Plasma Antenna Research Articles

Effect of the method of excitation of the plasma antenna on the spectral characteristics of the radiated signal

The radiation of signal by the plasma asymmetrical vibrator antenna is studied for two methods of its excitation. Earlier, it was shown that the 2nd and 3rd harmonics of the input signal frequency in the radiation spectrum of the plasma antenna are 10—20 dB stronger than those of a metal antenna with the same geometry. In this work, we study experimentally and by computer simulations the effect of the method of excitation of the plasma asymmetrical vibrator antenna on the spectral characteristics of the signal that it radiates. For the two excitation methods of the antenna, through an electrode and through a coaxial coupler, it was shown that the strength of the signal components at the frequency of the radiated signal and its multiple harmonics is different. The introduction of the coaxial coupler in the antenna excitation scheme allowed us to improve the coupling at the input signal frequency and decrease its components at the 2nd and 3rd harmonics. For the plasma antenna with the coaxial coupler, the difference between the 1st and 2nd harmonics was increased by almost 6 dB, and between the 1st and the 3rd ones by almost 20 dB compared to the antenna excitation scheme through the electrode.

Plasma antenna with frequency adjustment

A discharge of limited length (“plasma column”) in a gas-discharge tube filled with a rarefied gas was studied. The discharge is created due to the one-sided excitation of an extended high-frequency discharge supported by a propagating azimuthally symmetric mode of the surface wave. It is shown that a “plasma column” can be an effective plasma antenna at operating frequencies below the plasma frequency (ωp), with frequency tuning due to changes in the length of the “plasma column”.

Excitation and manipulation of toroidal dipole response in an antenna

The toroidal dipole is always overlooked due to its relatively weak interaction with the electromagnetic fields, but it actually exhibits tremendous potential for the design of advanced photonic devices. Here, we demonstrate the existence of toroidal dipole in plasma antenna system, which is rarely observed in the antenna design. It consists of a half-wavelength antenna and eight plasma rings to excite the toroidal dipole to enhance the electromagnetic radiation of the whole antenna system, whose mechanism is different from conventional antenna, which is a multiband antenna. We further confirm that the hybrid mode, which combines the toroidal dipole and multipole moments, can be dynamically adjusted to control both return loss and the opening of operating windows. This allows for flexible tuning of the multiband antenna simply by manipulating the response of the toroidal dipole. Furthermore, the toroidal dipole antenna is stable in dusty plasma, making it suitable for solving the problem of ‘blackout’ phenomena in aerospace communications, which exhibits the additional benefits of reduced cost and easier to manufacture.

Design and Application of High-Density Cold Plasma Devices Based on High Curvature Spiked Tungsten Structured Electrodes

Advances in radar technology have driven efforts to develop effective countermeasures. Plasma is recognized as a highly effective medium for absorbing electromagnetic waves. Recent research has focused on enhancing plasma element performance. This paper achieved ultra-high-density, low-pressure cold plasma with a density of 1.15 × 1012 cm−3, surpassing similar studies by more than an order of magnitude. Tungsten electrodes with high-curvature spiked structures were invented to replace traditional iron–nickel alloy electrodes, increasing plasma density by 88.2% under the same conditions. Lightweight and cost-effective tubular and annular ultra-high-density, low-pressure cold plasma devices were developed, demonstrating exceptional performance in electromagnetic wave absorption, plasma transient antennas, and radar stealth technology. The influence of plasma on electromagnetic waves and its numerical relationship were analyzed. By measuring the radar cross-section (RCS), the reduction in radar detection rates was quantified. The results show that the ultra-high-density cold plasma devices exhibit very low intrinsic RCS values, suitable for plasma antenna applications. The array of plasma elements generates a large-area high-density low-pressure cold plasma. This plasma effectively reduces the radar cross-section (RCS) of metallic equipment in the S and C bands and shows attenuation in the X band. These effects highlight the superior characteristics of plasma technology in electronic warfare. This exploratory research lays the groundwork for further defense applications.

A complete electrode model for plasma impedance probes

Plasma impedance probes measure the impedance spectrum of an antenna immersed in a plasma. The 1964 work of Balmain remains the standard method to interpret these data, using the peak in the magnitude at the upper-hybrid frequency to infer plasma electron density. The primary limitations of Balmain's model are the assumption of a homogenous plasma and a cylindrical dipole. This work presents a numerical model applicable to inhomogeneous plasma and arbitrary antenna geometry based on the cold, fluid approximation given by Balmain. This model solves Poisson's equation using the finite element method and accounts for the effects of the dipole using the plasma complete electrode model (PCEM). The PCEM is developed in this article and accounts for the voltage shunting effects of the dipole elements, the discrete current to the dipole, and the plasma sheath surrounding the dipole. The sheath is incorporated as a contact impedance between the dipole and the plasma in a manner analogous to the complete electrode model of electrical impedance tomography. The first portion of this paper presents the mathematical framework of the PCEM, starting from Maxwell's equations. The second part of the paper compares the output of this numerical method to Balmain's work and to data collected by an impedance probe in the Space Physics Simulation Chamber at the U.S. Naval Research Laboratory. The PCEM results agree with both the observed data and the prior modeling done by Balmain. An additional consequence of the numerical study is the observation that some second-order resonances not predicted by Balmain's model can be attributed to the presence of the plasma sheath.

Influence of Pressure on Plasma Antenna Resonance Wavelength

Influence of Pressure on Plasma Antenna Resonance Wavelength

Effect of the Method of Excitation of the Plasma Antenna on the Spectral Characteristics of the Radiated Signal

Effect of the Method of Excitation of the Plasma Antenna on the Spectral Characteristics of the Radiated Signal

Theory of a Square Loop Antenna in an Anisotropic Magnetized Plasma

Theory of a Square Loop Antenna in an Anisotropic Magnetized Plasma

Wideband frequency reconfigurable plasma antenna launched by surface wave coupler

A wideband reconfigurable plasma antenna excited by a surface wave coupler (SWC) operating at 13.56 MHz is presented in this study. The plasma antenna and SWC are designed and modeled in CST Studio. A detailed analysis of the SWC is carried out using CST Studio, and experimental measurements supplement the performance. This work explores the signal transmission capabilities of a plasma antenna excited at 13.56 MHz for the first time. A SWC is a two-port device that is modified for radiating electromagnetic waves through a plasma column produced at a frequency of 13.56 MHz with a coupling efficiency of 99%. The power port and signal port of the SWC are isolated for better coupling efficiency and to reduce interference. The return loss and isolation between the ports of the SWC at 13.56 MHz are −22 dB and −46.81 dB, respectively. The plasma antenna excited by a surface wave has a wider bandwidth than its metallic counterpart. It varies from 280 to 540 MHz for input plasma power ranging from 2 W to 10 W. In addition, a reconfigurability frequency span of 240 MHz for power ranging from 2 to 10 W is achieved experimentally. Moreover, we attained an enhanced peak gain of -5 dBi. The radiation efficiency of the plasma antenna is around 20%. The experimental results of the SWC and plasma antenna are in coherence with its simulations.

Plasma-activated copper-alkanolamine precursor paste for printed flexible antenna: formulation, mechanism, and performance evaluation

Plasma activation mechanism and antenna application of a printable copper precursor paste were explored, demonstrating its feasibility for use in flexible wireless electronics.

Experimental Characterization and Simulation of a Dipole Plasma Antenna for VHF Band and Effect of Ar–Ne Gas Composition

Experimental Characterization and Simulation of a Dipole Plasma Antenna for VHF Band and Effect of Ar–Ne Gas Composition

Research on plasma devices and antenna systems based on superlattice structures

To decrease the effect of carrier concentration on the skin depth, a new SPiN diode based on superlattice structure is discussed. Compared with traditional plasma diode, the intrinsic region of the SPiN diode is designed with SiGe/Si superlattices layer, and the thickness of the plasma islands is reduced from 80 μm to 5 μm, which dramatically reduced the design complexity and technical difficulty of microwave devices. Besides, a high-integration solid-state plasma inverted-F antenna based on this diode is also demonstrated in this paper. The resonant frequency of the inverted-F plasma antenna is in the order of 2.45 GHz, and the maximum gain reaches to 2 dB, which verify the effectiveness of the designed superlattice SPiN diode.

A Multi-Polarized Reconfigurable Plasma Antenna Array

Research on antenna reconfiguration is important in antenna applications. We present design of a multi-polarized plasma antenna with 40.68 MHz radio frequency (RF) power supplies and several discharge tubes filled with argon (neon) and mercury. Furthermore, self-made regulating circuits among the vibrators are introduced for the antenna array system. It can not only make the length of the dipole controllable but also improve the antenna gain and circular polarization (CP) performance under different lengths. Antenna arrays can be classified into linear and circular polarization by quickly adjusting the phase difference between vibrators. Both the experimental and simulation results indicate that the plasma antenna can realize impedance, pattern, and polarization reconstruction expediently. In addition, the linear polarization (LP) and CP can be transformed into each other quickly by adjusting the discharge conditions and regulating circuits. Moreover, compared with a symmetrical cross vibrator plasma antenna and a metal antenna of the same size, the proposed antenna array shows a certain gain and good reconfigurable performance within the frequency band of 150–250 MHz.

First experimental results of the PAM LHCD launcher at 2.45 GHz on EAST

This paper presents the first results of a passive active multijunction (PAM) launcher at 2.45 GHz during the lower hybrid current drive (LHCD) experiments on EAST. Good coupling performance with a power reflection coefficient (RC) ∼3% has been achieved at the plasma–antenna distance up to ∼11 cm in L-mode edge plasmas without local gas puffing near the PAM launcher. Reliable power coupling of this PAM during the edge perturbations induced by type I edge localized modes (ELMs) has been successfully demonstrated. Compared with the old full active multijunction (FAM) launcher, the new PAM can be placed ∼2 cm further away from the plasma in normal operations, which is in good agreement with the previous prediction (Li et al 2019 Fusion Eng. Des. 147 111 250), by the linear wave–plasma coupling code ALOHA (Hillairet et al 2010 Nucl. Fusion 50 125 010). The flexibility of the power spectrum by changing the phase difference between adjacent modules was validated and ray-tracing/Fokker–Planck simulations can reproduce the experimental features. The achievable power handling is as high as 25 MW m−2, although with a shot pulse length of ∼10 s. The first experiment successfully demonstrated the coupling performance of a PAM launcher at low density and this launcher construction provides helpful engineering experience for the 4.6 GHz PAM development in the near future on EAST.

Analysis of the cylindrical plasma antenna system modes in a wide frequency range

Plasma antennas have promising prospects for practical use with quick changes in their parameters in a wide frequency range. In this work, the radiation pattern of a plasma antenna system, which consists of a short linear antenna surrounded by fluorescent lamps, is analyzed in a frequency range of 0.5–1.5 GHz. In numerical simulation, the parameters of the gas-discharge plasma were used, which were obtained using the drift theory. In addition, an analysis of the radiation patterns using a simple and intuitive ring antenna array model was carried out, and the limit of its applicability was demonstrated. The experimental data were compared with those of simulation and theoretical analysis. Finally, a simulation was performed to compare the plasma antenna system with its metal counterpart. The results obtained are important for a whole class of nested antenna systems.

Fast ion generation by combined RF-NBI heating in W7-X

Good fast ion confinement in quasi-isodynamic stellarators still has to be demonstrated experimentally. In the absence of fusion alphas, auxiliary heating systems can be used to generate fast ions. For this purpose, W7-X has neutral beam injection and its newly installed ion cyclotron heating system. In practice, both systems can run simultaneously, the synergetic running of both is the focus of the current modelling development. With the upgrades to the SCENIC code described here, we find that, compared with pure neutral beam injection (NBI), the fast ion tail is significantly enhanced when radio frequency (RF) heating is enabled. But the effectiveness of heating and fast ion tail generation strongly depends on the plasma parameters and antenna frequency, which calls for further study, both numerical and experimental.

Feasibility study on a plasma based reflective surface for SatCom systems

Gaseous Plasma Antennas (GPAs) exploit an ionized gas to transmit and receive electromagnetic waves. GPAs offer several advantages over metal antennas since, while in use, they are electronically reconfigurable in terms of radiation pattern and operation frequency. When not used, the plasma can be turned “off”, and the GPA reverts to a dielectric tube with a very low radar cross-section. This makes GPAs suitable to be stacked into arrays, providing they can reduce co-site interference. Thus, GPAs are very appealing for Satellite Communications (SatCom). The antenna pointing and tracking obtained by steering the beam electronically, rather than using mechanically moving parts, can enable several space missions. A plasma-based reflective surface has been recently proposed in this framework to maximize reconfigurability. Such a device consists of many plasma discharges placed on top of a metallic ground plane, and the reflection of radio signals can be controlled by electronically varying the plasma properties (e.g., density). This work presents the first step toward practically implementing a plasma-based reflective surface in the X-band capable of electrically, rather than mechanically, tuning its beam steering and focusing capabilities. The study here presented combines numerical and experimental approaches. First, a target plasma discharge has been characterized experimentally to provide the plasma parameters needed to estimate the electromagnetic (EM) response using numerical simulations. Then, the numerical simulations were performed to preliminary design a plasma-based reflective surface. At first, a simplified single-element plasma cylinder was analysed. Then, the glass envelope needed to contain the plasma was added to the column, and its impact on the performance was evaluated. Finally, a finite surface of ten plasma cylinders (including glass vessels) has been considered. The preliminary results prove the capability to obtain beam-steering by tuning the plasma density within the discharges.

Study of the Radiation Pattern and Frequency Response of a Short Linear Antenna Surrounded by Discharge Tubes for the Development of Rapidly Adjustable Wideband Antenna Systems

Plasma antenna systems consisting of discharge elements have great practical application prospects due to their ability to quickly adjust parameters over a wide range. In this work, the radiation patterns of a 30 mm long linear antenna surrounded by 16 standard T8 fluorescent lamps were measured by using a spectrum analyzer with a tracking generator. The radiation pattern of the system is measured by connecting the output of the spectrum analyzer tracking generator to a linear antenna and connecting the input of the spectrum analyzer to the receiving broadband horn antenna. The work features experimental measurements over a wide frequency range of 0.5 to 1.5 GHz and a wide discharge with current values from 35 to 200 mA. The specific frequency band and uniquely selected geometry allowed for the investigation of both the in-phase and out-of-phase antenna modes, while some modes were found to have a narrow directional radiation pattern, within 50 degrees, with a beam width of −3 dB. The parameters of the gas-discharge plasma were also evaluated using drift theory, as well as using the microwave transmission of the 20 GHz signal. The electron density value corresponding to the used discharge currents was approximately from 4 × 1011 to 7 × 1010 cm−3.

Parametric study of midplane gas puffing to maximize ICRF power coupling in ITER

Midplane gas puffing close to the ion cyclotron range of frequencies (ICRF) antennae has been demonstrated to be robust in improving ICRF power coupling in current tokamaks. It is also shown in a previous study (Zhang 2019 Nucl. Mater. Energy 19 364–71) that in ITER, midplane gas puffing with a puff rate of ∼4.5 × 1022 electrons s−1 can increase the antenna loading/coupling resistance by about a factor of two. In this paper, a comprehensive parametric study has been carried out to characterize the influence of midplane gas puffing on ICRF power coupling in additional and broader range of parameter scans. The new parameter scans include the gas puff rate, the poloidal location of the gas pipe orifices (GPOs), the separatrix density, the particle perpendicular diffusion coefficient, the radial distance between the plasma and antenna as well as the antenna phasing. The 3D edge plasma fluid and neutral transport code EMC3-EIRENE code has been used to simulate the 3D distributions of plasma density in the presence of gas puffing, which are then used in the antenna code ANTITER II to calculate the antenna coupling. The simulation results indicate that the ITER ICRF local midplane gas injection layout (with the GPOs located on one side of each antenna port) increases the ICRF power coupling significantly in all studied plasma scenarios and antenna parameters. We are hence confident that the chosen layout for the ICRF local gas injection on ITER is appropriate. We are also confident that the ITER local gas injection will allow boosting the ICRF coupling with all studied plasma conditions and antenna phasings.

Theory of a VLF Circular-Loop Antenna in an Anisotropic Magnetoplasma

The circular-loop antenna is one of the most basic antenna forms for very low frequency (VLF: 3–30 kHz) space-borne transmitting systems. However, the theoretical progress of the loop antenna in an anisotropic plasma is slower than that of the linear antenna due to its complexity. This article studies the theory of a VLF circular-loop antenna located in an anisotropic magnetoplasma. The current integral equation of the current is formulated by deriving the exact kernel function and boundary condition. By taking both the effects of O-wave and E-wave into consideration, the current distribution and input impedance of a circular-loop antenna are solved via the method of moments along with the numerical techniques. The results show that the current amplitude decreases with the loop radius. As the size of the loop increases, the current distribution resembles a cosine function with its phases jumping at several positions. Moreover, the input impedance of the antenna increases as the radius and operating frequency increase. The proposed approach is validated by comparing the computed impedance with that simulated by the commercial software FEKO. The preliminary study of VLF loop antenna theory can offer theoretical guidance in antenna design and efficiency improvement for actual VLF space-borne transmitting systems.