If you want to cover the signal inside the restaurant well and don't want to set a password to prevent others from surfing the Internet, you can buy one with one or two antennas, and the transmission power is as low as possible. When you have set the route, you can try the signal around the restaurant with your notebook.

If it is still strong, you can put the router on the ground in the corner and use obstacles to weaken the signal strength in three directions as much as possible.

If you want to make it perfect, you can stick some tin foil on the wall when decorating, and the effect is quite good.