PRIVATE AND CONFIDENTIAL

© CommScope

1

Horizontal Pattern Blooming with combined E-tilt and M-tilt

Base Station Antenna Systems

PRIVATE AND CONFIDENTIAL

© CommScope

2

Pattern Blooming is distortion or widening of the azimuth pattern as viewed on the horizon when mechanical downtilt is applied.

From work done a number of years ago using vertically polarized antennas, a “rule of thumb” was generated to give customers an idea of how much mechanical downtilt is acceptable. Note – these antennas incorporated no electrical downtilt.

The “rule of thumb” stated:

What is meant by Pattern Blooming?

To insure that the azimuth pattern as viewed on the horizon does not bloom by more than 10%, never

mechanically downtilt a given antenna more than one-half of its

vertical beamwidth.

This presentation will provide updated information on downtilting.

PRIVATE AND CONFIDENTIAL

© CommScope

4

Why does Blooming happen?

Pattern Analogy: Rotating a Disk

Mechanical Tilt Causes:

• Beam Peak to Tilt Below Horizon

• Back Lobe to Tilt Above Horizon

• No Tilt at ± 90°

PRIVATE AND CONFIDENTIAL

© CommScope

5

Illustration of Horizontal Pattern change with Mechanical Tilt

0

10

20

30

40

50

60

70 80 90 100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250 260 270 280

290

300

310

320

330

340

350

0

10

20

30

40

50

60

70 80 90 100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250 260 270 280

290

300

310

320

330

340

350

8° 0° 10° 6° 4° Mechanical Tilt

Elevation Pattern Horizontal Pattern

PRIVATE AND CONFIDENTIAL

© CommScope

6

Solving the Blooming issue using Electrical Downtilt

For the radiation pattern to show maximum gain in the direction

of the horizon, each stacked dipole must be fed from the signal

source “in phase”. Feeding vertically arranged dipoles “out of

phase” will generate patterns that “look up” or “look down”.

The degree of beam tilt is a function of the phase shift of one

dipole relative to the adjacent dipole.

GENERATING BEAM TILT

Dipoles Fed “In Phase” Dipoles Fed “Out of Phase”

Exciter Phase

Energy

in

Exciter

PRIVATE AND CONFIDENTIAL

© CommScope

7

Why is there no Blooming using Electrical Downtilt?

Pattern Analogy: Forming a cone out of a disk

Electrical Tilt Causes:

• Beam peak to tilt below horizon

• Back lobe to tilt below horizon

• At ± 90° to tilt below horizon

• All the pattern tilts

“Cone” of the Beam Peak pattern

PRIVATE AND CONFIDENTIAL

© CommScope

8

Illustration of Horizontal Pattern change with Electrical Tilt

Elevation Pattern Horizontal Pattern

0

10

20

30

40

50

60

70 80 90 100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250 260 270 280

290

300

310

320

330

340

350

8° 0° 10° 6° 4° Electrical Tilt

0

10

20

30

40

50

60

70 80 90 100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250 260 270 280

290

300

310

320

330

340

350

PRIVATE AND CONFIDENTIAL

© CommScope

11

Method used to analyze Combinations of E-tilt & M-tilt

• A series of patterns are shown for a typical 4 foot antenna.

• The measured combinations of E-tilt and M-tilt are plotted as a function of each antenna’s vertical beamwidth (VBW).

• Best fit curves for 10% and 20% blooming were generated.

• The blooming curves for various antennas have different slopes.

• Graphs are included showing the azimuth beam squint as a function of only E-tilt and only M-tilt for several models.

• X-pol antennas squinted more rapidly as a function of mechanical downtilt than V-pol antennas.

• A graph of Sector Power Ratio vs E-tilt and M-tilt for several models is included.

“…the future focus of future technology enhancements should be on

improving system performance aspects that improve and maximize the

experienced SNR in the system…” Rysavy Research, September 2005

PRIVATE AND CONFIDENTIAL

© CommScope

12

15° M-tilt

5° M-tilt

Horizon

Gain reduction of X

dB on the horizon

using mechanical

downtilt occurs

much more rapidly

when electrical

downtilt is employed

Comparisons With and Without Electrical Downtilt

Horizon X X

Without Electrical Downtilt With Electrical Downtilt

Similar gain reduction

on the horizon as a

result of mechanical

downtilt causes

similar azimuth

pattern blooming

12° E-tilt

PRIVATE AND CONFIDENTIAL

© CommScope

13

Horizontal Pattern Shapes for Various M-tilts

PRIVATE AND CONFIDENTIAL

© CommScope

14

63°

LNX-6512 @ M-tilt = 0, E-tilt = 0

PRIVATE AND CONFIDENTIAL

© CommScope

15

LNX-6512 @ M-tilt = 0, E-tilt = 7

63º

PRIVATE AND CONFIDENTIAL

© CommScope

16

LNX-6512 @ M-tilt = 7, E-tilt = 0

69º

PRIVATE AND CONFIDENTIAL

© CommScope

17

LNX-6512 @ M-tilt = 7, E-tilt = 4

74°

PRIVATE AND CONFIDENTIAL

© CommScope

18

LNX-6512 @ M-tilt = 7, E-tilt = 7

80°

PRIVATE AND CONFIDENTIAL

© CommScope

19

LNX-6512 @ M-tilt = 11, E-tilt = 3

91°

PRIVATE AND CONFIDENTIAL

© CommScope

20

LNX-6512 @ M-tilt = 14, E-tilt = 0

100°

PRIVATE AND CONFIDENTIAL

© CommScope

21

6 dB Overlap Angle & Crossover Rolloff Comparisons

M( )E( ) Tilt Angle Crossover

M0E0 & M0E7 ---- 17° 10 dB

M7E7 ---------------- 25° 6 dB

M14E0 -------------- 29° 4 dB

PRIVATE AND CONFIDENTIAL

© CommScope

25

New “Rules of Thumb” for Mechanical Tilting of Antennas

To insure that the azimuth pattern of a typical antenna - as viewed on the horizon - does not bloom

by more than 10%, never mechanically downtilt a given antenna more than the amount calculated by

the equations below:

65º HBW M-tilt10% Bloom = (VBW – E-tilt)/2.5

Other HBW antennas follow different rules.

33º HBW M-tilt10% Bloom = (VBW – E-tilt)/1.5

90º HBW M-tilt10% Bloom = (VBW – E-tilt)/3.3

PRIVATE AND CONFIDENTIAL

© CommScope

26

k-Factor vs Rated Azimuth Beamwidth

Mechanical Downtilt

Factor for 10% Horizontal Blooming

1.0

1.5

2.0

2.5

3.0

3.5

30 35 40 45 50 55 60 65 70 75 80 85 90

Rated Azimuth Beamwidth (deg)

k F

acto

r

k vs HBW

Xº HBW M-tilt10% Bloom = (VBW – E-tilt)/k

PRIVATE AND CONFIDENTIAL

© CommScope

27

Beam Squint

-3 dB +3 dB

Squint θ/2

θ

Horizontal Boresight

θ

What is it?

The amount of azimuth (horizontal) or elevation

(vertical) pointing error of a given beam

referenced to mechanical boresite.

Why is it useful?

The beam squint can affect the sector

coverage if it is not at mechanical

boresite. It can also affect the

performance of the polarization

diversity style antennas if the two

arrays do not have similar patterns.

How is it measured?

It is measured using data collected

from antenna range testing.

What is Andrew standard?

For the horizontal beam, squint shall be less than 10% of the

3 dB beamwidth. For the vertical beam, squint shall be less than

15% of the 3 dB beamwidth or 1 degree, whichever is greatest.

PRIVATE AND CONFIDENTIAL

© CommScope

28

Azimuth Pattern Squint vs E-tilt

Beam Peak (Bisected at 3dB)

Max and Min over Band vs E-tilt

(M-tilt = 0)

-8

-6

-4

-2

0

2

4

6

8

0% 20% 40% 60% 80% 100%

E-tilt (percent of VBW)

Ma

x a

nd

Min

Sq

uin

t (d

eg

ree

s)

48 in X-pol Squint

48 in X-pol Squint

48 in V-pol Squint

48 in V-pol Squint

PRIVATE AND CONFIDENTIAL

© CommScope

29

Azimuth Pattern Squint vs M-tilt

Beam Peak (Bisected at 3 dB)

Max and Min over Band vs M-tilt

(E-tilt = 0)

-8

-6

-4

-2

0

2

4

6

8

0% 20% 40% 60% 80% 100%

M-tilt (percent of VBW)

Max a

nd

Min

Sq

uin

t (d

eg

rees)

48 in X-pol 850

48 in X-pol 850

48 in V-pol 850

48 in V-pol 850

PRIVATE AND CONFIDENTIAL

© CommScope

30

Sector Power Ratio (SPR)

What is it?

SPR is a ratio expressed in percentage

of the power outside the desired sector

to the power inside the desired sector

created by an antenna’s pattern.

Why is it useful?

It is a percentage that allows comparison

of various antennas. The better the SPR,

the better the interference performance of

the system.

How is it measured?

It is mathematically derived from the

measured range data.

What is Decibel Products standard?

Andrew Directed Dipole™ style antennas have

SPR’s typically less than 2 percent.

PUndesired

SPR (%) = X 100

PDesired

60

300

Σ

60

300 Σ

120°

DESIRED

UNDESIRED

PRIVATE AND CONFIDENTIAL

© CommScope

31

Sector Power Ratio vs E-tilt

Sector Power Ratio vs E-tilt

M-tilt = 0

0

2

4

6

8

10

12

14

16

0% 20% 40% 60% 80% 100%

M-tilt (percent of VBW)

SE

cto

r P

ow

er

Rati

o (

%)

48 in X-pol 850

96 in X-pol 850

48.5 in V-pol 850

E

PRIVATE AND CONFIDENTIAL

© CommScope

32

Sector Power Ratio vs M-tilt

Sector Power Ratio vs M-tilt

E-tilt = 0

0

2

4

6

8

10

12

14

16

0% 20% 40% 60% 80% 100%

M-tilt (percent of VBW)

Secto

r P

ow

er

Rati

o (

%)

48 in X-pol 850

96 in X-pol 850

48.5 in V-pol 850

PRIVATE AND CONFIDENTIAL

© CommScope

33

Summary

New technologies such as LTE will be more dependant on optimal network signal-to-noise (SNR) ratios.

One aspect strongly influencing these optimal SNRs is the correct choice of base station antennas.

Best network optimization is accomplished by using antennas with adjustable electrical downtilt.

Mechanical downtilting can cause larger sector overlap angles and non-optimal rolloff at the sector overlap points

The old “rule of thumb” concerning maximum mechanical downtilt does not apply when electrical downtilt is employed.

Squint and Sector Power Ratio are also compromised when mechanical downtilt is used.