Analysis of a tunable electrically small antenna

A tunable, metamaterial-inspired, electrically small antenna topology is evaluated for a possible future use as the principle radiating element in a mobile Ionospheric Heating (MIH) system. The RF source signal is fed via a 50 Ω coaxial cable into a small semi-loop antenna (SLA). This inductively couples to a capacitively loaded loop (CLL) providing a natural 50 Ω match to the source. The resonant frequency of the antenna can be adjusted by varying the capacitance of the CLL via inserting a large permittivity dielectric. A simplified circuit model is used to show that the resonant frequency can be tuned between 40-100 MHz. Also, the maximum power handling capabilities achievable with this antenna topology at frequencies relevant to ionospheric heating (~ 10 MHz and below) are estimated.