There's a syncthing wrapper for iOS (Möbius Sync), which is free up to 20 MB of synced files. The unlimited version only costs $5 once, so might be worth it.
Otherwise I'm sure there's ways to set a network fileshare on your PC, that you can access from your iPad (if you only need it in LAN).
If a Yagi is not broadband enough, look into Log-Periodic antennas. They are similar to Yagis, but can be built with a very large bandwidth.