I was reading a datasheet for an Ethernet Interaface Layout from NXP and I found they didn’t use reference plane in the region where they routed the differential pairs. I couldn’t understand why they do that and I didn’t find an answer. The datasheet explains it that they wanted to reduce the capacitance but how the signal couples? It couples only with each other? enter image description here

Datasheet: AN2759 page 16

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