You can add a simple <$50 wireless router of any make to your your existing network infrastructure and configure it as an Access Point rather than a Gateway. This allows access to all resources by wired and wireless users. To do so, see the following instructions and the diagram of the physical connections below:
- Reset the new router’s wireless WAN connection to default, i.e. un-configured
- Assign the new router’s LAN side an IP address in the same subnet as the existing router (see diagram below). Make sure the IP does not conflict with your existing DHCP service, whether using the router or a server as a DHCP server, and make sure it doesn’t conflict with any statically
assigned devices, if any, such as printers - Disable DHCP on the new router
- Configure the wireless connections on this router in the normal manor. If your primary router is wireless the second router will need to use a different SSID
- Connect a cable from one of the LAN ports of the primary router to one of the LAN (not WAN) ports of the new router. If the lights do not light up indicating a connection you may need a cross-over cable (usually only necessary on older units)
- Now all devices should have Internet access and be able to easily connect to one another to share resources.
LAN-Tech Network Management 
Comments on: "Add a wireless router/access point to an existing network" (5)
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I put two more access point from the new wireless router ,cable is from 1st ap Lan port to 2nd ap Lan port then 2nd ap lan port to 3rd ap Lan port, izzit correct ? Then ip will be 1.2 , 1.3 ,1.4
If your access points have 2 ethernet ports you can “daisychain” them (connect one to the next and then the third), but there is no guarantee the IPs will be sequential. You can assign DHCP reservations based on the MAC addresses or with most access points you can set a static IP.