You can download the driver for your Realtek RTL8192EU wireless LAN adapter from the Realtek website or from other online sources, such as:

Features

Apple does not support Realtek chips natively. If you are running a Hackintosh or need to use this dongle on an older Mac, you must use third-party drivers.

A: This usually happens when the router is set to 20 MHz channel width only, or if the USB port is 1.1. Force your router to use 40 MHz width on the 2.4 GHz band and ensure you are using a USB 2.0 or 3.0 port.