While I agree with Jeff that USB sucks, this is a decent USB wifi
dongle. The antenna is external via reverse SMA. It is quite cheap
through Data Alliance and these guys ship fast. I got this one and the N
version, though the 036H is the better long distance unit.
While it's fun to build antennas, there are some cheap wifi antennas
that are pretty good. Try the Laird PA24-16. The radiation pattern
doesn't have a lot of lobes. It is about $35 if you look around.
I built the wifi biquad a few years ago for yucks. It worked OK. There
are some tips on this list on how to build it since many of the websites
do it incorrectly.
I like these panel antennas. They are easy to transport. All the
elements are under a radome, so other than water infiltration problems,
they are well suited for outdoors. Avoid units that come with a pigtail.
It is better to have a connector on the back.
Given construction tolerances, antennas that depend upon aperture rather
than elements re-radiating the signal will work better. That is, a yagi
looks good on paper, but a lot depends on how tightly all the dimensions
are controlled. These panel antennas just sum a lot of smaller antennas,
so the bandwidth is broader and the design is more tolerant to
manufacturing tolerances. Some of these panel antenna are air isolated,
and some are just etched PCB. I would imaging the antenna with air
spacing works better, though I don't know if there is a list of how who