Explanation: Measuring VSWR (Voltage Standing Wave Ratio) at microwave frequencies often requires specialized equipment due to the high frequencies involved. A **network analyzer** (specifically a Vector Network Analyzer or VNA) is an ideal tool. It directly measures S-parameters, including the reflection coefficient (S11 or S22), from which VSWR is easily calculated across a wide frequency range with high accuracy. Alternatively, VSWR can be determined by measuring the forward and reflected power. A **dual directional coupler** samples both the forward and reflected power in the transmission line. These sampled powers are then measured using a **power meter** (or two, one for each direction). The ratio of reflected to forward power allows calculation of VSWR. Therefore, option D is the most complete and correct answer because it encompasses both primary methods: using a network analyzer for direct S-parameter measurement, or using a dual directional coupler and a power meter to calculate VSWR from measured forward and reflected power. A spectrum analyzer (C) primarily measures power versus frequency and doesn't directly measure VSWR without additional setup, making it less suitable on its own.