Advice on antenna tuning ?

[RobK1]

I am currently working to redesign one of our products to include Bluetooth communication for remote control. For this, I am targetting the STM32WBA23.

Given that the PCB is mounted inside a solid, cast-aluminium housing, I will need to put the antenna on a seperate board and connect it with a cable to the main PCB.

My question now is: Where do I put the tuning components? Do I place these on the main PCB, close to the controller, or do I put them on the antenna board?
Or maybe it doesn't actually matter.

I would appreciate any comments and directions by those more RF savvy than me.

[Imen.D]

Hello @RobK1 ,

Please have a look at the following application notes that may help you on your design :

• AN5434: Guidelines for on-board antenna reference designs for STM32WB/WBA MCUs
• AN5948 How to develop RF hardware using STM32WBA MCUs 

[RobK1]

Hi @Imen.D ,

Thanks for your reply. I had already seen the first app.note (correct link: Guidelines for on-board antenna reference designs for STM32WB/WBA MCUs - Application note), the second was new to me.
Both, unfortunately do not (directly) answer my question of where to put the matching circuit, whether three- or five element, with or without IPD.

My best guess is to place them on the auxilary board, close to the antenna. Given that the RF pin of the MCU wants to see 50 Ohms, I can route a CPW(G) to a U.FL connector on the main board. Cable to the aux. board -> matching circuit -> antenna.

Does that sound OK?