The lobe width is a very important parameter commonly used in directional antennas. It refers to the width of the angle formed by the radiation pattern of the antenna below the peak value () dB.

Question

Options

• A3
• B4
• C5
• D6

• A
  76% (19)
• B
  12% (3)
• C
  8% (2)
• D
  4% (1)

Explanation

Option A is correct because lobe width - also called beamwidth or half-power beamwidth (HPBW) - is universally defined as the angular width of the main radiation lobe measured at the points where the radiated power drops to half of its peak value, and half-power corresponds exactly to a 3 dB reduction below the peak. This is a foundational standard in antenna engineering used across specifications, datasheets, and IEEE definitions. Options B (4 dB), C (5 dB), and D (6 dB) are wrong because no standard definition of lobe width uses those thresholds - they are distractors exploiting the fact that multiple dB values appear in antenna specifications, but none mark the half-power point. The half-power point is special because it is the natural boundary where the beam's useful energy begins to fall off significantly.

Memory tip: Recall that "half power = 3 dB" is a fixed relationship in logarithmic math - 10 x log10(0.5) equals approximately -3 dB. Lobe width is always measured at the half-power (3 dB) points, so if you remember that formula, option A locks in immediately.

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