* Question
How to measure the angular sensitivity (read performance) of an RFID tag relative to the reader antenna?
* Answer
Use a low-reflection environment, fix the tag–antenna distance and test band, keep the reader settings constant, and slowly rotate the tag (azimuth first; add elevation if needed). At each angle, log whether the tag can be read stably and record either the minimum transmit power required or the maximum readable distance. Plot the results as a polar chart—peaks mark “good” angles, dips mark “poor” angles.
Why measure it?
Different orientations change the coupling and polarization match between the tag and the reader antenna. Read performance can differ by several dB, directly affecting range and stability.
What to record (pick one or both):
Minimum transmit power for a stable read: The lowest power that still reads reliably at that angle (lower is better).
Maximum read range: At fixed transmit power, the farthest distance that still reads at that angle (farther is better).
How to do it (five quick steps):
Choose an open or anechoic space and fix the distance between tag and antenna (e.g., 2 m).
Set the reader’s power and frequency band (e.g., 915 MHz) and keep all settings unchanged.
Rotate the tag in angle steps (e.g., every 5°) and note whether reads are stable.
Use one method:
Power method: At that angle, step the transmit power down to find the lowest level that still reads reliably.
Distance method: Keep power fixed and move the tag outward/inward to find the farthest readable distance.
Compile all angles into a polar plot or heat map to visualize the best and worst directions at a glance.
Tips:
Match polarization: Mismatched polarization between reader and tag can create deep nulls; missing reads there is normal.
Prefer far field: Very short distances can distort results; measure in the far field for realism.
Test on real materials: Mounting the tag on metal, plastic, or liquid containers changes performance—test each case separately.
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