Next generation ionospheric heater antenna

Abstract

An electrically small, three dimensional metamaterial inspired antenna at MHz frequencies is evaluated for its potential future use as the principle radiating element in a Mobile Ionospheric Heating (MIH) installation. The design consists of a small loop antenna (SLA) which inductively couples to a capacitively loaded loop (CLL) providing a high Q with a natural match to a 50 Ω source. At approximately 2.5 × 3 × 1.2 m in size the antenna is significantly smaller than the element, 21 × 21 × 16 m, used in the High-frequency Active Auroral Research Program (HAARP) array designed for ionospheric modification. With a gain upwards of 7 dBi when mounted above a sufficiently large ground plane, and up to 90 % efficiency, this electrically small antenna, ESA, provides a compact, efficient radiating element as a standalone radiator or as part of an array. It is demonstrated that tuning from approximately 3 to 10 MHz is possible via adjustment of the capacitance in the CLL and the mutual inductance between the SLA and CLL. A full-scale prototype antenna was fabricated and evaluated to obtain experimental radiation efficiencies and patterns at 500 W power levels, which compare favorably to simulations. Scaling for array operation revealed that it is conceivable to generate 3.6 GW ERP power in equatorial zones from a transportable platform based on the ESA. Such power levels suffice effecting ionospheric modification and, for instance, ELF wave generation in the range of 1–70 Hz.