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 FundamentalsHalf Power BeamwidthHalf power beamwidth (HPBW) is a parameter that measures the shape of the radiation pattern. It isthe angular width of the radiation pattern’s main lobe. It is measured between the points where thepower pattern is one-half (3 dB down) the main lobe’s peak value. HPBW is usually specified for thehorizontal and vertical radiation patterns. The exception to this is the horizontal pattern of an omnidirectionalantenna that is circular.Directivity can be estimated from the two principal plane HPBWs by using:For sector antennas (1):41250D (dBi) = 10*log10 –––––––––––––––––––––––––––––––––––For omnidirectional antennas (2):(0.53*HBW3dB+0.25*HBW10dB+18)*VBW3dBD 191.0 0.818 + 1/ V– 172.4where H= horizontal pattern half power beamwidth, degrees V= vertical pattern half power beamwidth, degreesThese formulas show that directivity increases as HPBW decreases.An assumption needs to be made concerning the efficiency or the losses associated with an antennato determine the gain. These formulas can then be used to ensure the appropriate gain has beenchosen for specified horizontal and vertical HPBWs.Andrew Wireless Solutions www.andrew.com121

Applications/Engineering NotesAntenna FundamentalsBack Lobe160170180190170180190130140150160200150140120120130110Front-to-BackRatio110100200210340330220320230310240300250260 270 280290100909080Horizontal PatternPolar Plot Center = -40 dB-3 dB level 5 dB/radial division10°/angular division80707060605050404030Side LobesNulls302020340100350100350Half PowerBeamwidth Figure 11 Horizontal Pattern Polar Plot showing HPBW and Front-to-Back RatioMain LobeMain Lobe MaximumNull FillFront-to-Back RatioThe front-to-back ratio is the ratio of the maximum directivity of anantenna (usually at = 0°, = 0° in the altazimuth coordinatesystem) to its directivity in a rearward direction antenna (usually at = 0°, = 180° in the altazimuth coordinate system). Figure 11shows the HPBW and front-to-back ratio for a typical horizontalpattern.Side Lobes and NullsA typical vertical pattern is shown in Figure 12. The main lobe (ormain beam or major lobe) is the lobe in which the direction of maximumradiation occurs. A number of minor lobes are found aboveand below the main lobe. These are termed side lobes. Betweenthese side lobes are directions in which little or no radiation occurs.These are termed nulls. Nulls may represent a 30 or more dBreduction (less than one-thousandth the energy of the main beam)in received signal level in that direction.Techniques exist to lower upper side lobes and redirect some ofthe radiating energy and fill in nulls. This is termed null fill. Often,the consequence of doing this is to widen the main lobe and thuslower the directivity and reduce the antenna’s gain.Cross-Polarization Ratio (CPR)CPR is a comparison of the co-polarized vs. cross-polarized patternperformance of a dual-polarized antenna generally over the sectorof interest (alternatively over the 3 dB beamwidth).It is a measure of the ability of a cross-polarized array to distinguishbetween orthogonal waves. The better the CPR, the betterthe performance of polarization diversity.210330220320230240250260 270 280290300310Polar Plot Center = -40 dB5 dB/radial division10/angular division Figure 12 Elevation Pattern Polar Plot showing Pattern Parameters120° 120°TypicalDirectedDipole Cross-Pol Ratio (CPR)Co-PolarizationCross-Polarization (Source at 90°)122Andrew Wireless Solutions www.andrew.com

Applications/Engineering Notes<strong>Antenna</strong> FundamentalsHalf Power BeamwidthHalf power beamwidth (HPBW) is a parameter that measures the shape of the radiation pattern. It isthe angular width of the radiation pattern’s main lobe. It is measured between the points where thepower pattern is one-half (3 dB down) the main lobe’s peak value. HPBW is usually specified for thehorizontal and vertical radiation patterns. The exception to this is the horizontal pattern of an omnidirectionalantenna that is circular.Directivity can be estimated from the two principal plane HPBWs by using:For sector antennas (1):41250D (dBi) = 10*log10 –––––––––––––––––––––––––––––––––––For omnidirectional antennas (2):(0.53*HBW3dB+0.25*HBW10dB+18)*VBW3dBD 191.0 0.818 + 1/ V– 172.4where H= horizontal pattern half power beamwidth, degrees V= vertical pattern half power beamwidth, degreesThese formulas show that directivity increases as HPBW decreases.An assumption needs to be made concerning the efficiency or the losses associated with an antennato determine the gain. These formulas can then be used to ensure the appropriate gain has beenchosen for specified horizontal and vertical HPBWs.Andrew Wireless Solutions www.andrew.com121

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