Development of a doorless access corridor for shielded facilities

The development of an access device for a large-scale shielded facility that requires no maintenance, can accommodate an unimpeded flow of pedestrian traffic, and may cost less than alternative access devices is presented. The corridor is composed of waveguides that attenuate signals over the lower frequency region of the overall electromagnetic spectrum and an absorptive or anechoic chamber that attenuates signals over the higher frequency region. The required attenuation of the waveguide and the reflection performance of the absorber material are determined by the attenuation (shielding) requirements of the facility. It is found through waveguide theory and modeling that a critical issue is the amount of shielding providing in the transition region above the waveguide cutoff and below the frequency range where the absorber material is most effective. Applicable theory is presented, design considerations are summarized, and a modeling approach is described. Actual construction details, which were used in two corridors currently installed and tested in large shielded facilities, are set forth.<>