For the lobe width, which of the following description is correct? (Multiple choice)

Question

Options

• AWithin the range of the main lobe, the angle at which the power density drops by half (3dB) relative
• BThe narrower the beam width, the better the directivity, the farther the radiation distance, and the
• CPatterns usually have two or more lobes
• DThe terminal can receive the signal only within the coverage of the half-power angle

• A
  83% (25)
• D
  17% (5)

Explanation

A correctly defines the half-power beamwidth (HPBW): the angular width within the main lobe where the radiated power density falls to 50% (-3 dB) of its peak value - this is the standard technical definition of beam width. B is correct because concentrating energy into a narrower beam increases directivity (gain), which extends effective range in that direction - the trade-off being reduced angular coverage. C is correct because practical antenna radiation patterns almost always exhibit a main lobe plus at least one or more side lobes and/or a back lobe, making "two or more lobes" the norm.

D is wrong because it overstates the restriction: terminals can receive signals outside the half-power angle - signal strength simply degrades gradually. The half-power boundary is a performance threshold, not a hard coverage cutoff.

Memory tip: Think of a flashlight beam - the bright center is your main lobe (A), a tighter beam shines farther (B), and you always see some spill-light around the edges forming extra "lobes" (C). But you don't go blind the moment you step outside the bright center - just like D is wrong, coverage doesn't abruptly end at the 3 dB boundary.

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