An electronic device may include wireless circuitry with a phased antenna array that conveys radio-frequency signals using signal beams of first and second orthogonal polarizations. The array may sweep over a set of signal beam pairs, each including a respective combination of signal beams of the first and second polarizations. The wireless circuitry may gather performance metric values for each of the polarizations and signal beam pairs. The circuitry may generate a filtered set of signal beam pairs by removing signal beam pairs having performance metric values that differ from a maximum of the wireless performance metric values by more than a threshold. The circuitry may select a signal beam pair from the filtered set having a minimum polarization imbalance. The array may concurrently convey first and second wireless data streams using the selected signal beam pair. Minimizing polarization imbalance may maximize overall data throughput for the device.