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Anitha
Anitha
Associate III
July 20, 2019
Solved

Two antenna's and unfitted capacitors in MB1355 schematics

  • July 20, 2019
  • 4 replies
  • 2741 views

0690X000009YwROQA0.jpgHi Sir,

In the MB1355 schematics what is the purpose of two antenna's?How to calculate the unfitted capacitors ? what is the purpose of band pass filter here?

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Best answer by Remi QUINTIN

The MB1355 board is used to prototype application. So, we have implemented 2 RF outputs: one to SMA coaxial connector for external antenna or for conducted measurements, and one PCB antenna to present BLE Over The Air demonstration with a smartphone or another BLE board. the customer chooses one of those 2 RF outputs.

 On the PCB antenna side, the components are indicated. Only one capacitor is unfitted, but it is spare footprint and is never used.

On the SMA side, if you make conducted measurements, no component is necessary. If you put external antenna, the values of the components depend of the antenna impedance connected.

4 replies

Remi QUINTIN
Remi QUINTINAnswer
Technical Moderator
July 22, 2019

The MB1355 board is used to prototype application. So, we have implemented 2 RF outputs: one to SMA coaxial connector for external antenna or for conducted measurements, and one PCB antenna to present BLE Over The Air demonstration with a smartphone or another BLE board. the customer chooses one of those 2 RF outputs.

 On the PCB antenna side, the components are indicated. Only one capacitor is unfitted, but it is spare footprint and is never used.

On the SMA side, if you make conducted measurements, no component is necessary. If you put external antenna, the values of the components depend of the antenna impedance connected.

Anitha
AnithaAuthor
Associate III
July 25, 2019

Hi Sir,

If I want to use only SMA antenna do I need RF switch capacitors? I'm thinking below one is the circuit, if want to use only SMA antenna. let me rectify if I wrong.

may I know the output impedance from RF1 pin in STM32WB55REV?0690X000009Z5U3QAK.png

Remi QUINTIN
Remi QUINTIN
Technical Moderator
July 25, 2019

If you want to use only the SMA antenna, you have to solder the capacitor in the SMA antenna path and remove the capacitor in the PCB antenna path.

It is not necessary to know the output impedance from RF1 pin because the matching network has been calculated to present 50 ohms at the output of the filter towards the antenna path.

Anitha
AnithaAuthor
Associate III
July 26, 2019

Hi Sir, Like below way only you are saying? Can you tell way to calculate highlighted capacitors(means formula to calculate the these Not fitted capacitors?

0690X000009Z7RVQA0.png

Anitha
AnithaAuthor
Associate III
July 27, 2019

Can you please clarify the above question?

Remi QUINTIN
Remi QUINTIN
Technical Moderator
July 26, 2019

​No issue. The OTA is not linked to the type of antenna.

Marc Laury
Marc Laury
Visitor II
August 21, 2019

In the MB1355 schematics what is the purpose of two antenna's? You have one PCB if you want to use the embedded antenna on the board or you have a SMA connector to connect an external antenna if you have your antenna.

How to calculate the unfitted capacitors ? If you connect an external antenna which presents 50 ohms, you do not need adaptation network for this antenna, but if you connect an external antenna which does not present 50 ohms , you have to define the components of the adaptation network. A lot of documentation is available on the web to do it.

what is the purpose of band pass filter here? This band pass filter is to eliminate the harmonics but also the others unwanted signals from others systems.

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