Waves & antennas

SIGNAL--FREQUENCY & WAVE LENGTH

ELECTROMAGNETIC WAVE

Electric field –voltage changes occurring in the RF antenna which is radiating the signal

Magnetic field– changes in the current flow

WHAT IS ANTENNA ?

Photons -- Electrons Electrons -- Photons

RADIATION MECHANISM

ELECTROMAGNETIC WAVE

SIMPLE DIPOLE ANTENNA

RESONANCE

POLARIZATION EM waves are composed

of two planes – vertical and horizantal (E and M fields)

If the s/g is Txed in one polarization , must be Rxed in same polarization

Otherwise attenuation

When the wave is in V-plane – V-polarization H-plane– H-polarization

TYPES OF POLARIZATION

ELECTROMAGNETIC SPECTRUM

WAVES USED IN TELECOMMUNICATION

Radio waves Radiated by the

Omnidirectional antennas

Transmits UHF frequencies

Micro waves Radiated by the

directional antennas Transmits 0.3GHz-

300GHz

ANTENNAS FOR RADIO WAVES

Omni directional antennas for horizantal plane

Also called sector antennas For multipoint side of point to multipoint

applications Beam width 45-180 degrees

ANTENNAS FOR RADIO WAVES

RADIATION PATTERN OF RF ANTENNA

ANTENNAS FOR MICRO WAVES

ANTENNAS FOR MICRO WAVES Low power mw sources –

FET, Tunnel , Impatt, Gunn diodes

High power mw sources – magnetron , klystron, TWT, gyrotron

Used for point to point communications

Shorter wavelengths and high frequencies

Antenna size is inversily proportional to the transmitted frequency

Allowing frequency reuse

PATCH ANTENNA USED IN MOBILES

CONSTRUCTION OF PATCH ANTENNA Simple patch antenna

uses one half wave length

two metallic plates separated by a dielectric layer.

Metalic plates made of copper

Antenna is fed by 50ohm transmission line

Generation of E and H fields dependent on length and width of the patch and wavelength

E AND H FIELDS OF A PATCH E-field

varies along the length of the patch

minimum at the centre and maximum at the edges

The H-field varies along the length is

in a direction perpendicular to the E-field.

maximum at the center and minimum at the edges.

The impedance is zero at the center of the patch

PATCH ANTENNA RADIATION PATTERN

PATCH ARRAY ANTENNA RADIATION PATTERN

RADIATION PATTERN FROM A CELL PHONE

RADIATION FROM MOBILE PHONE