Question E9B03:
What is the front-to-side ratio of the antenna radiation pattern shown in Figure E9-1?  

Choices:  
A: 12 dB  
B: 24 dB  
C: 18 dB  
D: 14 dB    

Correct Answer is  D: 14 dB  

To find front-to-side ratio, read the gain in the forward (0°) direction and subtract the gain at 90° (side) from the polar plot.

1) Why 14 dB is correct
- From Figure E9-1, the main lobe (front) reads about +8 dB and the side (90°) reads about −6 dB.
- Compute the ratio in dB:
  $$F/S_{\text{dB}} = G_{\text{front}} - G_{\text{side}} = 8 - (-6) = 14\ \text{dB}$$
- Equivalent interpretation (if the plot is normalized to the max at 0 dB): front = 0 dB, side ≈ −14 dB, so the difference is still 14 dB.

2) Why the other choices are incorrect
- 12 dB: Would require a side level of −4 dB (with front at +8 dB) or a front of +6 dB (with side at −6 dB), which does not match the figure.
- 18 dB: Would require the side to be around −10 dB (with front at +8 dB), not what the plot shows.
- 24 dB: Far larger than indicated; would imply the side is about −16 dB relative to a +8 dB front, not supported by the plot.

3) Useful formulas and tips
- Front-to-side ratio (in dB):
  $$F/S_{\text{dB}} = G_{\text{front(dB)}} - G_{\text{side(dB)}}$$
- Converting dB to linear power ratio:
  $$\text{Power ratio} = 10^{\left(\frac{\text{dB}}{10}\right)}$$
  For 14 dB:
  $$10^{1.4} \approx 25:1$$
- Rule of thumb: 3 dB ≈ 2× power, 10 dB = 10× power.