Which versions of the Raspberry Pi are HAT compatible with?

The HAT is compatible with all Raspberry Pi which contains 40W GPIO header.

Do I need external antenna for GNSS/GPS?

Embedded GNSS/GPRS antenna is available on the GNSS/GPS module.
There is also an option to use an active external antenna also, which needs the following
modification in the GNSS Antenna Jumper to be changed as following.
Click here to see.