Question
What type of antenna can be used to minimize the effects of spin modulation and Faraday rotation?
Answer Options
- A) A linearly polarized antenna
- B) A circularly polarized antenna
- C) An isotropic antenna
- D) A log-periodic dipole array
Correct Answer: B
Explanation
When a satellite signal travels through space and the ionosphere, its polarization plane can rotate (Faraday rotation), causing deep and irregular fading. Additionally, many satellites rotate on their axis for stabilization, causing the polarization of the onboard antenna to change relative to the ground station (spin modulation). Both effects can cause signals to momentarily drop below the noise floor.
To combat these effects, ground stations typically use a circularly polarized antenna (either right-hand or left-hand circular). This type of antenna is designed to receive signals regardless of the polarization angle, effectively mitigating the fading caused by both Faraday rotation and spin modulation, resulting in a more stable received signal.
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