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Antenna Installations Guideline (Version 1.0)

The intent of this document is to provide some generic guidelines for antenna installations at a basestation in a cellular system. In the following, we will address the isolation and the space diversityrequirements for an antenna installations for AMPS-A and AMPS-B, ETACS and TACS, ETACSand GSM.

Exceptions will apply when AMPS and ETACS or AMPS and GSM systems are co-locating at a sametower location.

Isolation

By isolation, we are talking about the signal attenuation from one transmitting antenna to thereceiving end of another antenna installed at a base station. The isolation needs to be at lease 40 dB

between a transmitting and a receiving antenna, and at least 20 dB between two transmit antennas.

In order to achieve the desired isolation values, the antennas have to be placed at a certain minimumdistance from each other. This distance is dependent upon the antenna type and the mounting

configuration. In general, omni directional antennas require greater horizontal distance than thedirectional antennas, and the vertical separation provides much greater isolation compared tohorizontal separation.

Diversity

Diversity that we talk about here is the space diversity at the receiving antenna. When the radiosignals are received by two separate antennas, the signal which normally varies due to deep fadingcan be overcome by having two receive antennas with un-correlated signals. By the use of receivediversity, it assures that at least one of the two signals will be out of a deep fade.

The diversity gain increases with distance, but in practice the separation distance is usually limiteddue to space constraints on a tower. Diversity gain is highest in the direction which is perpendicularto the line between the two receive antennas and is lowest when the two receive antennas are in-linewith the radiating direction.

Separation Spacing Requirement for Antennas

The minimum isolation requirement for two antenna are:

Tx - Tx 20 dBTx - Rx 40 dB

, the wavelength to be used for the separation distance calculation is,

(inches) = 11808 / Freq (Mhz) and

(meters) = 300 / Freq (Mhz)

1. Horizontal Antenna Spacing,

S

Tx Antenna Rx Antenna

Decoupling in dB +

22 20 log ( )s

G GT R

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Above equation is valid fors

> 10 and GT

and GR

< 10 dB

2. Vertical or Collinear Antenna Separation,

S

Isolation in dB +

28 40logs

Typically 1 < S and dBmax 70 dB

S is spacing between ends ofradiatingportions of the antennas.

3. Combined Horizontal and Vertical Separation

SH

SV

S (dB) = (V-H) 90 + H

where, S is Slant IsolationV is Vertical IsolationH is Horizontal Isolation

is angle between the antennas

The preceding information was taken from Celwave Product Selection Guide 195. For additionalinformation, please refer to pages 296 and 297.

Diversity Receive Antenna Spacing

For diversity reception, omni directional antennas must be spaced apart according to the following:

h

d 13

where h is the antenna height and d is the separation distance. There is no need to go beyond 30feet separation regardless of height, although greater separation is permissible. Also, the two receiveomnidirectional antennas should be positioned in such a way that the main coverage area is in adirection roughly normal to the line connection the two antennas.

The above information was taken from Autoplex document 401-200-300.

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Other Separation Requirements

AMPS-TACS/ETACS/GSM - Please refer to RF Engineering Guidelines for Operating an AMPSand TACS/ETACS System in the Same Service Area. Document # 54452-921222-01M

ETACS-GSM - Please follow guidelines as supplied in this document.

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