Assertion–Reason (hollow waveguides at microwave frequencies): Assertion (A): Hollow metallic waveguides are frequently used as transmission lines at microwave frequencies. Reason (R): Waveguides offer high power-handling capability and low loss, making them suitable for long runs and high fields.

Introduction / Context:
Choosing a transmission medium at microwave frequencies involves trade-offs among loss, bandwidth, mechanical complexity, and power handling. Hollow metallic waveguides remain relevant in radar, satellite earth stations, and high-power links because of their low attenuation and ability to withstand strong electric fields without breakdown.

Given Data / Assumptions:

• We are comparing hollow guides with alternatives like coaxial cables and microstrip.
• Frequency range is in the microwave region where waveguides support TE/TM modes above cutoff.
• Practical installations prioritize low loss and high RF power capability.

Concept / Approach:

Waveguides operate in single or few modes with metal walls confining fields. Conductor loss is low because currents distribute over large interior surfaces, and air or low-loss gas minimizes dielectric loss. The large cross section and pressurization options allow high peak and average powers. Thus, the very properties cited in the reason directly explain the widespread use asserted.

Step-by-Step Solution:

Verification / Alternative check:

Empirical attenuation charts show waveguides outperforming coax at high GHz over long distances. Power ratings for waveguides exceed those of comparable coax due to larger breakdown margins, aligning with the reason provided.

Why Other Options Are Wrong:

• Claiming R is not the explanation ignores the direct causality between low loss/high power and adoption.
• Declaring A or R wrong contradicts established microwave practice.

Common Pitfalls:

Equating mechanical simplicity with electrical suitability. While waveguides can be mechanically more involved than coax, electrically they excel for low-loss, high-power tasks, which is the point of the reason.

Final Answer:

Both A and R are correct and R is correct explanation of A