near field probe bandwidth / size

[CopperCone]

So I see that you can make near-field probes out of coaxial cable thats looped.

Is there an upper limit on bandwidth that can be had with this method? I.e. can you take very thin hardline (0.086 and less) to make probes that are capable of sniffing emissions that are very fast? I see 10GHz near field probes available, but for 10,000$ each... however you can also buy a rf probe sniffer kit on ebay for 400$ and people seem pretty confident in making them for <5$ out of old hardline pulled out of test equipment.