  We introduce the concept of a Rotman-lens spectrum decomposer (RLSD)
real-time spectrum-sniffer (RTSS) for cognitive radio. Compared to a previously
existing RTSS, the RLSD-RTSS offers the advantages of being 1) based an a
simpler and lower-cost purely passive structure, 2) easier to design and easily
amenable to tunability, 3) of much broader bandwidth, and 4) of accommodating
more channels. The electrical size of the device is electrically larger, but
perfectly acceptable in the millimeter-wave frequency range. The proposed
RLSD-RTSS is demonstrated theoretically and experimentally, and been shown to
support tunability in terms of both bandwidth-resolution and operation band.
Given its unique features, this device may find wide applications in 5G UHD and
3D video systems.
