Frequency Selective Surfaces for Long Wavelengths

移动通信和无线计算机网络已经非常流行，用户数量和系统类型将继续增加。每个系统都需要使用一定的传输频率，这些频率必须以某种方式分离以避免干扰。负责颁发无线电频谱许可证的政府机构OFCOM正开始放松对无线电频率使用过程的管制，设计一种使无线电环境更不受干扰、更不受窃听的方法至关重要。此外，不允许使用电话的囚犯也在使用偷运到监狱的移动电话。这些电话被用来组织外部犯罪，走私毒品，协调逃跑和暴乱。这引起了监狱当局和英国政府的极大关注，因为在技术上很难在不干扰监狱附近无辜用户电话的情况下阻止手机通信。与上述问题平行的是，现代建筑内衬金属层用于隔热。这一层屏蔽了建筑物内部，可以显著降低通过建筑物内部的无线电信号的强度。这可能会减少建筑物内应急服务使用的无线电系统的覆盖范围，使人员处于危险之中。这项研究旨在创造频率选择表面（FSS），在通过授权服务使用的频道时过滤掉移动频率的无线电信号。FSS设计将卷曲和交织以压缩其尺寸，并将安装在金属屏蔽墙的小孔中。通过将开关二极管集成到设计中，将达到指定的隔离级别，并使性能具有适应性。计算机模拟将用于预测信号通过FSS并进入房间的传播。

Mobile communications and wireless computer networking are already enourmously popular with user numbers and system types set to continue increasing. Each system requires the use of certain transmission frequencies which must be separated in some way to avoid interference. OFCOM, the government body that licences the radio spectrum is beginning to deregulate the process of radio frequency usage and it is vital to devise a means of making the radio environment both more immune from interference and safe from eavesdropping. Also prisoners who should not be allowed access to telephones are using mobile phones smuggled into prisons. The phones are used to organise crime outside, smuggle in drugs and coordinate escapes and riots. This is of great concern to the prison authorities and the UK government as it is technically difficult to stop mobile phone communications without interfering with the phones of innocent users near the prisons. Parallel to the above issues is the fact that modern buildings are lined with a metallic layer for thermal insulation. This layer screens building interiors and can significantly reduce the strength of radio signals passing inside. This can reduce the coverage of radio systems used by the emergency services within buildings placing personnel at risk. This research seeks to create Frequency Selective Surfaces (FSS) to filter out radio signals at mobile frequencies while passing channels used by authorised services. The FSS designs will be convoluted and interweaved to compress their size and will be mounted in small apertures in metal screened walls. A specified isolation level will be aimed for and the performance will be made adaptable by integrating switching diodes to the design. Computer simulations will be made to predict the propagation of signals through the FSS and into rooms.