Do we need Tuning components between Balun and Chip Antenna for nRF51822-QFA ?

[Anil_Anehas]

Hi,

For a new design with nRF51822-QFA, planning to use Johanson Balun and Chip antenna as shown in attached diagram. Not using any tuning components between Balun and Chip antenna since both are 50 ohm and planning to use an impedance controlled trace between Balun and Chip Antenna.

Question is Do we really need tuning components between Balun and Chip Antenna ?

If yes, please suggest the configuration and values ( an example schematic would be really helpful )

Thanks, Anil

[RK]

You really need it if you want to really get a proper match and full range, yes. Because although the balun is designed to have 50 ohms exact output, the antenna is designed to be exactly 50 ohms input and your trace is sized to be 50 ohms, the balun is going to be pretty close, your trace could be a little off because .. it could and the actual impedence of the chip antenna is going to be dependent on placement and what's around it on the board and whether it's near your hand or in a case or anything else. So the actual impedence of the antenna is probably not going to be 50 ohms.

So yes you need the pi network.

If you use the search feature you'll find lots of links to discussions about pi networks, with diagrams and many of them will point you to the antenna tuning document(s) which Nordic publishes, which also has diagrams in it.

[Anil_Anehas]

Thanks RK. Will add a pi network