Match antennas to their typical directivity levels: (A) Horn antenna, (B) Parabolic antenna, (C) Lens antenna — with: (1) high directivity, (2) very high directivity, (3) moderate directivity.
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AA-1, B-2, C-3
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BA-3, B-2, C-1
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CA-3, B-1, C-2
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DA-1, B-3, C-2
Answer
Correct Answer: A-3, B-2, C-1
Explanation
Introduction / Context:Antenna directivity measures how concentrated the radiated power is in a particular direction. Recognizing typical directivity ranges for common microwave antennas is essential in RF system design.
Given Data / Assumptions:
- Antennas: Horn, Parabolic reflector, Dielectric lens.
- Directivity labels: moderate, high, very high.
Concept / Approach:A horn provides aperture matching and moderate gain; a parabolic reflector focuses energy tightly for very high directivity; a lens antenna increases directivity by phase-front shaping, generally between horn and large parabolic dishes.
Step-by-Step Solution:
Horn → moderate directivity (often tens of dBi when large, but typically below equivalent large dishes) → 3.Parabolic → very high directivity due to large effective aperture and precise focusing → 2.Lens → high directivity (improves collimation beyond horns without reflectors) → 1.Verification / Alternative check:Rule of thumb: Directivity ∝ effective aperture area. Parabolic reflectors typically achieve the highest for a given size; horns are simpler waveguide flares; lenses add focusing power without reflectors.
Why Other Options Are Wrong:
- A-1, B-2, C-3: Overstates horn and understates lens relative positions.
- A-3, B-1, C-2: Swaps lens and parabolic levels.
- A-1, B-3, C-2: Misorders all three against typical practice.
Common Pitfalls:
- Equating gain one-for-one with size without considering aperture efficiency.
- Assuming horns inherently provide very high directivity regardless of dimensions.
Final Answer:A-3, B-2, C-1