Assertion (A): A slotted line is frequently used for microwave measurements such as VSWR, guided wavelength, reflection coefficient, and load impedance extraction. Reason (R): The unknown load impedance is mounted at the end of the slotted line so that a measurable standing wave pattern is created along the slot for probing.

Introduction / Context:
Before vector network analyzers became commonplace, the slotted line was a primary instrument for characterizing microwave components. It consists of a precision transmission line with a longitudinal slot and a movable probe that samples the electric field to trace the standing wave pattern. This question tests recognition of what a slotted line measures and why it is useful.

Given Data / Assumptions:

• A low loss transmission line section with a slot and a calibrated carriage for the detector probe.
• The unknown device under test is mounted at the end of the slotted section.
• Power levels are low enough that probe loading is negligible for measurement accuracy.

Concept / Approach:

The slotted line allows direct measurement of voltage maxima and minima and their spacing. From these, one calculates guided wavelength, standing wave ratio, the magnitude and angle of the reflection coefficient, and ultimately the load impedance using known relationships with the characteristic impedance. These capabilities explain why the slotted line is frequently used in classical microwave laboratories.

Step-by-Step Solution:

Verification / Alternative check:

Smith chart reconstruction using the measured reflection magnitude and phase yields the same load impedance as the algebraic method, providing a cross check for the slotted line results.

Why Other Options Are Wrong:

• If R were the full explanation for A, it would need to mention the wide set of quantities that the slotted line can measure. R is accurate but only describes the setup, not the comprehensive reason for frequent use.
• Any option denying A or R contradicts standard microwave measurement practice over many decades.

Common Pitfalls:

Ignoring probe coupling errors, neglecting line losses that reduce the contrast of minima and maxima, and confusing free space wavelength with guided wavelength when interpreting spacing. Careful calibration and probe positioning are crucial for accuracy.

Final Answer:

Both A and R are correct but R is not correct explanation of A