Question
What is the front-to-back ratio of the radiation pattern shown in Figure E9-2?
Answer Options
- A) 15 dB
- B) 28 dB
- C) 3 dB
- D) 38 dB
Correct Answer: B
Explanation
The front-to-back (F/B) ratio measures the difference between the peak signal power in the main direction and the signal power in the exact opposite direction (180°). Figure E9-2 displays an elevation pattern (vertical angle) for an antenna, where the front direction is the peak of the main lobe (at 7.5° elevation) and the back direction is 180° along the azimuth, which is often referenced as the null directly into the ground (90° or 180° on the hemisphere in this diagram, or sometimes the lobe closest to 180° if looking at the horizontal pattern).
Assuming the F/B ratio for this elevation cut is defined by the difference between the main lobe and the largest rear lobe (at approximately 180° on the diagram’s axis, which is the ground level reflection point on this cut): Assuming the pattern’s reference appears normalized, as the forward gain is 0 dB. The signal at 180° is -28 dB. The difference is 28 dB. (This high F/B ratio indicates excellent rejection of signals arriving from the rear hemisphere.)
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