The study described in this report was undertaken by the National Telecommunications and Information Administration (NTIA) in response to a Federal Communications Commission (FCC) Notice of Proposed Rule Making (NPRM) concerning the operation of a new class of spectrumdependent devices, designated as ultrawideband (UWB) devices under the FCC’s rules and regulations in Part 15 of Title 47 of the Code of Federal Regulations (CFR). This NPRM raises a number of questions and concerns regarding the electromagnetic compatibility (EMC) of the proposed UWB transmitting devices to those spectrum-dependent systems currently in operation. The NTIA, as the Executive Branch agency principally responsible for developing and articulating domestic and international telecommunications policy affecting Federal Government spectrum users, is particularly interested in the potential for interference to telecommunications infrastructure utilizing Federal Government spectrum for critical and/or safety-of-life functions, many of which operate in spectrum designated as the “restricted frequency bands.” These frequency bands have been designated as restricted because the systems operating in them provide critical safety functions. Before NTIA can agree to emissions from UWB devices in restricted frequency bands used by critical Federal Government radiocommunication systems, it must ensure that there is no potential interference introduced from their proposed operations. The Global Positioning System (GPS) is an example of a critical radionavigation system that operates in several of the restricted frequency bands.