ADTRAN 6000 Series System Manual

Also see for TRACER 6000 SERIES: User manual

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ADTRAN 6000 Series System Manual Manual pdf 25 page image

TRACER 6000 Series Integrated System Manual Section 2 Microwave Path Engineering Basics612806420L1-1F Copyright © 2005 ADTRAN, Inc. 25Antenna Beam PatternsAntennas used with the TRACER 64x0 system have a particular beam shape, determined in part by thephysical construction and geometry of the antenna. The antenna beam patterns are characterized by adominant main lobe, which is the preferred lobe to use for point-to-point communications, and several sidelobes, as shown in Figure 2. When setting up a microwave link, antenna alignment is nothing more thansteering the main lobes of both antennas until the main lobe of one transmitter is centered on the receivingelement of the receiving antenna.Figure 2. Typical Antenna Beam PatternAntennas are also designed to radiate RF energy efficiently for a specific range of frequencies. Pleaseconsult the data sheet for your particular antenna make and model to ensure that it is specified to operate inthe 2400 MHz to 2483.5 MHz (TRACER 6410) or 5725 MHz to 5850 MHz (TRACER 6420) frequencybands for your TRACER 64x0 system.Fresnel Zones, Earth Curvature, and Antenna HeightsFresnel zones correspond to regions in the microwave path where reflections of the intended signal occurand combine in both constructive and destructive manners with the main signal, thereby either enhancingor reducing the net power at the receiver.In general, the odd numbered Fresnel zones (1, 3, 5, ...) add constructively at the receiver, while the evennumbered Fresnel zones (2, 4, 6, ...) add destructively at the receiver.The first Fresnel zone corresponds to the main lobe, 60 percent of which must be free of physicalobstructions for the path calculations to be valid. Since the main lobe contains the vast majority of themicrowave energy, this zone is typically used to determine proper antenna heights when placing antennason towers or buildings.The curvature of the Earth becomes a legitimate obstruction for path lengths of 7 miles (11 kilometers) orgreater, and must also be accounted for when determining minimum antenna heights.The aggregate expression for minimum antenna height that incorporates both the 60 percent first Fresnelzone and the Earth’s curvature is given bymain lobeside lobesh 72.1 d4f----- 0.125d2+= (feet)