Page 414 - Satellite Communications, Fourth Edition

394 Chapter Twelve

12.4. Calculate the gain in decibels and the effective area of a 30-m parabolic
antenna at a frequency of 4 GHz.

12.5. An antenna has a gain of 46 dB at 12 GHz. Calculate its effective area.

12.6. Calculate the effective area of a 10-ft parabolic reflector antenna at a
frequency of (a) 4 GHz; (b) 12 GHz.

12.7. The EIRP from a satellite is 49.4 dBW. Calculate (a) the power density
at a ground station for which the range is 40,000 km and (b) the power delivered
to a matched load at the ground station receiver if the antenna gain is 50 dB.
The downlink frequency is 4 GHz.

12.8. Calculate the free-space loss as a power ratio and in decibels for
transmission at frequencies of (a) 4 GHz, (b) 6 GHz, (c) 12 GHz, and (d) 14
GHz; the range being 42,000 km.
12.9. Repeat the calculation in Prob. 12.7b allowing for a fading margin of 1.0
dB and receiver feeder losses of 0.5 dB.
12.10. Explain what is meant by (a) antenna noise temperature, (b) amplifier
noise temperature,and (c) system noise temperature referred to input. A system
operates with an antenna noise temperature of 40 K and an input amplifier noise
temperature of 120 K. Calculate the available noise power density of the system
referred to the amplifier input.

12.11. Two amplifiers are connected in cascade, each having a gain of 10 dB
and a noise temperature of 200 K. Calculate (a) the overall gain and (b) the
effective noise temperature referred to input.
12.12. Explain what is meant by noise factor. For what source temperature is
noise factor defined?
12.13. The noise factor of an amplifier is 7:1. Calculate (a) the noise figure and
(b) the equivalent noise temperature.
12.14. An attenuator has an attenuation of 6 dB. Calculate (a) its noise figure
and (b) its equivalent noise temperature referred to input.

12.15. An amplifier having a noise temperature of 200 K has a 4-dB attenuator
connected at its input. Calculate the effective noise temperature referred to the
attenuator input.

12.16. A receiving system consists of an antenna having a noise temperature
of 60 K, feeding directly into a LNA. The amplifier has a noise temperature of
120 K and a gain of 45 dB. The coaxial feeder between the LNA and the main
receiver has a loss of 2 dB, and the main receiver has a noise figure of 9 dB.
Calculate the system noise temperature referred to input.