On the stability of non-foster monopole antenna arrays

Non-Foster circuits (NFCs) promise to improve the gain of electrically-small and superdirective antenna arrays by at least 10x by cancelling the self and mutual reactances over wide bandwidths, thereby overcoming the Fano limit. To the authors´ knowledge, however, there are no reports of NFCs being successfully integrated into antenna arrays. A 2-element monopole array (length and spacing 15 and 3 cm respectively) whose self and mutual reactance is substantially cancelled over 10-300 MHz employing three negative-capacitance NFCs has been realized. The NFCs are integrated into a single integrated circuit that consumes 50 mW of DC power. The analytical stability model is consistent with the experimental data, demonstrating that series and interelement NFCs are necessary to cancel the reactance of both the even and odd modes.