Let me make clear just what those Superhub antennas actually are.
A 3cm x 1.5cm PCB making the antenna about a half wave dipole at 2.4GHz. There are two PCBs each mounted at about 45°. This is reasonably efficient but most routers come with one or more external antennas typically offering 4dB of gain over a dipole. You can also usually replace the supplied external ones with alternatives which offer higher gain. Gain is achieved by favouring one direction at the expense of another - typically by "squashing" the vertical radiation on the rod style antennas sold (search for collinear antenna if you want a better explanation).