It's fairly straightforward from Santa Clara Caltrain service, however on a Saturday the Caltrain service frequency is fairly scarce, so you'll have to carefully plan the schedule. From Santa Clara station there is regular bus link to the airport or you can just take a taxi for that last section, it's less than 10 minutes. If you're trying to keep it simple, the alternative is to take the BART all the way down to Warm Springs, the end of the line, and a taxi/Uber/Lyft from there. That runs often enough,, it's 20 minutes from Warm Springs to the airport.