Highrise Building Reradiation and Detuning at MF

An evaluation of the reradiation from highrise buildings in the MF broadcast band is presented. Scattered field measurements were made at MF on buildings of the order of one quarter wavelength in electrical height and at UHF on scale models. A computational model incorporating the effects of lossy ground and building materials was developed using moment-method techniques. Reduction of scattering is demonstrated, both for models and a full-scale building, using simple wire detuning stubs to modify the induced RF currents. The current distributions resulting in the decrease of scattering are described for a vertical stub like those used in power line detuning, and for two related new designs, a rooftop stub and the "umbrella" stub. The latter is shown to be the most effective, yielding scattered field reductions of the order of 6dB in fullscale tests.