ST25R3911B matching impedance target In the app note an4974, ST recommends a matching impedance of around 16-20 Ohms, this part is reasonable and makes complete sense. In my configuration, I'm using differential with AAT. According to the app note, the target impedance should be at the bottom of the loop, near the real axis (again, this part makes sense) but it is not at the point closest to the real axis (which has the minimum imaginary component). I have seen various matching recommendations, mostly with the loop either centered about the real axis, or the loop below the real axis and the match point at the point at the left most crossing of the real axis. This is because as you present a tag, the match point will shift clockwise. If you're at the center of the loop, then that shift will reduce your impedance. If the loop is below the real axis and you've matched at the left crossing, then a clockwise shift will increase your impedance as you move a card closer to the antenna. Why does ST recommend putting the loop ABOV
