What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase?
The correct answer is C: A figure-eight broadside to the axis of the array. Two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase create a figure-eight pattern broadside to the axis of the array. The pattern has lobes perpendicular to the line between antennas.
When two antennas are fed in phase with 1/2-wavelength spacing, they reinforce in the broadside direction (perpendicular to the line between them) and cancel along the axis. This creates a figure-eight pattern with the lobes broadside to the array. The in-phase feeding and 1/2-wavelength spacing are key to this pattern. This is different from 180-degree out-of-phase feeding, which creates an end-fire pattern along the axis.
Exam Tip
1/2λ spacing, in phase = Figure-eight broadside. Remember: Two 1/4λ verticals, 1/2λ apart, in phase create a figure-eight pattern broadside to the array axis (perpendicular to the line between antennas).
Memory Aid
"**1**/**2**λ, **I**n **P**hase = **F**igure-**8** **B**roadside (think '1/2λ,IP = F8B')"
Real-World Application
You set up two 1/4-wave verticals 1/2 wavelength apart and feed them in phase. The antennas reinforce in the broadside direction (perpendicular to the line between them) and cancel along the axis, creating a figure-eight pattern with lobes broadside. This is a broadside array pattern.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. The pattern isn't omnidirectional. The in-phase feeding with 1/2-wavelength spacing creates a directional figure-eight pattern.
Option B: Incorrect. A cardioid pattern requires 1/4-wavelength spacing with 90-degree phase, not 1/2-wavelength with in-phase.
Option D: Incorrect. A figure-eight end-fire would occur with 180-degree out-of-phase feeding, not in-phase. In-phase creates a broadside pattern.
题目解析
The correct answer is C: A figure-eight broadside to the axis of the array. Two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase create a figure-eight pattern broadside to the axis of the array. The pattern has lobes perpendicular to the line between antennas. When two antennas are fed in phase with 1/2-wavelength spacing, they reinforce in the broadside direction (perpendicular to the line between them) and cancel along the axis. This creates a figure-eight pattern with the lobes broadside to the array. The in-phase feeding and 1/2-wavelength spacing are key to this pattern. This is different from 180-degree out-of-phase feeding, which creates an end-fire pattern along the axis.
考试技巧
1/2λ spacing, in phase = Figure-eight broadside. Remember: Two 1/4λ verticals, 1/2λ apart, in phase create a figure-eight pattern broadside to the array axis (perpendicular to the line between antennas).
记忆口诀
**1**/**2**λ, **I**n **P**hase = **F**igure-**8** **B**roadside (think '1/2λ,IP = F8B')
实际应用示例
You set up two 1/4-wave verticals 1/2 wavelength apart and feed them in phase. The antennas reinforce in the broadside direction (perpendicular to the line between them) and cancel along the axis, creating a figure-eight pattern with lobes broadside. This is a broadside array pattern.
错误选项分析
Option A: Incorrect. The pattern isn't omnidirectional. The in-phase feeding with 1/2-wavelength spacing creates a directional figure-eight pattern. Option B: Incorrect. A cardioid pattern requires 1/4-wavelength spacing with 90-degree phase, not 1/2-wavelength with in-phase. Option D: Incorrect. A figure-eight end-fire would occur with 180-degree out-of-phase feeding, not in-phase. In-phase creates a broadside pattern.
知识点
Antenna array, In phase, Figure-eight pattern, Broadside array
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.