Impedance Matching in Small Antennas through Capacitively-Coupled Plasma Technique

The demand for electrically small antennas (ESAs) is primarily driven by the need for compact, multi-functional devices operating in the low radio-frequency range. However, ESAs inherently suffer from narrowband characteristics and low efficiency. Theoretically, it has been demonstrated that wideband matching of ESAs is achievable by employing non-Foster matching networks that represent negative capacitance. In pursuit of this theory, various approaches, such as active negative impedance converters (NICs) and metamaterials, have been investigated over the past decade. However, these networks often exhibit complexity, significant losses, and limited stability performance, which hinder their practical implementation.

This study presents a novel approach utilizing capacitively coupled plasma for achieving wideband matching in small antennas. The proposed technique leverages the negative permittivity properties of plasmas, enabling the realization of a negative capacitor within a capacitively coupled structure. By utilizing the negative capacitance of the plasma, it becomes possible to compensate for the reactance of small antennas across a wide bandwidth. Experimental data confirming the successful implementation of this technique will be discussed. The results demonstrate the effectiveness of the plasma-based approach in achieving efficient radiation over low-frequency ranges, particularly in high-power (transmitting) scenarios.