Extremely electrically small antennas (XESAs) exhibit low gain performance, which seriously limits their applications in space-constrained wireless platforms. We report an active transmitting XESA whose gain-bandwidth product (GBWP) exceeds the passive Bode-Fano upper bound. It is realized by incorporating a highly efficient, electrically small, near-field resonant parasitic (NFRP) antenna into the feedback loop of an operational amplifier (OpAmp). Rather than a cascaded configuration, the innovative structural embedding of the NFRP antenna directly with the OpAmp circuit significantly increases its effective gain without consuming any additional real estate. The operating mechanisms of the integrated system are explained with an equivalent circuit model. An optimized prototype was fabricated, assembled, and tested. The electrical size of its radiating element is extremely small with ka = 0.15 at 414 MHz, i.e., $a~\approx \lambda $ /42. The measured results of this active XESA, in good agreement with their simulated values, demonstrate that its effective gain can be dynamically tuned within a 6.01 dB range. The measured maximum effective gain and, hence, the effective isotropic radiated power (EIRP) witnesses a 9.152 dB (8.23 times) improvement in comparison to its passive counterpart and its measured GBWP surpasses the corresponding passive Bode-Fano upper bound by approximately 15.2 times.
- Active antennas
- electrically small antennas (ESAs)
- near-field resonant parasitic (NFRP) elements
- operational amplifiers (OpAmps)
ASJC Scopus subject areas
- Electrical and Electronic Engineering