Problems And Exercises Wsv
1 Above 10 GHz, there are two additional degradations to path loss that we must take into account. What are they?
2 There are two frequency bands between 10 and 100 GHz that display high attenuation due to atmospheric gases. What bands are these? Which one displays excessively high attenuation, making it unusable for most earth-bound applications.
3 Discuss two practical applications of the high-loss band in question 2.
4 Argue why cumulative annual rainfall rates may not be used for calculation of excess attenuation due to rainfall and why, instead, we must use point rainfall rates.
5 In early attempts to build in sufficient margin on satellite and LOS microwave links operating above 10 GHz, it was found that the required margins were excessively large because we integrated excess attenuation per kilometer along the entire path (the entire path in the atmosphere for satellite links). Describe how statistics on rain cell size assisted to better estimate excess attenuation due to rainfall.
6 Why does excess attenuation due to rainfall and atmospheric gases increase as satellite elevation angle decreases?
7 When using linear polarization, one polarization displays considerably higher attenuation due to rainfall than the other polarization. Identify which polarization and explain why this is so.
8 In Chapters 2 and 3 we set a margin due to multipath fading. Is this margin additive to excess attenuation due to rainfall? Explain your answer.
9 What are the three variables we must deal with when calculating excess attenuation due to rainfall for microwave/millimeter wave LOS paths? Show how we relate these variables mathematically.
10 In rain region P for a certain location where the elevation angle was 5° and the desired time availability was 99.997%, we found excess attenuation values over 500 dB. What measures could be taken to drop this attenuation value to something more reasonable? Moving the earth station is not an option.
11 Calculate the specific attenuation per kilometer for a path operating at 30 GHz on a LOS basis with a time availability for the path of 99.9%. Neglect path length considerations, of course. The path is located in northeastern United States. Carry out the calculation for both horizontal and vertical polarizations.
12 Calculate the excess attenuation due to rainfall for a LOS path operating at 50 GHz and located in central Australia. The path length is 20 km and the desired time availability is 99.99%. Assume vertical polarization.
13 Calculate the excess attenuation due to rainfall for a LOS path 25 km long with an operating frequency of 18 GHz and for which the desired path availability (propagation reliability) is 99.99%. The path is located in the state of Massachusetts.
14 Name five ways to build a rainfall margin for the path in question 13.
15 Calculate the excess attenuation due to rainfall for a satellite path with a 20° elevation angle for a 21-GHz downlink. The earth station is located in southern Minnesota and the desired time availability for the link is 99%.
16 An earth station is to be located near Boon, Germany, and will operate at 14 GHz. The desired uplink time availability is 99.95% and the subsatellite point is 10° W. What is the excess attenuation due to rainfall?
17 An earth station is to be installed in Diego Garcia with an uplink at 44 GHz. The elevation angle is 15° and the desired path (time) availability is 99%. What value of excess attenuation due to rainfall should be used in the link budget?
18 There is an uplink at 30 GHz and the required excess attenuation due to rainfall is 15 dB. Path diversity is planned. Show how the value of excess attenuation due to rainfall for a single site can be reduced for site separations of 1, 2, 4, and 8 km.
19 For an earth station, calculate the excess attenuation due to atmospheric gases for a site near sea level. The site is planned for 30/20-GHz operation. The elevation angle is 15°. The relative humidity is 60% and the surface temperature is 70°F.
20 Calculate the sky noise contribution for the attenuation of gases calculated in question 19. Calculate the sky noise temperature due to the excess attenuation due to rainfall from question 17.
21 Why do so many satellite communication standards set minimum elevation angles for ''guaranteed'' performance? For example, below 10 GHz, 5°; between 10 and 20 GHz, 10°; and often above 20 GHz, 15°.
22 Name the principal cause of depolarization on satellite links. Name at least two other causes.
23 What are the principal causes and effects of scintillation on satellite links?
24 What is the main drawback in building very large aperture antennas for the higher frequencies? Consider what happens as both aperture size and frequency increase.
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