Test 1: Co-channel interference at the mobile unit

Test 2: Co-channel interference at the cell site

Lowering the Antenna Height

(a) on a high hill

(b) in a valley

In a Forested Area

Reduction of Co-channel interference in a cellular mobile system

• Increasing the separation between two co-channel cells

• Using directional antennas at the base station

• Lowering the antenna heights at the base station.

Reduction of Co-channel Interference by Means of a Notch in the Tilted Antenna Pattern 

A seven-cell cellular configuration

Antenna Pattern

Vertical Beamwidth

Horizontal Beamwidth

33°,45°,65°,85°

A typical pattern for a directional antenna of 120° beamwidth 

(a) Azimuthal pattern of 8-dBdirectional  antenna

A typical pattern for a directional antenna of 120° beamwidth 

(b) Vertical pattern of 8-dB directional antenna

Antenna Tilting

• In general, the vertical pattern of an antenna radiates the main energy towards the horizon

• Only that part of the energy which is radiated below the horizon can be used for the coverage of the sector

• Downtilting the antenna limits the range by reducing the field strength in the horizon

Mechanical Downtilting

Mechanical Downtilt

Mechanical Downtilt

The Effect of Mechanically Downtilting Antenna on the Coverage Pattern

Vertical antenna pattern of a 120° directional antenna

Notch appearing in tilted antenna pattern

Mechanical Downtilting

• is the down tilt angle• d1 is the length of the upper

antenna-mounting arm• d2 is the length of the lower

antenna-mounting arm• h is the distance between d1

and d2

Antenna ParametersMechanical Downtilt  Electrical Downtilt

• HBW gets bigger

• Causes gain reduction

• HBW remains the same

• But can’t adjust downtilt (fixed)

Suggested Method for Reducing Interference

Umbrella-pattern Effect

• Antenna in which the waves are guided downward in all directions from a central pole or tower to the ground, somewhat like the ribs of an open umbrella.