TP-Link router / fast wired, slow wifi

I bought a TP-Link TL-WR84N last week. I have a 50ft Ethernet cable connecting my ISP provided modem/router to the TP-Link router. The wired connection from the TP-Link to my computer is good (90mbps). However, the WiFi download speed is super slow (1.8mbps).
The router's firmware is up-to-date. (3.14.4 Build 131129 Rel.39318n)
The main reason I'm setting this up is for a stable Chromecast connection.

Any suggestions to improve the WiFi speed?