directions .

Beam Width

The angle within which the power radiated
is above one
half of what it is in the most
preferential direction.

Antenna Resistance

Radiation Resistance.

A factious resistance which would be
dissipate as much power as the antenna in
question is radiating if it were connected to
the same transmission line.

Ohmic Resistance.

Actual loss in term of heat

Due to conversion of electrical

nergy into heat.

Antenna as resonant circuit

The impedance presented by an antenna
has a reactive component due to currents
and voltages being out of phase.

As the frequency of the signal being
presented to the antenna is changed, the
impedance presented to the transmission line
become reactive, just as with a tuned circuit.

Bandwidth = f
/ Q

Velocity Factor

The velocity of electromagnetic waves is
slightly different in a conductor such as the
material the antenna is made of:aluminium,
copper etc.

The velocity factor is that number which
when multiplied by the speed of light in the
free space gives us the speed of light in the
medium in question

Antenna Types

Some of the important antennas are
discussed as follow.

Wave Dipole and Marconi Antennas

Beam Antennas

Folded dipole Antennas

Turnstile Antennas

Loop Antennas

Antenna Gain

A comparison of the output, in a particular
direction, of the antenna in question and a
reference antenna. (Reference is generally an
omnidirectional antenna)

A antenna with let say 10 db gain means that
the antenna in question improves upon the
reference antenna in that direction by 10 db.

Frequently, one antenna is compared to the
other, avoiding the need of a reference.

Back Ratio

The ratio expressed in db of the output in
the most optimum direction to the output
180 degree away from the optimum

Reflectors and Directors

Reflectors and directors are additional
conducting elements used to obtain
improved directivity of an antenna.

The directors are placed in front and
reflectors are placed in back of the
antenna in question.

Antenna Traps

It is often desirable that a
station transmits different
frequencies effectively
using same transmission line
and antenna .

It can be achieved by
installing different units
called trap (LC networks)
at different places along
the antenna which
changes length of antenna

Wave Propagation

The radiated signal travels along one of the
following routes

1)Along the ground (Ground Wave)

2)Straight out in a straight line (Line

3)Up to the ionosphere and back to earth (Sky

Maximum distance between transmitter and
receiver is given as

Where hr and ht are heights of transmitting
and receiving antenna respectively

2 2
d h h
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Antenna Modeling Software

Antenna Modeling Software


Antenna Magus

VE3SQB Programs


EZNEC antenna design tool

Remcom Tools

Numerical Technique of HFSS

works on
finite element method

Finite Element Analysis (FEA) is a numerical method which provides solutions to
problems that would otherwise be difficult to obtain

FEA uses a complex system of points called


which make a grid called


This mesh is programmed to contain the material and structural
properties which define how the structure will react to certain loading conditions.
Nodes are assigned at a certain density throughout the material depending on
the anticipated stress levels of a particular area. Regions which will receive large
amounts of stress usually have a higher node density than those which
experience little or no stress. Points of interest may consist of: fracture point of
previously tested material, fillets, corners, complex detail, and high stress areas.
The mesh acts like a spider web in that from each node, there extends a mesh
element to each of the adjacent nodes. This web of vectors is what carries the
material properties to the object, creating many elements