As far as I know, to do this would actually require multiple WiFi antennae. Your phone only has one. It can receive a signal, or broadcast a signal, but not do both at the same time.
There is software available that allows wireless tethering from your phone to the PC via Bluetooth, if you'd like. Ie, Home WiFi > Phone > Bluetooth signal > PC.
It's also possible to simply connect your phone to the WiFi, then connect the phone to your PC via a USB cable and tether that way without any additional software or apps.
Either way though, you're going to lose a lot of speed in the process. You're likely better off buying a high gain antenna and pointing it in the direction you need.