The 2013 MBA is using a new WiFi standard and there are bound to be bumps in the road with new hardware. Many people are using their new notebooks without experiencing WiFi connection/speed problems but obviously some are. You can be sure that Apple wants to get this solved as badly as you do and Mac sites have reported that an update is in the works.
In the meantime you can do a little troubleshooting of your own. Go to the manufacturer's Web site and make sure your wifi base station is using the newest firmware. If you have a 802.11 ac station be aware that the standards have been in flux for a while (but apparently are close to being agreed to now) so there may be incompatibilities that will have to be fixed with a firmware update yet to come. Again, if you do have an AC base station if it can be configured not to use AC that may be a temporary fix.