In radio propagation terminology, a space wave can consist of which component paths?

Introduction / Context:
Space-wave propagation dominates in VHF, UHF, and microwave links. Understanding what constitutes the space wave clarifies link budgets, fading mechanisms, and path profiles used in terrestrial and line-of-sight systems such as TV broadcast and point-to-point microwave links.

Given Data / Assumptions:

• Space wave refers to near-line-of-sight propagation not dependent on ionospheric reflection.
• Possible components include direct and ground-reflected rays.

Concept / Approach:

The space wave typically includes the direct LOS component and a ground-reflected component (forming a two-ray model). At higher frequencies, diffraction around obstacles and tropospheric refraction/scatter may also contribute, but the classical definition emphasizes LOS and Earth-reflected rays, excluding ionospheric reflection (sky wave).

Step-by-Step Solution:

Verification / Alternative check:

Two-ray propagation models used in microwave engineering explicitly consider the direct and ground-reflected components of the space wave to predict fading/notching.

Why Other Options Are Wrong:

• Only direct or only reflected: incomplete definitions.
• Ionospheric (sky) wave and troposcatter alone are different mechanisms, not the basic space wave.

Common Pitfalls:

Confusing sky-wave propagation (HF) with space-wave (VHF+). Space wave is primarily LOS and ground-reflection based.

Final Answer:

Direct wave or the wave reflected from the Earth's surface (or both)