WiFi signal strength. Is there are ways to boost it.

I've got a new Latitude D830 laptop at work. Everything is fine and when I am working in the office my wireless network shows connection with the excellent signal strength.

However, when I am trying to use this machine at home, it shows signal strength as 'Very Low' and I am loosing connection frequently. At the very same spot my personal laptop (Fujitsu Lifebook) shows excellent signal strength. I checked with 2 other laptops - Sony Vayo and Dell Latitude D810. Sony was very good but Dell was very low.

I purchased and installed external antenna for my router but nothing changes.

Looks like it is something about Dell internal antenna. Can someone tell me if there are ways to improve it?

have someone else experienced same problem? 

Thanks.