Modification and control of currents on an electrically long monopole using magnetic bead loading

With the growing demand for wireless communication systems has come growing opposition to increasing the numbers of cellular towers. A possible alternative to simply trying to hide the antenna mounting structure is to use parts of the existing environment as the radiating element. The simplest parts of an existing structure with which to begin such a study are conducting wires that may be part of an existing structure; these wires are electrically long at the frequencies where wireless communications are employed. To turn these electrically long wires into radiating elements, methods for modifying and controlling the natural current distribution on the wires are needed. We have investigated the use of magnetic beads to load an electrically long monopole and alter its input impedance and radiation properties. The current distribution can be shaped to resemble that of a quarter wavelength monopole. To obtain the required result, however, a magnetic bead with a large relative permeability was used, which may not be available at current wireless communication frequencies. Using alternating sections of magnetic and dielectric beads, it was found that lower permeability materials could be used to make the electrically long antenna behave as though it were a smaller element.