Study and design of a broadband monopole antenna using non-Foster circuits

The possibility of using non-Foster circuit to expand the bandwidth of a monopole antenna is investigated theoretically. Beginning with an inductor-loaded monopole antenna resonating at different frequencies by changing the value of the loaded inductor, we show that a frequency-dependent inductor is needed to enhance the bandwidth of the monopole antenna. This enlightens us to use a non-Foster reactive circuit to realize the frequency-dependent inductor. Based on the above studies, simulated results demonstrate that the input reactance of the non- Foster loaded antenna becomes stable and approaches zero, which favours the impedance matching and extends the bandwidth to a certain extent. Finally, a passive (Foster) matching circuit is designed to improve the bandwidth further.