ANTENNA FUNDAMENTALS

ANTENNAS are metallic devices for radiating and transmitting

electromagnetic waves.

IEEE ‘a means for radiating and receiving radio waves’

They are used for transition between a guiding structure and free

space.

oZ : Characteristic impedance of the transmission line

AZ : Load impedance of the antenna

LR : Resistance due to the losses of the antenna (conduction and

dielectric losses associated with the antenna structure)

rR : Radiation resistance

AX : Reactance which represents the imaginary part of the impedance

associated with radiation by the antenna.

Ideally energy generated by the source should be transformed to rR

(which represents the radiation by the antenna)

ANTENNA TYPES

1) Wire Antennas

2) Aperture Antennas

3) Microstrip Antennas

4) Array Antennas

5) Reflectors Antennas

6) Lens Antennas

WIRE ANTENNAS

APERTURE ANTENNAS

MICROSTRIP PATCH ANTENNAS

ARRAY ANTENNAS

REFLECTOR ANTENNAS

LENS ANTENNAS

RADIATION

Wire is given as

The charge Q (C) within volume V is moving in the z- direction with a

uniform velocity zv (m/s). The volume charge density (C/m3) over the

cross section of the wire is given as:

ˆz v zJ a v

For an ideal conductor, the current density (A/m) resides on the surface

of the wire:

ˆs z s zJ a v

Where s is the surface charge density in (C/m2).

If the wire is very thin, then the current (A) in the wire can be

represented by:

z l zI v

Where l is the charge per unit length. For a time-varying current

z zl l z

dI dva

dt dt

Where z

z

dva

dt is the acceleration in ( m/s2). If the wire is of length l

then:

z zl l z

dI dvl l l a

dt dt

The above equation is the basic relation between the current and the

charge which serves as the fundamental relation of ELECTROMAGNETIC

RADIATION.

So, for radiation there must be:

1) Time varying current,

2) Acceleration (or deceleration) of charge.

Therefore:

1) If the charge is not moving, current is not created and there is no

radiation.

2) If the charge is moving with a uniform velocity:

a) There is no radiation if the wire is straight and infinity in extent.

b) There is radiation if the wire is curved, bent, discontinuous,

terminated or truncated.

3) If charge is oscillating in a time-motion, it radiates even if the wire

is straight.

WIRE CONFIGURATIONS FOR RADIATION

Curved Wire

CURRENT DISTRIBUTION OF TRANSMISSION LINE AND LINEAR DIPOLE