After the new U-NII rules came out, vendors began to look at the requirements for type acceptance, and discovered a problem that, if not fixed, potentially guts the benefits of the new rules and, because the old rules expire, makes the situation far worse than the status quo. The problem concerns the specific requirement for out-of-band emissions allowed under U-NII rules (15.407), which are computed differently from the old ISM-band rules (15.249).
To simplify it, 15.249 says that out-of-band emissions usually have to be 30 dB below the desired emissions. It's a relative value ("dBr"). There are other out-of-band limits too, but this is the key one. So if you look at the spectrum trace of a typical 20 MHz signal, it's down by 30 dB soon enough (sometimes even within 5 MHz). If your transmitter power is 1 watt (the limit, +30 dBm) and antenna gain is +25 dB, EIRP is +55 and out-of-band EIRP can be +25, or +12 dBm/MHz. That's how MikroTik radios are approved. And everybody else who supports 5725-5850 also uses 15.247 approval, even if they have 15.407 (U-NII) for the DFS bands, because 15.247 grants more capabilities and is easier to meet.
The new rules do away with 15.249 for new equipment but nominally allow unlimited EIRP under 15.407 from 5725-5850. The problem is that 15.407's spec for out-of-band is not relative, like 15.249. Nor is it a fixed transmitter power. It's a fixed EIRP. The signal has to be at -17 dBm/MHz at band edge and -27 dBm/MHz at 10 MHz from band edge.
This was never a problem for U-NII-II (5250-5725) because the EIRP limit there was +30 dBm and +17 dBm/MHz, so meeting -17 dBm/MHz was only 34 dB. Not a huge deal. And it wasn't a huge deal for omni access points, because the PtMP limit was +36 dBm EIRP, and thus a 40 dB ratio was achievable with, say, 10 MHz guard band.
But getting past 40 dB is really hard. If you are using a 23 dB antenna and a +30 dBm transmitter, you're at +53, the PtP limit for the new U-NII-1 band, and of course there is no EIRP limit for PtP above 5725. But wait... +53 dB EIRP = +40 dB/MHz = +57 dBr against -17 and 67 dBr against -27 (10 MHz away). No, MikroTik can't meet that. Nor can brand U, brand C, brand M, or anyone else. And if you have a radio approved for a certain antenna gain, it might be out-of-approval with a higher-gain antenna -- which is silly, since high gain antennas focus the out-of-band as well as in-band signals, reducing actual interference.
There are two petitions now before the FCC to fix this. WISPA's simply calls for the old 15.247 rules to remain in effect, so nobody needs to transition to 15.407. Mimosa's calls for 15.409 to be modified so that out-of-band is allowed to go up by 1 dB for every dB of antenna gain above 6 dB. That equates to 40 dBr worst case, PtP, for U-NII-1 and U-NII-3.
You can go to the FCC's Electronic Comment Filing System (you know, the one that was totally clobbered by last week's NN filings
) and go to (ET) docket 13-49. You can see the WISPA and Mimosa petitions, as well as filings from Cambium and others in agreement. My comment is there (under the name of Interisle Consulting Group, my firm), supporting both Cambium and WISPA. Some of you may want to weigh in. I don't know of a date for closing Comments; this is still just a petition, not a rulemaking.