R
Member
Our lab doesn't have a full anechoic chamber — just a small shielded room with absorbers on the walls. Measuring antenna gain there means fighting ripple. Here's what actually helped:
1. Understand where the ripple comes from. In a compact setup the dominant error is multipath: the direct wave interferes with reflections off the chamber walls. The ripple period in frequency tells you the path-length difference, which tells you which wall is guilty.
2. Time gating is your best friend. On the VNA, gate out the late-arriving reflections. You need enough bandwidth for decent time resolution — a good rule of thumb is that your frequency span sets how close two paths you can separate.
3. Reference antenna calibration. Use a known standard-gain horn and do a substitution measurement. This cancels most of the systematic setup errors, as long as you don't move anything between the reference and DUT measurements.
4. Keep the geometry identical. Mark the positioner, the tripod, even the cable routing. Moving a cable by a few centimeters can shift a null by tenths of a dB at higher frequencies.
5. Average, but average smartly. Frequency stirring (slight position offsets across sweeps) beats naive trace averaging when the error is deterministic multipath rather than noise.
With these steps I routinely get within ±0.5 dB of the datasheet gain in our little room — good enough for engineering decisions.
How do you handle gain measurements without a proper chamber? Curious what tricks others use.
1. Understand where the ripple comes from. In a compact setup the dominant error is multipath: the direct wave interferes with reflections off the chamber walls. The ripple period in frequency tells you the path-length difference, which tells you which wall is guilty.
2. Time gating is your best friend. On the VNA, gate out the late-arriving reflections. You need enough bandwidth for decent time resolution — a good rule of thumb is that your frequency span sets how close two paths you can separate.
3. Reference antenna calibration. Use a known standard-gain horn and do a substitution measurement. This cancels most of the systematic setup errors, as long as you don't move anything between the reference and DUT measurements.
4. Keep the geometry identical. Mark the positioner, the tripod, even the cable routing. Moving a cable by a few centimeters can shift a null by tenths of a dB at higher frequencies.
5. Average, but average smartly. Frequency stirring (slight position offsets across sweeps) beats naive trace averaging when the error is deterministic multipath rather than noise.
With these steps I routinely get within ±0.5 dB of the datasheet gain in our little room — good enough for engineering decisions.
How do you handle gain measurements without a proper chamber? Curious what tricks others use.