Multiple methods are available to connect to Microsoft SQL Server.

If you run Radiator on Windows, use the ODBC administration tools and add a System DSN (data source name). Microsoft provides ODBC support for Linux and macOS with Microsoft ODBC Driver for SQL Server on Linux and macOS. The driver and installation instructions are available from the Microsoft web. For more about ODBC configuration on all operating systems, see Section 19.8. ODBC

To create a new database, see goodies/sqlserver-sybaseCreate.sql for more information.

Configure your SQL clause like this:

DBSource    dbi:ODBC:radius
DBUsername  radius
DBAuth      password

If you can not use Microsoft ODBC driver, consider DBD::Sybase with FreeTDS. Sybase and MS SQL Server have common history and for this reason DBD::Sybase is known to work with Microsoft SQL Server. You need to compile and link DBD::Sybase with FreeTDS libraries. For more about DBD::Sybase, see Section 19.9. Sybase

Yet another option is to use the ODBC driver that comes with FreeTDS and configure Radiator to use DBD::ODBC. For more about DBD::ODBC, see Section 19.8. ODBC