Question
What is the front-to-back ratio of the antenna radiation pattern shown in Figure E9-1?
Answer Options
- A) 36 dB
- B) 14 dB
- C) 24 dB
- D) 18 dB
Correct Answer: D
Explanation
The front-to-back (F/B) ratio of a directional antenna (like the one shown in Figure E9-1) is the measure of how much stronger the signal is radiated in the main lobe direction (0°) compared to the signal radiated in the exact opposite direction (180°). This is a critical factor for rejecting interference from behind the antenna.
Referring to Figure E9-1, the maximum (peak) gain is at 0°, where the reading is 0 dB (the reference level). The signal in the reverse direction (180°) has an amplitude of approximately -18 dB. The F/B ratio is the difference between these two: 0 dB - (-18 dB) = 18 dB. A higher F/B ratio indicates better unwanted signal rejection from the rear.
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