We study periodic structures constructed by low resistivity Si wafers which allow only the transmission of electromagnetic waves incident at a certain angle. We call those materials angular filters. The angular width of the transmission peak can be controlled by changing the thickness of the structure and/or by changing the resistivity of Si wafers. The basic idea behind the unusual properties of those materials lies on the Borrman effect or anomalous transmission of x rays through the crystals. Measured responses are in good agreement with theoretical simulations. Although the present structure was designed and built to work at around 100 GHz, similar structures can be designed for any other frequency region.