Microwaves and the ionosphere — typical behavior How do microwave-frequency signals interact with the Earth’s ionosphere under normal conditions?

Introduction / Context:
The ionosphere significantly affects HF and some VHF communications by refracting or reflecting radio waves back to Earth. However, the behavior at microwave frequencies is very different. Understanding this is vital for satellite links, radar, and terrestrial microwave relays.

Given Data / Assumptions:

• Frequency regime: microwaves (approximately > 1 GHz).
• Typical mid-latitude ionospheric electron densities and collision rates.
• Normal propagation conditions (no extreme events).

Concept / Approach:
The ionosphere's refractive index depends on plasma frequency f_p, which scales with electron density. For reflection to occur, the radio frequency f must be less than or comparable to f_p. Microwave frequencies are far above typical ionospheric plasma frequencies, so they pass through with little refraction and minimal absorption. This is why satellite communications (GHz bands) operate reliably through the ionosphere, suffering mainly from tropospheric, not ionospheric, effects.

Step-by-Step Solution:

Verification / Alternative check:
Satellite downlinks (e.g., L-, S-, X-, Ku-, Ka-bands) demonstrate negligible ionospheric reflection/absorption compared to lower-frequency HF skywave behavior.

Why Other Options Are Wrong:

• Reflected: true for HF/VHF under certain conditions, not for microwaves.
• Absorbed: ionospheric absorption at GHz is minor.
• Both reflected and absorbed: contradicts plasma-frequency scaling.

Common Pitfalls:
Generalizing HF skywave concepts to microwaves; ignoring that troposphere, rain, and clouds dominate microwave propagation impairments (e.g., rain fade).

Final Answer:
are neither reflected nor absorbed by ionosphere