The making of small but mighty antennas

Smaller antennas have smaller bandwidth and thus lower performance, which limits antenna miniaturization. But recent research has begun to overcome this limitation with time-varying circuit elements that can be used to enhance the operational bandwidth of small antennas.

Most existing approaches employ fast time-varying reactive elements that utilize double-frequency modulation. However, Mostafa et al. engineered the operational bandwidth of a small antenna with a resistive element that varies slowly in time.

The authors demonstrated that slow modulation of the resistance induced virtual impedances, which they could use to enhance the power radiated from a small antenna at multiple frequencies simultaneously.

“Our work is one of few works to slowly vary a resistive element to engineer the bandwidth of highly resonant structures. The proposed approach has multiple advantages over similar works that leverage time-modulation to enhance operational bandwidth,” said author Mohamed Mostafa.

The slow modulation of this approach is easier to execute than conventional fast modulation. This technique is also unconditionally stable and does not require power pumping, whereas fast time-varying reactive elements are prone to instabilities and need to pump power to achieve bandwidth enhancement.

“We explore new means to engineer the bandwidth of highly resonant structures —not only antennas — through varying resistive elements in time, paving the way for more investigations in this direction,” Mostafa said.

In this work, the authors connected a time-varying resistive element in series to a load antenna. Next, they will figure out how to adapt this technique to practical devices, which will require the source or load resistance itself to be modulated in time.

Source: “Antenna bandwidth engineering through time-varying resistance,” by M. H. Mostafa, N. Ha-Van, P. Jayathurathnage, X. Wang, G. Ptitcyn, and S. A. Tretyakov, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0133016 .

This paper is part of the Time Modulated Metamaterials Collection, learn more here .