# Pdoa result varies along z-axis

Hi everyone:
i am testing my pdoa devboard with DW3220 using the example simple_rx_pdoa/simple_tx_pdoa. I found that the result is ok when the node and tag are In the same horizontal plane. However, for examle, when i fix the tag in the 0° direction and move it up and down, the results vary greatly, up to 30°~90°.

Anybody know why? Or how to solve it? Thanks a lot.

The Mona Lisa (ML) antenna has 2 antenna elements which are spaced apart to be able to receive a phase difference in the horizontal plane given the current orientation of the ML antenna from your picture. If you now move your tag in the vertical plane, there will not be much of a phase difference (or unknown phase difference) leading to random AoA values.

As an exercise, you can rotate your ML antenna by 90 degrees and then it should work fine in the vertical plane but not in the horizontal plane.

If you want to measure AoA in both the horizontal and vertical (or azimuth and elevation), you will need 3 antenna elements.

No phase difference should give a value of 0 not a random number.

He’s not expecting an elevation angle measurement, just a stable 0 value for the heading.

As for why, I have no idea. It looks semi-consistent (negative angles for down, positive for up) that implies it is a physical antenna effect rather than just random numbers. But as to what is causing that effect I have no idea.

True that no phase difference will give a value of 0 but given that he is using his hand to move the tag up and down, I’m guessing it is not perfectly perpendicular to the ML antenna. Also, his hand may be slightly hedging to the right when moving up and slightly hedging to the left when moving down. (Just a thought)

Thank you for your reply. You’re right. I moved the tag up and down right in front of the antenna, aspecting a stable result around 0°.

Thank you for your reply. Ture that my hand maybe moved slghtly left and right, so changes from -10°~10° is ok. But the question is the result varies greatly, up to 30°. It’s obviously not because of my hands.