Lolol. (Unless you meant kg)... You could mount it directly to stepper shaft. But technically risk eventually wearing out motor.

Maybe a small right angle gear box. https://www.ondrivesus.com/miniature-gearboxes

You certainly don't need any significant bearings.

I would personally hose clamp tubing between the two shafts as a coupler and put little wheels/dollies/ upside down ball bearing wheels for antenna assembly.