What matching system uses a short length of transmission line connected in parallel with the feed line at or near the feed point?
The correct answer is D: Stub match. A stub match is a matching system that uses a short length of transmission line connected in parallel with the feed line at or near the feed point. The stub provides reactance to cancel the antenna's reactive component.
A stub match uses a short section of transmission line (open or shorted at the far end) connected in parallel with the main feed line. The stub's length and termination (open or short) are chosen to provide the right reactance to cancel the antenna's reactance, making the impedance purely resistive and matched. Stub matches are commonly used because they're simple and effective. They can be made from the same transmission line as the feed line, making them convenient. The stub is typically 1/4 wavelength or less.
Exam Tip
Stub match = Parallel transmission line. Remember: A stub match uses a short length of transmission line connected in parallel with the feed line at or near the feed point to provide matching reactance.
Memory Aid
"**S**tub **M**atch = **P**arallel **T**ransmission **L**ine (think 'SM = PTL')"
Real-World Application
You're matching an antenna using a stub match. You connect a short piece of transmission line (maybe 1/4 wavelength) in parallel with your feed line at the antenna feed point. The stub is open or shorted at the far end. The stub's reactance cancels the antenna's reactance, matching the impedance. This is a simple and effective matching method.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Gamma match uses a series connection with an offset point, not a parallel stub.
Option B: Incorrect. Delta match uses a different configuration, not a parallel stub.
Option C: Incorrect. T-match uses connections at different points, not a parallel stub configuration.
题目解析
The correct answer is D: Stub match. A stub match is a matching system that uses a short length of transmission line connected in parallel with the feed line at or near the feed point. The stub provides reactance to cancel the antenna's reactive component. A stub match uses a short section of transmission line (open or shorted at the far end) connected in parallel with the main feed line. The stub's length and termination (open or short) are chosen to provide the right reactance to cancel the antenna's reactance, making the impedance purely resistive and matched. Stub matches are commonly used because they're simple and effective. They can be made from the same transmission line as the feed line, making them convenient. The stub is typically 1/4 wavelength or less.
考试技巧
Stub match = Parallel transmission line. Remember: A stub match uses a short length of transmission line connected in parallel with the feed line at or near the feed point to provide matching reactance.
记忆口诀
**S**tub **M**atch = **P**arallel **T**ransmission **L**ine (think 'SM = PTL')
实际应用示例
You're matching an antenna using a stub match. You connect a short piece of transmission line (maybe 1/4 wavelength) in parallel with your feed line at the antenna feed point. The stub is open or shorted at the far end. The stub's reactance cancels the antenna's reactance, matching the impedance. This is a simple and effective matching method.
错误选项分析
Option A: Incorrect. Gamma match uses a series connection with an offset point, not a parallel stub. Option B: Incorrect. Delta match uses a different configuration, not a parallel stub. Option C: Incorrect. T-match uses connections at different points, not a parallel stub configuration.
知识点
Stub match, Transmission line, Parallel connection, Impedance matching
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.