QUESTION 17 What is correct regarding an ideal isotropic antenna? a. An ideal isotropic antenna is a highly efficient antenna used extensively in today's communication systems b. An ideal isotropic antenna is a specialized antenna used to direct EM signal energy towards a specific direction c An ideal isotropic antenna is a theoretical antenna that does not exist in practice, but is useful in explaining power density and unguided EM signal attenuation d. None of the above are correct statements QUESTION 18 Select the correct statement(s) regarding optical signals a. Optical signals are immune from radio frequency interference (RFI) b. Optical signal operate in the THz frequency range, which can support high data throughput. o c. Optical signals cannot be collected using RF antennas. d. All are correct statements