8/6/2019 ANTSYS

1/15

ANTENNA SYSTEM

HOW TO TEST

8/6/2019 ANTSYS

2/15

DEFINITIONS

Antenna

Jumper 1

Jumper 2

Connector 1Connector 2 Feeder

An antenna system is composed of:

an antenna;

a feeder;

connectors;

and optionally of one or two jumpers(*).

(*) = the better choice is to buy jumper assembled.

8/6/2019 ANTSYS

3/15

Why and what to test

An antenna system must be tested to be sure that it can transmit/receive radio frequency.

If it is not correctly tuned, the irradiated power/received signal could be decreased.

In order to verify the whole system, each component must be checked alone, and after

the entire antenna system will be measured.

8/6/2019 ANTSYS

4/15

Wrong way to test an antenna system (I)

Measure the Return Loss of the whole system at the far side of the antenna.

R.L. = R.L.(Ant) + (2 x Att.)

Where:R.L. = Return Loss (limit to be measured)

R.L.(Ant) = R.L. of the antenna (measured/specified by

manufacturer)

Att. = feeder (plus jumpers) attenuation measured/specified

at working frequency.

8/6/2019 ANTSYS

5/15

Wrong way to test an antenna system (II)

The previous formula is wrong because also the connectors, jumper(s) and feeder give

their contribution to the R.L.

They generate Return Loss themselves.

Again: with this formula, having a feeder with high attenuation, means the system musthave high R.L. value, but it is not possible to obtain a value so good.

8/6/2019 ANTSYS

6/15

A correct way to measure an antenna system

It is to take account of the reflection of every element.

Reflection is a vectorial size, with amplitude and phase: the worst case is when all

reflections are in phase.

One or more all in-phase contribution will certainly exist in a broadband system.

8/6/2019 ANTSYS

7/15

Calculation of expected R.L.

at input of antenna system (I)

You need the following info:

R.L. of jumper(s) (manufacturer);

R.L. of feeder (manufacturer);

R.L. of antenna (measured alone after installation);

Attenuation of jumper(s) (manufacturer);

Attenuation of feeder (measured alone at working frequency after

installation).

Note: if you need jumpers, buy them assembled from a manufacturer with R.L and

attenuation certification packing together.

8/6/2019 ANTSYS

8/15

Calculation of expected R.L.

at input of antenna system (II)

Convert all R.L. to power reflection coefficents(): = 10 -R.L./10

Convert all attenuations to power ratios (G):

G = 10 -Att./10

8/6/2019 ANTSYS

9/15

Calculation of expected R.L.

at input of antenna system (III)

Apply the following formula:

2tot= 2jump1+(1-2jump1)22conn1 G2jump1+(1-2jump1)2 (1-2conn1)22feed G2jump1+(1-2jump1)2 (1-2conn1)2(1-2feed)22conn2G2jump1G2feed+(1-2jump1)2 (1-2conn1)2(1-2feed)2(1-2conn2)22jump2 G2jump1 G2feed+(1-2jump1)2(1-2conn1)2(1-2feed)2(1-2conn2)2(1-2jump2)22antG2jump1G2feedG2jump2

Where: = reflection coefficent;G = attenuation;

jump1 orjump2 = jumper near equipment (1) or near antenna (2);

conn1 or conn2

feed = feeder.

8/6/2019 ANTSYS

10/15

Calculation of expected R.L.

at input of antenna system (IV)

Convert to R.L.:

R.L. = -10 log10(square root 2)

This will be the max R.L. value when all contributions are in phase condition.

8/6/2019 ANTSYS

11/15

Calculation in practice

Using the previous formula is not an easy and fast way for field engineer:

a good solution is to put all data in an excel file to obtain a graph which represents

R.L. vs feeder attenuation for a gived R.L. antenna value in working frequency band.

8/6/2019 ANTSYS

12/15

SOME HINTS

Buy jumpers assembled: each jumper must have R.L. test report;

ask for the graph R.L. vslength to the manufacturer about feeder for yourworking frequency;

;

check the feeder loss.

8/6/2019 ANTSYS

13/15

CONSIDERATIONS (I)

All values gived from manufacturers regarding connectors, feeders and

antennas are referred to best conditions: installing conditions will

. will

be degraded due the blending;

low value of R.L. also mean small amplitude of intermodulation products

generated by the system: this is important for multi carrier in a transmittingantenna system;

note that a small variation of R.L. will not have impact to coverage

(see table below);

Reference:

ETSI ETR 053

8/6/2019 ANTSYS

14/15

CONSIDERATIONS (II)R.L. (dB) % Reflected % Forward R.L. (dB) % Reflected % Forward

10,0 10,00 90,00 15,0 3,16 96,84

10,2 9,55 90,45 15,2 3,02 96,98

10,4 9,12 90,88 15,4 2,88 97,12

10,6 8,71 91,29 15,6 2,75 97,2510,8 8,32 91,68 15,8 2,63 97,37

11,0 7,94 92,06 16,0 2,51 97,49

11,2 7,59 92,41 16,2 2,40 97,60

11,4 7,24 92,76 16,4 2,29 97,71

11,6 6,92 93,08 16,6 2,19 97,81

11,8 6,61 93,39 16,8 2,09 97,91

12,0 6,31 93,69 17,0 2,00 98,0012,2 6,03 93,97 17,2 1,91 98,09

12,4 5,75 94,25 17,4 1,82 98,18

12,6 5,50 94,50 17,6 1,74 98,26

12,8 5,25 94,75 17,8 1,66 98,34

13,0 5,01 94,99 18,0 1,58 98,42

13,2 4,79 95,21 18,2 1,51 98,49

13,4 4,57 95,43 18,4 1,45 98,5513,6 4,37 95,63 18,6 1,38 98,62

13,8 4,17 95,83 18,8 1,32 98,68

14,0 3,98 96,02 19,0 1,26 98,74

14,2 3,80 96,20 19,2 1,20 98,80

14,4 3,63 96,37 19,4 1,15 98,85

14,6 3,47 96,53 19,6 1,10 98,90

14,8 3,31 96,69 19,8 1,05 98,95

8/6/2019 ANTSYS

15/15

IS IT ALL?

No, it is just the beginning:

an antenna system may have also tower mounting amplifier, power splitter, duplexer

filter, radiating cable...