The present invention provides a glass cloth suitable for producing a printed wiring board to be used in the electronics and electric fields, which has small anisotropy in dimensional change and is free from warpage and twist, a prepreg using said glass cloth, and a printed wiring board using said glass cloth. The insulative housing has two side walls and a slot between the side walls. In addition, countermeasures against a system according to the invention are difficult because the signal waveforms for each beam are distinct and random, making prediction of any signal waveform for any beam very unlikely.