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Using a VNA to Measure a Small Magnetic Loop

In addition to size, weight, and tunability, the efficiency of a magnetic loop antenna is an important performance metric. This article shows how the efficiency can be estimated using VNA measurements, even when a feed cable is present and the matching is not ideal.

Equivalent circuit with transformer for the small magnetic loop measurement setup.

Smith chart: The measured values do not reach the outer circle, which indicates cable attenuation. The circle also does not pass through the chart center, so the antenna is not matched to SWR 1.0.

You can read the full article as a PDF here: measure_a_magnetic_loop.pdf.