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My design requires a NFC antenna to be located on a different board and due to space limitations, a uFL connector can't be placed for a mini coax connection. A flex cable solves many of the design issues. However, since a coax is shielded, will the flex cable need to be shielded too?

I am using the TRF7970A transceiver IC and the matching network will be placed on the flex cable, close to the antenna. The entire length of the flex would be 1.5". TI recommends matching the TX_OUT net to 50 Ohm Single Ended. So my intention was to breakout the 50 ohm trace to a FPC connector and then run a 50 ohm trace (referenced to a ground plane) on the FPC. The NFC antenna is a discrete component and will be mounted on a stiffener. Specifically, my question is as follows:

Since the coax is shielded, will the signal on the flex need to be shielded too? i.e. sandwiched between 2 ground planes? If so, adding a 2nd copper layer will significantly reduce flexibility and I might opt for a mesh plane, though from what I gathered, that might not work well for controlled impedance.

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Most NFC antennas I searched do have a mini coax. But I also bumped into a couple FPC NFC antennas, including one from Laird shown below (part number: 0600-00061), which don't have any shielding. So that made me think it's ok to just have a 2 layer FPC.

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NFC usually uses the ISM band at 13.56MHz. If this is true of your system, your signal has a wavelength of a little over 20 meters, so 1.5" of cable isn't going to create serious problems, and leaving it unshielded may even improve your signal strength a little bit.

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