Antenna White Paper-Rev3

7/30/2019 Antenna White Paper-Rev3

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21dBi Antenna Case Study

Stockholm September 2004


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1. SUMMARY

Optimizing cellular networks in terms of CAPEX and OPEX is attractingincreased focus from cellular operators. This is particularly true forsystems operating on the higher frequency bands, i.e. GSM 1800/1900

and UMTS. The greatest impact is achieved by increasing the coverageof a site and thereby reducing the number of sites.

The coverage from a base station can be enhanced by increasing theoutput power in the downlink (base station to handset). However, the

maximum output power of the handset is limited and has a given range.Systems are hence typically referred to as being uplink limited (handsetto base station). Thus, downlink power in itself cannot increase coveragebeyond the limit set by the handset and the receive sensitivity of thebase station (BTS).

The signal of the handset is amplified by the base station and by

amplifying the signal already at the antenna by means of a TowerMounted Amplifier, TMA, the base station is able to process a signal that

would otherwise be too weak. Though the handset still performs at thegiven output power, the coverage area will be perceived to haveincreased thanks to the base station being able to handle the weakersignal.

While amplifiers amplify the signal in either up or downlink, antennasamplify the signal in both up- and downlink. This means that introducing

additional antenna amplification (gain) will increase the overall coveragearea irrespective of handset or BTS transmit power. As apposed to an

amplifier, an antenna is passive and low cost and the most cost effective

means of achieving coverage enhancement. Going from a typical 18dBiantenna to 21dBi offers a coverage advantage in the region of 30-40%.

Antenna gain is achieved by the radiating elements and the degree of

focusing of the antenna beam. Standard cell planning is based onantennas with half power beam width of 65 degrees opening angles.

High gain can be achieved by focusing beyond 65 degrees, e.g. 33degrees, but require special consideration in cell panning and BTShardware configuration.

A standard 18dBi antenna typically includes 8 radiating elements. Byadding additional elements the gain is increased. By doubling the

number of radiating elements to 16, a gain of 21dBi can in theory beachieved. The radiating elements are connected to a feed network thatdistributes the signal between the radiating elements within the

antenna. The feed network is typically made of coaxial cable or printedon a circuit board. Both these feed networks have inherent losses andthe longer the network is the greater the losses are. These losses offsetthe potential gain increase achieved by the addition of radiatingelements. In order to achieve the very high gain of 21dBi, a feed

network design with very low losses is required.


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By introducing a completely new feed network design philosophy,CellMax has been able to develop an antenna that fully harnesses thegain potential of the antenna, resulting in significantly betterperformance compared to existing antenna technology. This has beenachieved by developing a high efficiency antenna feed network thatreduces the power losses within the antenna to close to zero.

The low-loss feed network makes it possible to design a compact 2m21dBi antenna while keeping the vertical half-power beam-width of 4degrees with full beam shaping with regards to first upper side-lobesuppression and null-fill. The low-loss technology can further be appliedto design compact antennas (15 & 18dBi) for both rural and urban use.

The beam shaping performance gives excellent penetration close to theantenna, keeps the interference level low together with exceptional

coverage increase.

Operators using High Gain Antennas need to build fewer sites. Since themain part of the network rollout investment relates to the base stationsand switching network, the high-gain antenna is an efficient means oflowering CAPEX for the operator. Furthermore, an operator who hasfewer sites also has lower OPEX costs.

Increased geographical coverage by 30-40% compared to standard(18dBi) antennas

Potential reduction in the number of base stations of up to 30%. Possible CAPEX reduction in the range of 20 30% Corresponding OPEX reduction would also be achieved due to the

lower power consumption, site lease, O&M and transmission costs

Improved in-car coverage Improved indoor coverage Fewer dropped calls Improved call set-up success rate


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2 The CellMax 21 dBi High Gain Antenna

2.1 Radiation Diagrams

The diagrams below compare the radiation diagrams of an 18dBiantenna to the CellMax 21dBi antenna. The left diagram compares the

horizontal beam width and the right diagram the vertical beam width.

Fig 1: Radiation diagram comparison (logarithmic scale) between CellMax 21dBi

antenna (red) and a standard 18dBi antenna (blue)

Fig 2: Comparison of the radiated power between CellMax 21dBi antenna (blue)

and a standard 18dBi antenna (red), 3dB gain increase equals a doubling

of radiated power (linear scale).


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2.2 Feed Network Efficiency

The CellMax feed network efficiency is very high as is illustratedby the graph below. The gain curve comparison is between the

CellMax antenna and an antenna of similar length from a well-known antenna manufacturer. Almost 2dB more gain is achievedwith the CellMax low loss feed network compared to standard

technology.The measurements were carried out concurrently at a third partymeasurement range.

Fig 3: Gain comparison of the CellMax antenna and another antenna of similar

length

2.3 Vertical Opening Angle

Antenna gain is a function of the number of radiating elements andfocusing of the main beam. Adding radiating elements will increasefocusing in the vertical plane. Too much focusing results in a verynarrow vertical beam, which is not desirable since this may cause

coverage problems close to the antenna. It is therefore very importantto include null fills to overcome coverage problems close to site. Null fillon the other hand will reduce gain. It is therefore important to haveenough antenna gain in order not to degrade the desired performance.


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The diagram below is a comparison of a standard 18dBi antenna and a21dBi antenna using null fill. Though the signal strength is weaker thanthat of a standard antenna close to the site, it is significantly higher thanthe accepted design criteria and thus does not constitute any problem.The diagram also shows that in addition to increased range, the highersignal strength gives improved Grade of Service, i.e. increased callsuccess rate, less dropped calls, improved indoor and in-car penetration.

Fig 4: Received Signal Strength comparison between CellMax 21dBi antenna (red)

and a standard 18dBi antenna (blue).

2.4 Grade of Service

The increased signal strength increase is experienced throughout the celland will result in:

Improved indoor penetration Increased call setup success Rate and less dropped calls.

These improvements can be converted to increased revenue.


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3. Coverage Increase by 30-50%

High Gain (21dBi) Antennas gives a 3dB gain increase compared to

standard 18dBi antenna. 3dB gain increase means a doubling of theradiated power and received signal strength. This gain increase equals atheoretical coverage increase of ~50% but in practice 30-40%. Coverage

is calculated using the Okumura-Hata propagation model.

3.1 Okumura-Hata Propagation Prediction Model

The Okumura-Hata propagation prediction formula is based upon

empirical information obtained from measurements. The Hata formula isa mathematical fit for the Okumura graphical measurement data. TheOkumura-Hata equation for 1800, 1900 and 2100 MHz is given as below:

L = 46.3 + 33.9 log f - 13.82 log hb - a ( hm ) + [ 44.9 - 6.55 log hb ] log d - Lc

Factor RangeL path loss (dB )f frequency (MHz) .15 - 1.5 (2) GHzhb base antenna height (m) 30- 200 mhm mobile antenna height (m) 1 - 10 m

a ( hm ) = (1.1 log (f ) - 0.7 ) hm - ( 1.56 log (f ) - 0.8 )

mobile antenna height correctiond distance BTS - MS ( km ) 1 - 20 kmLc correction factor for various land usage/clutter

categoriesaddedtothe Hata formula

See the followingtable

The clutter class values [L c] that needs to be included in the RF prediction tools are asfollow:

Clutter class L c (dB)W Water 29

O1 Open, no obstructions 24

O2 Open, few obstructions 19

F1 Wood, low density with small trees or bushes 19

F2 Wood, mostly higher and more densely packed trees 9

S1 Low density suburban 11

S2 Leafy suburban 5

S3 Dense suburban 8

U1 Low density urban 3

U2 Dense urban 0


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3.2 Calculating Range

Based on the Okumuru-Hata model above, assumptions relating to

antenna position and environment the range increase can be calculatedas follows:

L = 46.3 + 33.9 log f - 13.82 log hb - a ( hm ) + [ 44.9 - 6.55 log hb ] log d - Lc

Where:

L=150 dB (standard 18 dBi antenna)hb= 30 m

hm= 1.5 mLc= 11 dB (S1, Low density suburban)

a ( hm )= (1.1 log (f ) - 0.7 ) hm - ( 1.56 log (f ) - 0.8 ) =

= (1.1 log (1800 ) - 0.7 ) 1.5 - ( 1.56 log (1800 ) - 0.8 ) = (3.58 0.7)*1.5 (5.08 0.8)= 4.32 - 4.28 = 0.04

L = 46.3 +33.9*log (1800)-13.82*log (30) 0.04 + [ 44.9 - 6.55 log (30)] log d 11

L = 46.3 + 110.35 20.41 0.04 + [ 44.9 9.68] log (d) 11

L = 125.20 + 35.22*log(d)

( )22.35

20.125log

=

Ld

= 22.3520.125

10

L

d ,

Therefore:

for L = 150, d = 5.06 km (18dBi antenna)

and

for L = 150 + 3 = 153 , d = 6.15 km dB (21dBi antenna),

This gives a >20% increase in range.


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3.3 Cell Coverage Area Calculation

3.3.1 Cell Area of a 3 Sector-Site

Standard cell panning is based on a grid comprising 3 sectors (cells) per

site. On a flat terrain, the coverage area of a 3 Sector site with anantenna beamwidth of 600 can be assumed as a close approximation tothree hexagons as shown below.

Area of a 3 sector site:

r

60deg

60

degrees

Area of a hexagon:

r

Area = r/2 cos 30 R/4= (r 2 3)/16

r/2

Area = 6 x area of each triangle is calculated as follows:

= (6 r 2 3)/16= (3 r 2 3)/8

Therefore the coverage area for a 3-sector site is (9 r2

3)/8.


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Therefore:

the area increase is:

48.106.5

15.6

8

39

8

39

2

2

22

2

1

22

2

1

===

=r

r

r

r

seAreaincrea

Conclusion

A 3 dB antenna gain increase gives a theoretical coverage increase of48%. Topography and other conditions may impact on this figure and inpractice the increase can be expected to be in the area of 30-40%

4. Other Applications

Besides the obvious application for the 21dBi antenna to increasecoverage, the following areas of use may also be considered.

4.1 Mast Height

The increase in antenna gain can be used to place the antenna at a lowerposition on a mast, or alternatively to build lower masts. The graphbelow illustrates the different antenna heights required to achieve the

same coverage based on a given signal strength requirement.


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Antenna height for equal signal strength (-90 dBm)

0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

100,0

500 1000 1500 2000 2500 3000 3500

Distance from site [m]

Antennaheight[m]

21 dBi

18 dBi

Fig 5: Received Signal Strength comparison between CellMax 21dBi antenna and a

standard 18dBi antenna.


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5. BUSINESS CASE

A cost comparison has been made comparing a standard base stationand establishment cost using a 18dBI antenna and the same using a

21dBi antenna. Based on a planned area of 100 sites for the referencecase, the cost savings are illustrated below.

Site reductions will also give a direct saving in Operation andMaintenance Costs, OPEX.

The business case assumes green-field deployment, i.e. siteestablishment cost.

5.1 Opportunities for Additional Cost Reductions/Savings

The following areas give scope for additional cost savings not included inthe business case.

Reduced connection fees in the RNC and switch if applicablethanks to fewer sites.

Transmission

The comparison includes base station equipment, antennas, TMAs andfeeders. In addition, site establishment including civil works, mast, and

power, cooling. Price is based on European levels.

Figure 14. Cost comparison table


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5.1 CONCLUSION

A 21dBi antenna offers great CAPEX savings at a very low cost to theoperator. Reduced number of sites will also reduce Opex.

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Antenna White Paper-Rev3