Extending wifi reception distance from my router

Hi All,
I've just built myself a little shed at the bottom of the garden to escape to, and I can't get a wifi signal in it to my laptop from my router even though it's on maximum power. I don't want to buy a new one as it's a top of the range 802.11n Netgear and only six months old. I don't want to muck about with long LAN leads either or boost the power of the Router as that will increase the risk of it getting hacked.
The shed power supply is on a different phase to the house so I can't use the electrical socket option.
What I really need is something USB that I can plug into my laptop so it can receive from as far away as possible. Any advice would be most welcome. Thanks in advance.

THere are USB wifi adapters that allow for external antenna connections, one of these could work. You'd also need an antenna, perhaps directional.
Or, you could buy an access point that works like a client. One manufacturer of these is ubiquiti, another is highgainantennas. I've got one of each. They both have a built in directional antenna setup. You plug it in, connect an ethernet cable to it and your laptop. After some simple configuration, you'll then have internet at the laptop end of the ethernet cable whenever you want it. It is acting like a big wifi adapter, but has the power and antenna built in to it already. You'd point it at the house...and depending on distance and material (foilage being the big problem) you should be up and running.
The USB adapters work also, but now you're buying an antenna, and still schackled to your shed.
You could try a higher power usb adapter, with just a stubby antenna. If it works, you'd have a little more portability. If it doesnt, then you'd have to add an antenna. How far from the shed are you when you lose the houses wifi signal?