CC2640R2F: Inverted-F Antenna

Gözde C

Part Number: CC2640R2F
Other Parts Discussed in Thread: CC1350, CC2640

Hi,

We will use an inverted F-antenna in one of our designs, and there is something we cannot understand the logic of when integrating this antenna into our PCB design: A part of the inverted F-antenna used for 2.4 GHz in CC1350 or CC2640R2 is connected to GND. In this case, the entire antenna becomes GND. I can't understand how the antenna would broadcast like this. Could you please explain why.

Thanks in advance for your answers.

over 3 years ago

+1 Jake Pulliam over 3 years ago

TI__Expert 6520 points

Hi Gözde,

This would act as short at DC or low frequencies. However at RF the short to ground acts as an inductance. It is used for impedance matching the antenna to 50-ohm. There are quite a few papers and resources that describe antenna theory which is too large a topic to cover here. You might check out https://www.antenna-theory.com/antennas/aperture/ifa.php which has a good brief overview.

0 Gözde C over 3 years ago in reply to Jake Pulliam

Prodigy 60 points

Thanks for your answer. So, how do I connect the part of the antenna that goes to ground directly to gnd without using a via like in the image?

0 Jake Pulliam over 3 years ago in reply to Gözde C

TI__Expert 6520 points

The plane that it is connected to is on the same layer as the antenna. That layer would then be tied to a ground reference plane with many vias. See any of our reference designs for examples of how this is done. For example:

from https://www.ti.com/tool/CC2650EM-7ID-RD

Jake

0 Gözde C over 3 years ago in reply to Jake Pulliam

Prodigy 60 points

Only this way it connects to ground using via. There is a gap between the ground plane and the antenna and they are not connected.

0 Jake Pulliam over 3 years ago in reply to Gözde C

TI__Expert 6520 points

I'm not sure why that was done that way, what design is that from? Was that a TI design?

edit:

I'm sorry, I think I misunderstood what you were asking. Are you asking how to create the correct antenna design in your design software?

-Jake

0 Gözde C over 3 years ago in reply to Jake Pulliam

Prodigy 60 points

To tell you from the beginning; I tried to add the antenna that TI used for 2.4 GHz in the CC1350 or CC2640 reference design to our design. I drew the antenna as a polygone according to the dimensions in the document of this antenna. The antenna has both a feed and a gnd connection. But I can't make the gnd connection as in the original design. Antenna cannot be connected directly to ground. There is a gap between the antenna and the ground and I can only connect the gnd via via. So yes, how can I make the antenna design the same as the original design?

I hope I was able to explain clearly.

0 Jake Pulliam over 3 years ago in reply to Gözde C

TI__Expert 6520 points

Yes that makes sense. It sounds like the layout rules are preventing overlap between the antenna and the plane. Unfortunately I can't provide support for your CAD design software. You will need to seek support from the software company or other community resources.

Jake

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CC2640R2F: Inverted-F Antenna