Match transmission structures to their typical propagation modes: (A) Stripline, (B) Hollow rectangular waveguide, (C) Microstrip, (D) Corrugated waveguide.

Introduction / Context:
Microwave structures support different field configurations. Recognizing whether a line supports pure TEM, quasi-TEM, TE/TM, or hybrid modes is crucial for impedance control, dispersion, and loss calculations in RF design.

Given Data / Assumptions:

• Stripline: homogeneous dielectric environment between ground planes.
• Hollow rectangular waveguide: air-filled metallic duct.
• Microstrip: inhomogeneous (air + substrate) planar line.
• Corrugated waveguide: ridged/corrugated interior for mode control (e.g., HE11).

Concept / Approach:
Pure TEM requires a simply connected, homogeneous medium (stripline). In hollow waveguides, true TEM cannot propagate; instead, TE/TM modes exist. Microstrip supports quasi-TEM due to field fringing into air. Corrugations create hybrid modes with desirable dispersion and low cross-polarization.

Step-by-Step Solution:

Verification / Alternative check:
Field solutions show microstrip's effective dielectric constant < substrate permittivity because some energy is in air; rectangular guides have cut-off for dominant TE10; stripline’s symmetry supports TEM at all frequencies until dispersion from dielectric losses/width becomes relevant.

Why Other Options Are Wrong:

• A-2, B-1, C-3, D-4: Claims waveguide supports quasi-TEM—incorrect.
• A-4, B-1, C-3, D-2: Misplaces hybrid/quasi-TEM assignments.
• A-4, B-3, C-1, D-2: Assigns hybrid to stripline and microstrip to TE/TM.

Common Pitfalls:

• Assuming microstrip is pure TEM; it is only quasi-TEM.
• Forgetting that hollow metallic waveguides cannot support TEM without a center conductor.

Final Answer:
A-2, B-3, C-1, D-4