What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?
The correct answer is A: Cardioid. Two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase create a cardioid (heart-shaped) pattern. This is a unidirectional pattern with a single main lobe and a null in the opposite direction.
The combination of 1/4-wavelength spacing and 90-degree phase difference creates the cardioid pattern. The phase difference and spacing cause the signals to add in one direction and cancel in the opposite direction, creating the characteristic heart-shaped pattern. Cardioid patterns are useful for direction-finding and reducing interference from the rear. This is a common configuration for creating unidirectional patterns from simple arrays.
Exam Tip
1/4λ spacing, 90° phase = Cardioid. Remember: Two 1/4λ verticals, 1/4λ apart, 90° out of phase create a cardioid (heart-shaped) pattern - unidirectional with a rear null.
Memory Aid
"**1**/**4**λ, **9**0° = **C**ardioid (think '1/4λ,90° = C')"
Real-World Application
You set up two 1/4-wave verticals 1/4 wavelength apart and feed them 90 degrees out of phase. The antennas create a cardioid pattern - strong in one direction with a null behind. This is useful for direction-finding because the null gives you a clear indication of direction.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. A figure-eight end-fire would require different spacing or phase. The 1/4-wavelength spacing with 90-degree phase creates a cardioid, not a figure-eight.
Option C: Incorrect. A figure-eight broadside would occur with in-phase feeding and different spacing. The cardioid pattern is unidirectional, not bidirectional.
Option D: Incorrect. The pattern isn't omnidirectional. The 90-degree phase difference creates a directional cardioid pattern.
题目解析
The correct answer is A: Cardioid. Two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase create a cardioid (heart-shaped) pattern. This is a unidirectional pattern with a single main lobe and a null in the opposite direction. The combination of 1/4-wavelength spacing and 90-degree phase difference creates the cardioid pattern. The phase difference and spacing cause the signals to add in one direction and cancel in the opposite direction, creating the characteristic heart-shaped pattern. Cardioid patterns are useful for direction-finding and reducing interference from the rear. This is a common configuration for creating unidirectional patterns from simple arrays.
考试技巧
1/4λ spacing, 90° phase = Cardioid. Remember: Two 1/4λ verticals, 1/4λ apart, 90° out of phase create a cardioid (heart-shaped) pattern - unidirectional with a rear null.
记忆口诀
**1**/**4**λ, **9**0° = **C**ardioid (think '1/4λ,90° = C')
实际应用示例
You set up two 1/4-wave verticals 1/4 wavelength apart and feed them 90 degrees out of phase. The antennas create a cardioid pattern - strong in one direction with a null behind. This is useful for direction-finding because the null gives you a clear indication of direction.
错误选项分析
Option B: Incorrect. A figure-eight end-fire would require different spacing or phase. The 1/4-wavelength spacing with 90-degree phase creates a cardioid, not a figure-eight. Option C: Incorrect. A figure-eight broadside would occur with in-phase feeding and different spacing. The cardioid pattern is unidirectional, not bidirectional. Option D: Incorrect. The pattern isn't omnidirectional. The 90-degree phase difference creates a directional cardioid pattern.
知识点
Cardioid pattern, Antenna array, 90 degrees out of phase, Unidirectional pattern
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.