Improved low-height antifading medium-wave antenna

A new type of antifading broadcast antenna, consisting of typically four base-excited sloping wires located symmetrically about a central insulated support mast, offers significant advantages over conventional loaded antifading radiators. These advantages include a higher loop radiation resistance for mast heights below approximately 0.4¿, less inductive loading, and multiple parallel earthing points that are expected to reduce the earth losses when the soil is of low conductivity. The radiation resistances and associated antifading radiation patterns have been computed using two techniques; one with assumed sinusoidal-current distributions on the sloping wires and assumed negligible induced mast currents. The other involved a moment method analysis employing subsectional bases for the wire and mast currents. Results given by the first method agree well with both measurements performed on models having a nonmetallic mast, and the predictions given by the second method for masts having three or four insulated sections. If only two insulated mast sections are employed the induced mast current lowers the radiation resistance significantly; whereas, with a single continuous conducting mast section, the radiation pattern loses the required antifading form. It is considered that the new antenna will lower the minimum practical height of antifading radiators from the present value of approximately 0.35¿ for conventional loaded monopoles to somewhere in the range 0.25¿ to 0.3¿.