Electrically small, circular inverted-F antenna based on a robust, minimal design space

A printed circular inverted-F antenna (CIFA) is mirrored against a small, crescent-like ground plane (GNDP). The whole radiator is printed on a discoid substrate that conforms to the element and the ground plane. The edge of the PCB conforms to the circumscribing sphere. The CIFA-plus-GNDP combination is an electrically small element designed with only three parameters: two angles and a radius. It is resonant and matched at 2.5 GHz, where it achieved a 3.5% fractional impedance bandwidth. The antenna is highly efficient (91-95%) and approaches Thal's limit on minimum Q-factor within 27%.