standards and guidelines for communication sites - Radio And ...
standards and guidelines for communication sites - Radio And ... standards and guidelines for communication sites - Radio And ...
ENVIRONMENTAL EVALUATION APPENDIX A: ELECTROMAGNETIC ENERGY INFORMATION FIGURE A-4 EXAMPLE OF NEAR FIELD/FAR FIELD CROSSOVER The data in Figure A-4 represent the crossover for a 6 dBd gain omni antenna that is 2.74 m (9 ft.) in length. As the aperture length and gain change, the crossover point will also change greatly. For the example above, the crossover point is approximately 9.14 m (30 ft.). For an antenna with 10 dBd of gain and an aperture length of 3.96 m (13 ft.), the crossover point will be over 30.5 m (100 ft.). A 3 dBd gain antenna with an aperture length of 457 mm (1.5 ft.) will have a crossover point of only 914 mm (3 ft.). A.2.3.1.1CYLINDRICAL MODEL For vertical antennas, with omnidirectional horizontal patterns, the power density in the near field can be estimated using the circular radiation pattern and the height of the antenna. The area of a cylinder placed over this antenna is assumed to be uniformly exposed to the power radiated by the antenna; no RF energy emanates from the top or bottom. This power density is approximately the same as the average power density an individual of a specific height would be exposed to when standing next to the antenna. This formula is referred to as the Cylindrical Model because it utilizes a cylinder for the modeling (see Figure A-5). FIGURE A-5 CYLINDRICAL MODEL S = -------------- P 2πDL S = Power Density (mW/cm 2 ) P = Total Power into Antenna (mW) D = Distance from Antenna (cm) L= Length of Antenna Aperture (cm) A-8 68P81089E50-B 9/1/05
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES ENVIRONMENTAL EVALUATION Shorter antennas result in higher fields and exposure for a constant power. The greater the power, the higher the EME field. The shorter the aperture, the higher the EME field. The closer to the antenna, the higher the EME field. A.2.3.1.2SPHERICAL MODEL In the far field, the radiation pattern becomes developed and does not change with distance from the antenna. The maximum radiating power density becomes related to the gain of the antenna. In the far field, the power density decreases as the square of the distance. With an isotropic point source (omnidirectional in all directions) the power density can be envisioned as the source power distributed over a sphere having a radius equal to the distance from the antenna. When the antenna has gain, the maximum power density in the far field can be calculated using the formula below: S = Power Density (mW/cm 2 ) P = Total Power into Antenna (mW) G = Gain Ratio of Antenna based on an Isotropic radiator D = Distance from Antenna (cm) A.2.3.2 ROOFVIEW EME MODELING SOFTWARE 1 RoofView is a modeling software package that allows a theoretical study of site situations. The software creates a mosaic map of the area showing the EME levels (see Figure A-6). The calculations can use different methods, different standards, antenna heights, and uptime for evaluation. There are two versions: • RoofView is the building version showing EME situations on a single plane. • TowerCalc is used to model towers. This will allow the EME situation on any level of the tower to be understood. The software runs on Excel 5.0 for Windows 3.1 and NT and Excel 7 for Windows 95. The information needed to create a model and generate a zoning map is: • Transmitter Power into Antenna • Frequency • Antenna mount designation 1. Trademark RoofView and TowerCalc are licensed to Richard Tell Associates, Inc., Las Vegas NV. Additional information can be found on Website: www.radhaz.com 68P81089E50-B 9/1/05 A-9 S = PG 4πD 2 -------------
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STANDARDS AND GUIDELINES FOR COMMUNICATION SITES ENVIRONMENTAL EVALUATION<br />
Shorter antennas result in higher fields <strong>and</strong> exposure <strong>for</strong> a constant power. The greater the<br />
power, the higher the EME field. The shorter the aperture, the higher the EME field. The closer<br />
to the antenna, the higher the EME field.<br />
A.2.3.1.2SPHERICAL MODEL<br />
In the far field, the radiation pattern becomes developed <strong>and</strong> does not change with distance from<br />
the antenna. The maximum radiating power density becomes related to the gain of the antenna.<br />
In the far field, the power density decreases as the square of the distance. With an isotropic point<br />
source (omnidirectional in all directions) the power density can be envisioned as the source<br />
power distributed over a sphere having a radius equal to the distance from the antenna. When the<br />
antenna has gain, the maximum power density in the far field can be calculated using the<br />
<strong>for</strong>mula below:<br />
S = Power Density (mW/cm 2 )<br />
P = Total Power into Antenna (mW)<br />
G = Gain Ratio of Antenna based on an Isotropic radiator<br />
D = Distance from Antenna (cm)<br />
A.2.3.2 ROOFVIEW EME MODELING<br />
SOFTWARE<br />
1 RoofView is a modeling software package that allows a theoretical study of site situations. The<br />
software creates a mosaic map of the area showing the EME levels (see Figure A-6). The<br />
calculations can use different methods, different <strong>st<strong>and</strong>ards</strong>, antenna heights, <strong>and</strong> uptime <strong>for</strong><br />
evaluation. There are two versions:<br />
• RoofView is the building version showing EME situations on a single plane.<br />
• TowerCalc is used to model towers. This will allow the EME situation on any level of the<br />
tower to be understood.<br />
The software runs on Excel 5.0 <strong>for</strong> Windows 3.1 <strong>and</strong> NT <strong>and</strong> Excel 7 <strong>for</strong> Windows 95. The<br />
in<strong>for</strong>mation needed to create a model <strong>and</strong> generate a zoning map is:<br />
• Transmitter Power into Antenna<br />
• Frequency<br />
• Antenna mount designation<br />
1. Trademark RoofView <strong>and</strong> TowerCalc are licensed to Richard Tell Associates, Inc., Las Vegas NV.<br />
Additional in<strong>for</strong>mation can be found on Website: www.radhaz.com<br />
68P81089E50-B 9/1/05 A-9<br />
S =<br />
PG<br />
4πD 2<br />
-------------
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