Just in case anyone else comes by and sees this thread, I'd like to point out thst in my all-too-extensive experience, an external antenna is not a must.
The printed circuit antennas inside phones and routers (yes, inside particularly Huawei ones) are fantastically good.
In many situations adding an external antenna will add cost and hassle, but won't improve performance, even if it increases the signal strength on the display.
The important measure is signal quality, not signal strength. An external antenna can reduce signal quality and can stop diversity for multiple antennas working properly.
I have an external antenna on a built-in slide-up pole, which I've not even bothered to use for a couple of years. The router works just fine without it.