I am looking for wireless access point to provide internet service but it should be has DHCP server to provide IP addresses for clients because I would like to separate the clients from main LAN.
So long as you place the SSID on a different VLAN from your main network they will be separated. And can pull dhcp from any server that you have, which will be better suited to being a dhcp server than an AP will.
how big of a space are you needing to cover?
Please I would like to inform you that we have used this situation but my supervisor ask my for the type of access point that can have this option because we have some sites that are difficult to do that
By default, access points are configured to receive IP settings from a DHCP server on your network. You can also configure an access point to act as a DHCP server to assign IP settings to devices on both your wired and wireless LANs.
The 1100 series access point becomes a mini-DHCP server by default when it is configured with factory default settings and it cannot receive IP settings from a DHCP server. As a mini-DHCP server, the 1100 series access point provides up to 20 IP addresses between 10.0.0.11 and 10.0.0.30 to a PC connected to its Ethernet port and to wireless client devices configured to use no SSID, and with all security settings disabled. The mini-DHCP server feature is disabled automatically when you assign a static IP address to the 1100 series access point. Because it has a console port to simplify initial setup, the 1200 series access point does not become a DHCP server automatically.
Please refer to the below link for more information :