I have a router that is kind of portable and seems reliable but not pocket size and might be a bit too big for your requirements and one problem with it is that it is a Huawei and it's 4G only ar 150mbps.
Hauwei E-5172
https://www.amazon.co.uk/Huawei-E5172As-22-150Mbps-Unlocked-Wireless/dp/B00GHK3XOCIt has room for a built in battery backup battery but I have one firmware that disables most of the functions but the mobile and phone adapter and the other leaves everything on. I carry one around with a 12v powerbank on the back.
It has:
12v 1a input
Battery compartment for 3x aa NiMH battery pack.
100mb ethernet port.
Wifi N
Internal aerial and 1 x external sma plug, set to auto and can be selectable in built in webserver.)
Analogue phone converter (auto switches to 3g on my mobile service.)
I got a couple from Portugal much less than that on Amazon for about £40 each in 2018 and I am using one as a backup for my broadband and VOIP converter.
I used it in a chicken barn in 2018 in a farm in the middle of nowhere and the signal was a lot better than this EE pocket WIFI thing I had and even outside.