Why wont my iphone connect to my home wifi?

I have an iphone and its been connecting fine but lately it has sometimes disconnected from my wifi but i could go to the settings and reconnect again but now it stays permanetely on 3g network and when i go to setting is doesnt even show my wifi even when it is know nor will it connect when i type it in right but on my ipad its on the same wifi please help

Change the settings in the router, or try tapping forget this network and start from scratch. But it sounds as if somebody mess around with the router and use a stronger encryption which sometimes gives some trouble connecting when it comes to Apple products.
My recommendation? Change the settings in the router.