Dual-feed, dual-mode antenna for mono-directional pattern

Abstract

A compact transmitting and receiving antenna has dual feeds permitting magnetic and electric dipole radiation. The antenna includes a loop antenna disposed within a loop shield and a mast. The loop shield is insulated from ground and a feed is provided to it and the mast to excite these as an electric monopole. The shield becomes part of the monopole antenna and provides the benefits of top-loading. An isolation transformer permits the simultaneous transmission of monopole and dipole radiation. The transformer converts an unbalanced coaxial feed line to the balanced loop antenna and isolates the monopole feed voltage from the loop antenna feed. To eliminate the affect of the monopole feed on the loop feed, and vice versa, the components on the high side of the monopole feed (the loop shield and mast) are driven in common mode (voltage) by the monopole feed, and will not couple the loop antenna feed through the transformer windings. Thus, with respect to the monopole feed voltage, both sides of the transformer windings connected to a loop antenna will be at the same voltage. No voltage drop across the transformer windings due to the monopole feed voltage will occur and hence no coupling to the loop feed transmitter will take place. The voltage insulation requirements are concentrated at the monopole feed point so that the isolation feed transformer takes all the voltage, making the loop, loop shield and monopole driven in common mode.