What is the difference in radiated power between a lossless antenna with gain and an isotropic radiator driven by the same power?
The correct answer is C: They are the same. The difference in radiated power between a lossless antenna with gain and an isotropic radiator driven by the same power is that they are the same. Both antennas radiate the same total power; the gain antenna just concentrates it in certain directions.
Antenna gain doesn't create power - it redistributes it. A lossless antenna with gain takes the same input power and focuses it in certain directions, making those directions stronger. But the total radiated power equals the input power (for a lossless antenna). An isotropic radiator radiates equally in all directions. Both radiate the same total power; the gain antenna just has more power in some directions and less in others. Gain is about directionality, not total power.
Exam Tip
Gain antenna vs isotropic = Same total power. Remember: A lossless antenna with gain and an isotropic radiator driven by the same power radiate the same total power. Gain redistributes power directionally but doesn't create it.
Memory Aid
"**G**ain **A**ntenna **P**ower = **I**sotropic **P**ower (think 'GAP = IP', same total power)"
Real-World Application
You drive a lossless Yagi (with gain) and an isotropic radiator with 100 watts each. Both radiate 100 watts total. The Yagi concentrates power in its forward direction (maybe 10× stronger forward), but the total radiated power is still 100 watts. The isotropic radiates equally in all directions. Gain is about directionality, not total power.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. The power radiated isn't increased by gain. Gain redistributes power directionally, but total radiated power equals input power for lossless antennas.
Option B: Incorrect. Front-to-back ratio is about directionality, not total radiated power. Both antennas radiate the same total power.
Option D: Incorrect. The isotropic radiator doesn't radiate more power. Both antennas radiate the same total power when driven by the same input power.
题目解析
The correct answer is C: They are the same. The difference in radiated power between a lossless antenna with gain and an isotropic radiator driven by the same power is that they are the same. Both antennas radiate the same total power; the gain antenna just concentrates it in certain directions. Antenna gain doesn't create power - it redistributes it. A lossless antenna with gain takes the same input power and focuses it in certain directions, making those directions stronger. But the total radiated power equals the input power (for a lossless antenna). An isotropic radiator radiates equally in all directions. Both radiate the same total power; the gain antenna just has more power in some directions and less in others. Gain is about directionality, not total power.
考试技巧
Gain antenna vs isotropic = Same total power. Remember: A lossless antenna with gain and an isotropic radiator driven by the same power radiate the same total power. Gain redistributes power directionally but doesn't create it.
记忆口诀
**G**ain **A**ntenna **P**ower = **I**sotropic **P**ower (think 'GAP = IP', same total power)
实际应用示例
You drive a lossless Yagi (with gain) and an isotropic radiator with 100 watts each. Both radiate 100 watts total. The Yagi concentrates power in its forward direction (maybe 10× stronger forward), but the total radiated power is still 100 watts. The isotropic radiates equally in all directions. Gain is about directionality, not total power.
错误选项分析
Option A: Incorrect. The power radiated isn't increased by gain. Gain redistributes power directionally, but total radiated power equals input power for lossless antennas. Option B: Incorrect. Front-to-back ratio is about directionality, not total radiated power. Both antennas radiate the same total power. Option D: Incorrect. The isotropic radiator doesn't radiate more power. Both antennas radiate the same total power when driven by the same input power.
知识点
Antenna gain, Radiated power, Isotropic radiator, Power conservation
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.