Base Station Antenna Systems 2008 Product Selection Guide - AVW
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Base Station Antenna Systems 2008 Product Selection Guide - AVW

Base Station Antenna Systems 2008 Product Selection Guide - AVW Base Station Antenna Systems 2008 Product Selection Guide - AVW

avw.co.nz
12.07.2015 Views

Applications/Engineering NotesAntenna FundamentalsBeam SquintThe amount of pointing error of a given beam referenced to mechanical boresite.The beam squint can affect the sector coverage if it is not at mechanical boresite. Itcan also affect the performance of the polarization diversity style antennas if the twoarrays do not have similar patterns.Horizontal Beam TrackingRefers to the beam tracking between the two beams of a ±45° polarization diversityantenna over a specified angular range.For optimum diversity performance, the beams should track as closely as possible.Sector Power Ratio (SPR)SPR is a ratio expressed in percentage of the power outside the desired sector to thepower inside the desired sector created by an antenna’s pattern.It is a percentage that allows comparison of various antennas. The better the SPR,the better the interference performance of the system.MechanicalBoresiteSquintHorizontal BoresiteElectricalBoresite–3 dB350 0 103402033030 +3 dB320403105030060290702808027090260100250110240120230130220140210150200190 180 17016000/2120° Beam Squint120°3203103002902802702602502402302203302103402003501900180101702030150160401405060708090100110120130DesiredUndesired–45°Array3503403303203103002902802702602502402302202102001900180101702030405060708090100110120130140150160+45°Array Sector Power Ratio300P Undesired Horizontal Beam Tracking60SPR (%) = ————— X 100 60P Desired 300Andrew Wireless Solutions www.andrew.com123

Applications/Engineering NotesAntenna Fundamentals65°90°The ImpactLower Co-Channel Interference/Better Capacity and QualityIn a three sector site, traditional antennas produce a high degree of imperfect power control orsector overlap. Traditional Flat PanelsImperfect sectorization presents opportunities for: Increased softer hand-offs Interfering signals65° Directed Dipole TM90° Dropped calls Reduced capacityThe rapid roll-off of the lower lobes of the Directed Dipole TM antennas create larger, better defined“cones of silence” behind the array. Much smaller softer hand-off area Dramatic call quality improvement 5% –10% capacity enhancement120˚ Sector Overlay IssuesFor network optimization, much emphasis has been placed on improved elevation (vertical) patternshaping, such as downtilt, null fill and upper sidelobe suppression. References from two technicalpapers are shown below that support the fact that azimuth pattern shaping can also play a large rolein network optimization.“. . . From the numerical results, the user capacities are dramatically decreased as the imperfectpower control increases and the overlap between the sectors (imperfect sectorization) increases . . .”The quote noted above was used in the following technical paper:“On the Capacity and Outage Probability of a CDMA Hierarchial Mobile System with Perfect/ImperfectPower Control and Sectorization ”By: Jie ZHOU et al., IEICE TRANS FUNDAMENTALS, VOL.E82-A, NO.7 JULY 1999Percentage ofcapacity loss (dB)1510500 5 10 15Overlapping angle (degree)The graph shown above was used in the following technical paper:“Effect of Soft and Softer Handoffs on CDMA System Capacity”By: Chin-Chun Lee et al., IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 47, NO. 3, AUGUST 1998Parameters like improved azimuth pattern rolloff beyond the 3 dB points and improved front-to-backratio—both co-polarization and cross-polarization—are key features. The goal is to have enoughsector-to-sector overlap to accommodate desired handoffs, while minimizing the excess overlapwhich can result in interference. In CDMA type systems this shows up as pilot pollution, while in GSMsystems it can show up as unwanted coverage. The excerpt graph shown above presents a quantitativemeasure of how this overlapping angle can affect capacity loss in a CDMA network. Qualitatively,excessive overlay also reduces capacity of TDMA and GSM systems.124Andrew Wireless Solutions www.andrew.com

Applications/Engineering Notes<strong>Antenna</strong> FundamentalsBeam SquintThe amount of pointing error of a given beam referenced to mechanical boresite.The beam squint can affect the sector coverage if it is not at mechanical boresite. Itcan also affect the performance of the polarization diversity style antennas if the twoarrays do not have similar patterns.Horizontal Beam TrackingRefers to the beam tracking between the two beams of a ±45° polarization diversityantenna over a specified angular range.For optimum diversity performance, the beams should track as closely as possible.Sector Power Ratio (SPR)SPR is a ratio expressed in percentage of the power outside the desired sector to thepower inside the desired sector created by an antenna’s pattern.It is a percentage that allows comparison of various antennas. The better the SPR,the better the interference performance of the system.MechanicalBoresiteSquintHorizontal BoresiteElectricalBoresite–3 dB350 0 103402033030 +3 dB320403105030060290702808027090260100250110240120230130220140210150200190 180 17016000/2120° Beam Squint120°3203103002902802702602502402302203302103402003501900180101702030150160401405060708090100110120130DesiredUndesired–45°Array3503403303203103002902802702602502402302202102001900180101702030405060708090100110120130140150160+45°Array Sector Power Ratio300P Undesired Horizontal Beam Tracking60SPR (%) = ————— X 100 60P Desired 300Andrew Wireless Solutions www.andrew.com123

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