Attachment Radiation Analysis

This document pretains to SES-LIC-20110119-00039 for License on a Satellite Earth Station filing.

IBFS_SESLIC2011011900039_861376

RADIATION HAZARD ANALYSIS 9.3 meter EARTH STATION This analysis calculates the non-ionizing radiation levels due to transmission from the earth station. The Office of Engineering and Technology (OET) Bulletin, No. 65 Edition, specifies that the Maximum Permissible Exposure (MPE) limit for persons in a General Population/Uncontrolled environment to non-ionizing radiation is a power density equal to 1 milli-watt per centimeter squared averaged over a thirty minute period, and for a controlled environment is 5 milli-watts per centimetersquared averaged over a six minute period. The analysis estimates the maximum power density levels in the vicinity of the antenna for six regions: near field; far field; transition zone; near the reflector surface; between the reflector and the ground; and between the sub-reflector and the main reflector. A brief discussion for each region is given below and the results of the analysis are summarized. The attached table shows the assumptions, formulae and calculations for all cases. 1. NEAR FIELD REGION The near field (or Fresnel region) is essentially a cylindrical volume with its axis co-incident with the antenna boresight. The base of this volume is the same as the aperture of the antenna. According to OET Bulletin No. 65, its length is equal to the square of the diameter divided by four times the wavelength. Past the boundary of the Near Field region, the power density from the antenna decreases linearly with respect to increasing distance. 2. TRANSITION REGION The transition region between the near field and the far field regions will have a power density that essentially decreases inversely with increasing distance. In any case, the maximum power density in this region will not exceed the maximum value calculated for the near field region, for the purpose of evaluating potential exposure. 3. FAR FIELD REGION The far field (or Fraunhofer region) extends outwards from a distance equal to 0.6 times the square of the reflector diameter divided by the wavelength, according to OET Bulletin No. 65. Power density varies inversely as the square of the distance. The maximum value of the power density is calculated using the equation given in the Bulletin. 4. REGION BETWEEN THE MAIN REFLECTOR AND SUB-REFLECTOR Transmissions from the feed assembly are directed toward the sub-reflector surface, and are reflected back toward the main reflector. The most common feed

assemblies are waveguide flanges, horns or sub-reflectors. The energy between the sub-reflector surfaces can be calculated by determining the power density at the sub- reflector surface. This is done by taking four times the power divided by the sub- reflector surface area. 5. REGION NEAR MAIN REFLECTOR SURFACE The power density in the region near the main reflector surface can be estimated as equal to four times the power divided by the area of the main reflector surface, assuming that the illumination is uniform and that it would be possible to intercept equal amounts of energy radiated towards and reflected from the reflector surface. 6. REGION BETWEEN MAIN REFLECTOR AND GROUND The power density in the region between the main reflector and the ground can be estimated as equal to the power divided by the area of the reflector surface, assuming uniform illumination over the surface of the reflector. 7. RESULTS OF ANALYSIS The radiation analyses in the following Table was performed in accordance with the discussion from the previous sections and assuming worst case operating conditions. Based on the analysis contained therein it is concluded that levels of radiation in excess of 1 mW/cm2 will exist in each of the regions defined. Therefore, a perimeter fence will be constructed around the antenna to create a controlled environment for areas that could otherwise be occupied by the general public. As can be seen, the analysis further demonstrates that the calculated radiation levels exceed the controlled environment level of 5 mW/cm2 for all areas. As a consequence of this, the transmitter will be turned off during antenna maintenance and proper signage will be included at antenna fence perimeter entry points in order that earth station personnel will not be exposed to radiation levels exceeding the FCC MPE of 5.0 mW/cm2.

RADIATION HAZARD ANALYSIS Nomenclature Formula Value Unit INPUT PARAMETERS D = Antenna Diameter 9.3 meters d = Diameter of Subreflector 0.99 meters P = Max Power into Antenna 4169 Watts η = Apperture Efficiency 53 % F = Frequency 17800 MHz λ = Wavelength 300/F 0.0169 meters CALCULATED VALUES A = Area of Reflector pi*D^2/4 67.93 meters^2 a = Area of Subreflector pi*d^2/4 0.77 meters^2 l = Length of Near Field D^2/4λ 1282.94 meters L = Beginning of Far Field 0.6D^2/λ 3079.04 meters G = Antenna Gain @ F (n=100% max value) η(pi*D/λ)^2 1592718.44 linear Antenna Gain in dB 10*log(G) 62.02 dBi POWER DENSITY CALCULATIONS Max Power Density In Region Hazard Assessment Region Formula Value (mW/cm^2) (FCC MPE Limit=1 mW/cm^2) 1. Snf = Max Near Field Power Density 4*η*P/A 13.01 >FCC MPE Limit (See Text) 2. Sff = Max Far Field Power Density G*P/(4*pi*L^2) 5.57 >FCC MPE Limit (See Text) 3. Max Transition Region Power Density <= Nr Fld Region 13.01 >FCC MPE Limit (See Text) 4. Near Main Reflector Surface 4*P/A 24.55 >FCC MPE Limit (See Text) 5. Between Main Reflector and Subreflector 4*P/a 2156.66 >FCC MPE Limit (See Text) 6. Between Main Reflector and Ground P/A 6.14 >FCC MPE Limit (See Text)


Document Created: 2011-01-18 14:46:31
Document Modified: 2011-01-18 14:46:31
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