Ultra-wideband and Highly Efficient Plasma-Matched Small HF Antennas
Abstract
PROJECT ABSTRACTApproved for Public ReleaseThe demand for wideband electrically-small antennas (ESAs) is rapidly growing because of(1) the need for compact and multi-functional devices, andradio-frequency range. However, small antennas are narrowband, non-efficient, and very difficult to be matched, especially over a wide frequency band. The promising point, though, is that if the matching issue is resolved, an ESA could potentially have an effective aperture as high as 98% of that of a resonant antenna. In an ESA, the frequency dependent antenna impedance consists of a very small resistance and a large reactance, which makes impedance matching necessary. However, implementation of such a matching network over a wide bandwidth using conventional passive elements is impossible due to the Gain-Bandwidth limitation. Non-Foster matching networks with an equivalent negative capacitance are required for wideband matching of ESAs. Although active negative impedance converters (NICs) and metamaterials have been extensively investigated over the past decade for this aim, these networks are complicated, lossy, and inefficient with poor stability performance.Plasma is the only natural material that can represent negative permittivity and so negative capacitance. Therefore, plasma matching networks can be utilized to compensate the negative reactance of ESAs over a wide, theoretically infinite, bandwidth. Plasma augmentation can significantly increase the efficiency of small antennas and thus, this technique can be a viable solution for efficient radiation with tuning capability. Thus, the overarching objective of the proposed effort is to design, develop, and demonstrate plasma-matched electrically small HF antenna elements and arrays with efficient radiation, high power handling, and reconfigurability schemes. This would specifically be a solution for space-limited applications where compact, multi-functional, lightweight, and efficient antennas are desired.Two different approaches will be taken for realizationof the proposed objectives: (1) ESA surrounded by a thin layer of plasma with designed thickness and electron density for impedancematching. The required energy for plasma generation is supplied from either the input signal to the antenna or an external source for transmitting and receiving scenarios, respectively. (2) ESA matched by a compact matching network which utilizes hermetically-sealed plasma cells. Compared to the first approach, this one would be more complicated, but more compact and easier for implementation. In addition, less power will be required for plasma generation as just small plasma cells will be used. Although the preliminary simulation and experimental results for realization of wideband and efficient ESAs look promising, there are several challenges that should be properly addressed to make this idea fully operational. The main challenges are plasmasheath thickness, plasma ohmic loss,the required high-power and wideband RF transformer with high impedance ratio, and the amount of power required for plasma generation. Although the concept of surrounding a small antenna by plasma to increase its radiation efficiency has been used before, those studies introduced high efficiency just over a narrow bandwidth. Also, they have been mainly focused on the received power and did not evaluate radiation efficiency as the main parameter of an electrically-small antenna. The goal of this research is to provide a systematic approach to design high-power plasma matching networks for realization of small antennas with high radiation efficiency, wide bandwidth, and tuning capability.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2021
- Source ID
- N000142112449
Entities
People
- Abbas Semnani
Organizations
- Office of Naval Research
- United States Navy
- University of Toledo