Modelling of EMC screens for radio base stations. Part 1: Experimental parametric study

Enclosing electronics in sealed metal boxes provides good electromagnetic shielding, but evidently restricts the air movement necessary for adequate cooling. In order to meet ElectroMagnetic Compatibility (EMC) requirements, a perforated plate (an EMC screen) must be used. The design of this screen must provide a sufficient free area ratio for the adequate airflow, but at the same time the holes must be small enough to block electromagnetic radiation. An experimental set-up that represents a Radio Base Station (RBS) subrack was built inside a wind tunnel. The airflow pattern and pressure drop through the EMC screen were investigated experimentally for different subrack geometries, screen porosities and velocities, and the recirculation zones were identified. The study was performed by means of pressure and velocity measurements, together with smoke visualization under isothermal conditions.