Attachment Radhazrre.pdf

This document pretains to SES-LIC-20080115-00051 for License on a Satellite Earth Station filing.

IBFS_SESLIC2008011500051_615351

Radiation Hazard Report Page 1 of 4 Analysis of Non-Ionizing Radiation for a 3.7-Meter Earth Station System This analysis predicts the radiation levels around a proposed earth station complex, comprised of one aperture (reflector) type antenna. This report is developed in accordance with the prediction methods contained in OET Bulletin No. 65, Evaluating Compliance with FCC Guidelines for Human Exposure to Radio Frequency Electromagnetic Fields, Edition 97-01, pp 26-30. The maximum level of non-ionizing radiation to which employees may be exposed is limited to a power density level of 5 milliwatts per square centimeter (5 mW/cm2) averaged over any 6 minute period in a controlled environment and the maximum level of non-ionizing radiation to which the general public is exposed is limited to a power density level of 1 milliwatt per square centimeter (1 mW/cm2) averaged over any 30 minute period in a uncontrolled evironment. Note that the worse-case radiation hazards exist along the beam axis. Under normal circumstances, it is highly unlikely that the antenna axis will be aligned with any occupied area since that would represent a blockage to the desired signals, thus rendering the link unuseable. Earth Station Technical Parameter Table Antenna Actual Diameter 3.7 meters Antenna Surface Area 10.8 sq. meters Antenna Isotropic Gain 52.8 dBi Number of Identical Adjacent Antennas* 1 Nominal Antenna Efficiency (ε) 65% Nominal Frequency 14000 MHz Nominal Wavelength (λ) 0.0214 meters Maximum Transmit Power / Carrier 200 Watts Number of Carriers 1 Total Transmit Power 200 Watts W/G Loss from Transmitter to Feed 0.15 dB Total Feed Input Power 193 Watts Near Field Limit Rnf = D²/4λ = 160 meters Far Field Limit Rff = 0.6 D²/λ = 383 meters Transition Region Rnf to Rff * The Radiation Levels will be increased directly by the number of antennas indicated, on the assumption that all antennas may illuminate the same area. In the following sections, the power density in the above regions, as well as other critically important areas will be calculated and evaluated. The calculations are done in the order discussed in OET Bulletin 65. In addition to the input parameters above, input cells are provided below for the user to evaluate the power density at specific distances or angles. 1.0 At the Antenna Surface The power density at the reflector surface can be calculated from the expression: PDrefl = 4P/A = 7.19 mW/cm² (1) Where: P = total power at feed, milliwatts A = Total area of reflector, sq. cm In the normal range of transmit powers for satellite antennas, the power densities at or around the reflector surface is expected to exceed safe levels. This area will not be accessible to the general public. Operators and technicians will receive training specifying this area as a high

Radiation Hazard Report Page 2 of 4 exposure area. Procedures will be established that will assure that all transmitters are rerouted or turned off before access by maintenance personnel to this area is possible. 2.0 On-Axis Near Field Region The geometrical limits of the radiated power in the near field approximate a cylindrical volume with a diameter equal to that of the antenna. In the near field, the power density is neither uniform nor does its value vary uniformly with distance from the antenna. For the purpose of considering radiation hazard it is assumed that the on-axis flux density is at its maximum value throughout the length of this region. The length of this region, i.e., the distance from the antenna to the end of the near field, is computed as Rnf above. The maximum power density in the near field is given by: PDnf = (16ε P)/(π D²) = 4.65 mW/cm² (2) from 0 to 160 meters Evaluation Uncontrolled Environment: Mitigation Required Controlled Environment: Complies to FCC Limits 3.0 On-Axis Transition Region The transition region is located between the near and far field regions. As stated in Bulletin 65, the power density begins to vary inversely with distance in the transition region. The maximum power density in the transition region will not exceed that calculated for the near field region, and the transition region begins at that value. The maximum value for a given distance within the transition region may be computed for the point of interest according to: PDt = (PDnf)(Rnf)/R = dependent on R (3) where: PDnf = near field power density Rnf = near field distance R = distance to point of interest For: 160 < R < 383 meters We use Eq (3) to determine the safe on-axis distances required for the two occupancy conditions: Evaluation Uncontrolled Environment Safe Operating In F-F region, See Distance,(meters), Rsafeu: Section 4 Controlled Environment Safe Operating 149 Distance,(meters), Rsafec: 4.0 On-Axis Far-Field Region The on- axis power density in the far field region (PDff) varies inversely with the square of the distance as follows: PDff = PG/(4πR²) = dependent on R (4) where: P = total power at feed G = Numeric Antenna gain in the direction of interest relative to isotropic radiator R = distance to the point of interest For: R > Rff = 383 meters PDff = 1.99 mW/cm² at Rff We use Eq (4) to determine the safe on-axis distances required for the two occupancy conditions: Evaluation

Radiation Hazard Report Page 3 of 4 Uncontrolled Environment Safe Operating Distance,(meters), 541 Rsafeu : Controlled Environment Safe Operating Distance,(meters), See Section Rsafec : 3 5.0 Off-Axis Levels at the FarField Limit and Beyond Ipn the far field region, the power is distributed in a pattern of maxima and minima (sidelobes) as a function of the off-axis angle between the antenna center line and the point of interest. Off- axis power density in the far field can be estimated using the antenna radiation patterns prescribed for the antenna in use. Usually this will correspond to the antenna gain pattern envelope defined by the FCC or the ITU, which takes the form of: Goff = 32 - 25log(Θ) for Θ from 1 to 48 degrees; -10 dBi from 48 to 180 degrees (Applicable for commonly used satellite transmit antennas) Considering that satellite antenna beams are aimed skyward, power density in the far field will usually not be a problem except at low look angles. In these cases, the off axis gain reduction may be used to further reduce the power density levels. For example: At one (1) degree off axis At the far-field limit, we can calculate the power density as: Goff = 32 - 25log(1) = 32 - 0 dBi = 1585 numeric PD1 deg off-axis = PDffx 1585/G = 0.0166 mW/cm² (5) 6.0 Off-Axis power density in the Near Field and Transitional Regions According to Bulletin 65, off-axis calculations in the near field may be performed as follows: assuming that the point of interest is at least one antenna diameter removed from the center of the main beam, the power density at that point is at least a factor of 100 (20 dB) less than the value calculated for the equivalent on-axis power density in the main beam. Therefore, for regions at least D meters away from the center line of the dish, whether behind, below, or in front under of the antenna's main beam, the power density exposure is at least 20 dB below the main beam level as follows: PDnf(off-axis) = PDnf /100 = 0.047 mW/cm² at D off axis (6) See page 5 for the calculation of the distance vs elevation angle required to achieve this rule for a given object height. 7.0 Region Between the Feed Horn and Sub-reflector Transmissions from the feed horn are directed toward the subreflector surface, and are confined within a conical shape defined by the feed horn. The energy between the feed horn and subreflector is conceded to be in excess of any limits for maximum permissible exposure. This area will not be accessible to the general public. Operators and technicians should receive training specifying this area as a high exposure area. Procedures must be established that will assure that all transmitters are rerouted or turned off before access by maintenance personnel to this area is possible. Evaluation of Safe Occupancy Area in Front of Antenna The distance (S) from a vertical axis passing through the dish center to a safe off axis location in front of the antenna can be determined based on the dish diameter rule (Item 6.0). Assuming a flat terrain in front of the antenna, the relationship is: S = (D/ sin α) + (2h - D - 2)/(2 tan α) (7) Where: α = minimum elevation angle of antenna D = dish diameter in meters h = maximum height of object to be cleared, meters

Radiation Hazard Report Page 4 of 4 For distances equal or greater than determined by equation (7), the radiation hazard will be below safe levels for all but the most powerful stations (> 4 kilowatts RF at the feed). For D= 3.7 meters h= 2 meters Then: α S 10 16.5 meters 15 11.1 meters 20 8.5 meters 25 6.9 meters 30 5.9 meters 22 7.8 meters 45 4.4 meters Suitable fencing or other barrier will be provided to prevent casual occupancy of the area in front of the antenna within the limits prescribed above at the lowest elevation angle required. The applicant will ensure that the main beam of the antenna will be pointed at least one diameter away from any buildings, or other obstacles in those areas that exceed the MPE levels. Since one diameter removed from the center of the main beam the levels are down at least 20 dB, or by a factor of 100, public safety will be ensured. The earth station will marked with the standard radiation hazard warnings, as well as the area in the vicinity of the earth station, to inform those in the general population, who may be working or otherwise present on the roof, and in or near, the main beam of the antenna. Finally, occupational exposure will be limited, and the transmitter will be turned off during periods of maintenance, so that the MPE standard of 5.0 mw/cm**2 will be complied with for those regions in close proximity to the main reflector, and subreflector, which could be occupied by operating personnel. In addition, the earth station will only be in use for an eight hour period per week, thus limiting its potential impact on the general public.


Document Created: 2008-01-14 07:59:26
Document Modified: 2008-01-14 07:59:26
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