SMA connector and 3.5 mm conector

No, they aren't.

1- they are mechanically compatible but not electromagnetically.

2- fmax(SMA) = 18 GHz
fmax (precision 3.5mm)=34 GHz
fmax (standard 3.5mm)=26.5 GHz

3- SMA dielectric : teflon
3.5 mm : air

These are the main differences.

regards

Marco De Dominicis

Since they are not same at interface,when mating them together,be carefule thre is a step capcitance on it outter conductor and will influence high frequency performence.