Adding a Reflector to your Modem Antenna can increae the Range of your WiFi Signal. This method is suitable if your Modem is placed in one corner of the house and you want to increase the coverage in a directional maner. My BSNL modem operates at a WiFi frequency of 2.4 GHz and I have added a reflector as shown which gives me approximately double the WiFi Range.

The Sketch above gives the dimentional details of the Antenn Reflector and the Assembly.