Attachment Rad Haz Study 6.1m

This document pretains to SES-LIC-20111230-01503 for License on a Satellite Earth Station filing.

IBFS_SESLIC2011123001503_931547

Radiation Hazard Study 6.1 m Cassegrain Feed Earth Station ku-band Antenna This analysis predicts the radiation levels around a earth station 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, Section 2 Prediction Methods, Aperture Antennas, 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 environment. 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 Parameters Antenna diameter 6.1 m Antenna Isotropic gain 57 dBi Maximum Transmit Power 30 Watts Number of carriers 2 or more Nominal Frequency 14250 MHz In the following sections, the power density in the above regions, as well as other critically important areas will be calculated and evaluated. X2nsat, Inc. Radiation Hazard Study – 6.1m ku 30 December 2011 Page 1 of 5

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 given by the equation (1). (1) Lnf = D²/(4λ) Where Lnf = length to end of the near field, Where D = antenna diameter Where λ = wavelength at 14.250 GHz = 21.0 x10-3 meters or 21 cm From equation (1) it is found that the distance to the end of the near field is 442 meters. The maximum power flux density in the near field PDnf is given by: (2) PDnf = 16 Pt ŋ/(πD²) Where Pt is the maximum power transmitted by the amplifier (30 Watts). Where ŋ = Antenna Efficiency Antenna efficiency can be estimated, or a reasonable approximation for circular apertures can be obtained from the ratio of the effective aperture area to the physical area as follows: ŋ = (Gλ²/4π)/(πD²/4) = Gλ²/(π²D²) = 0.60 Where G = the on-axis gain of the antenna (57 dBi at 14.250 GHz) From equation (2), we see that PDnf = 0.25 mW/cm² Evaluation Uncontrolled Environment Complies with FCC Limit of 1 milliwatt per square centimeter Controlled Environment Complies with FCC Limit of 5 milliwatts per square centimeter X2nsat, Inc. Radiation Hazard Study – 6.1m ku 30 December 2011 Page 2 of 5

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 power density in the near field region, as shown above, will not exceed 0.25 mW/cm². Evaluation Uncontrolled Environment Complies with FCC Limit of 1 milliwatt per square centimeter Controlled Environment Complies with FCC Limit of 5 milliwatts per square centimeter On-axis Far-Field Region Free-space power density is maximum on-axis, varies inversely with the square of the of the distance and may be calculated from equation (3). (3) PDff = GPt/(4π R²) Where PDff = the power flux density on-axis in the far field, R = the distance to the far field region and is found from equation (4). (4) R = 0.6D²/λ From equation (4) it is found that the distance to the far field is 1060 meters. And, PDff is found from equation (3) as follows: PDff = 0.11 mW/cm² Evaluation Uncontrolled Environment Complies with FCC Limit of 1 milliwatt per square centimeter Controlled Environment Complies with FCC Limit of 5 milliwatts per square centimeter X2nsat, Inc. Radiation Hazard Study – 6.1m ku 30 December 2011 Page 3 of 5

Region Between Feed Flange and Reflector Transmissions from the feed horn are directed toward the reflector surface, and are confined within a conical shape defined by the feed. The energy between the feed and reflector surface can be calculated by determining the power density at the feed flange. This can be accomplished as follows: Power Density at Feed Flange, PDfeed = 4*Pt/Fa Where Fa = Area of Feed Window = π*Df²/4 Where Df = 15 cm Fa = 177 cm² PDfeed = 679 mW/cm² The energy between the feed horn and reflector 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 have received training specifying this area as a high exposure area. Procedures are established that assure that the transmitter is turned off before access by maintenance personnel to this area. Main Reflector Region The power density in the main reflector region is determined in the same manner as the power density at the feed flange, above, but the area is now the area of the reflector aperture: Power Density at Reflector Surface, PDreflector = 4*Pt/Sa Where Sa = Surface Area of Reflector = 29 m² PDreflector = 0.41 mW/cm² Evaluation Uncontrolled Environment Complies with FCC Limit of 1 milliwatt per square centimeter Controlled Environment Complies with FCC Limit of 5 milliwatts per square centimeter Off-axis Levels at the Far Field Limit and Beyond In 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 on-axis center line and the point of interest. The on- axis main-beam will be the location of the greatest of these maxima. The on-axis power density calculated above represent the maximum exposure levels that the system can produce. Off-axis power densities will be considerably less and hence comply with FCC limits. X2nsat, Inc. Radiation Hazard Study – 6.1m ku 30 December 2011 Page 4 of 5

Off-axis Levels at the Near Field and in the Transition Region 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 (20dB) 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 = 0.002 mW/cm² Evaluation Uncontrolled Environment Complies with FCC Limit of 1 milliwatt per square centimeter Controlled Environment Complies with FCC Limit of 5 milliwatts per square centimeter Evaluation of Safe Occupancy Area in Front of Antenna The area not be accessed remains the area between the feed horn and the reflector as indicated on page 4, the transmitter is turned off before access by maintenance personnel to this area. This area will not be accessible to the general public, as fencing will be installed around the antenna for general safety and security purposes. This will prevent any non-authorized access to the beam axis. Conclusion Based on the above analysis it is concluded that harmful levels of radiation will not exist in regions accessible to the general public or to the earth station’s operating personnel. Study Prepared by: Phil Kratchanov x2nsat RF Engineer phil@x2nsat.com X2nsat, Inc. Radiation Hazard Study – 6.1m ku 30 December 2011 Page 5 of 5


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Document Modified: 2019-04-21 06:20:36
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