A microstrip meandering-line antenna for a wireless communications system includes a substrate, a meandering-line conductor, and a feeding wire. In addition, a main body humidity sensor detects information about atmosphere humidity of a main body of the image forming apparatus, and a main body temperature sensor detects information about temperature of a main body of the image forming apparatus. The foamed films of the present invention are thin, and have an MD tear strength of at least about 160 grams for a 3 mil film as measured by ASTM D 1922.