The nRF2401L is not really WiFi. It doesn't do frequency hopping or any spread spectrum.
Anyway - the antenna probably cannot be connected with ribbon cable - it would be inefficient. Most of the cables found (for example, on Amazon) for this purpose are fairly high loss (RG174, RG58, etc). There are low loss cable assemblies you can buy for 2G/3G/4G that have SMA connectors on them. RFparts.com has some better ones (type 195). So, if you connect an SMA connector to your nRF2401L, and use the low loss (designed for 2G/3G/4G) cables, you may be OK. The way the connection is made is pretty critical due to the extremely short wavelength. Otherwise, just use the built-in or directly connected antennas.
There's not much signal there to begin with. The nRF2401L is used in some wireless mice (probably the main reason for it), so that gives you an idea about the range they have (although the mice may run the chip at one of its lower power settings, and that is adjustable depending on locale).
Some people use the high loss RG174, but over any significant length it degrades the signal. It depends on your application. I have in the past ordered "hard line" for this purpose (hard, aluminum, non-flexible jacket cable that can be bent in the same manner as thin copper tubing for example) - but it's overkill for most projects.
The GPIO connections to the Pi are SPI serial.
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