Active Antennas Beyond the Standard Impedance Matching Technique: Concepts and Applications

This paper presents a new design concept for improving active antennas’ performances beyond the standard impedance matching technique. The proposed approach expands the mismatch at the antenna-amplifier interface to create a voltage excess, transferred to the matched output receiver using a voltage-type amplifier instead of a power type. Compared with a standard dual-input-output matching, this leads to comparable bandwidth and DC consumption but significantly improves the peak gain, gain-bandwidth-product (GBWP), stability, and noise figure. Experiments with a conventional dipole antenna confirm an improvement factor near two on gain and GBWP. Stability improves by 10°, tending to reach the reference value of 60° phase margin for sound systems. Also, the noise figure significantly decreases by 4.5 dB on average. In addition, the newly introduced performance metric, typically normalized gain-bandwidth-product (NGBWP), dividing GBWP by the average amplifying stage’s gain and the passive antenna’s GBWP, is NGBWP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${=}6.84$ </tex-math></inline-formula>, far higher than the existing works peaking at 2. Finally, the proposed active dipole shows GBWP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${=}2.68$ </tex-math></inline-formula>, which is 15 times the passive dipole. These attractive characteristics make the present approach suitable for most wireless systems.