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A gaseous plasma antenna array (PAA) is an aggregate of plasma discharges and possibly conventional metallic radiating elements, and it constitutes a promising alternative to metallic antennas for applications in which fast reconfiguration of radiation pattern, and gain is desired; such properties can be achieved by exploiting the electronic switch on/off condition of plasma discharges, and tuning of the plasma parameters. Here, the authors present a reconfigurable PAA that features a central metallic half-wavelength dipole working around 1.45 GHz, surrounded by a planar circular lattice of cylindrical plasma discharges. Customised plasma discharges have been realised, and filled with argon gas at 2 mbar so as to have a complete control on the plasma discharge properties (e.g. plasma frequency, collisional frequency). The magnitude of the reflection coefficient, and the gain pattern on the H -plane have been investigated numerically and experimentally; numerical and experimental results exhibit a good agreement and show that the central intrinsically omnidirectional antenna can provide simple beamforming capabilities upon turning on a subset of plasma discharges; as these plasma discharges are turned on, the authors have observed a maximum gain of ~5 dBi, a half-power beam width of 80°, and an angular steering resolution of ~15°.

This paper is an extension of the work originally presented at the European Microwave Conference (EuMC) about a reconfigurable hybrid metal-plasma Yagi-Uda antenna operating at 1.55 GHz: this antenna consists of metallic reflector and active element and two plasma directors. The conference work showed through full-wave numerical simulations (CST Microwave Studio) how it is possible to achieve reconfigurability with respect to the gain by turning on/off the plasma discharges. However the model that was used to represent the plasma discharges was quite ideal, so one comment that was provided questioned the actual possibility of achieving reconfigurability in a real system. Consequently we performed extensive measurements of different plasma discharges and thanks to the collected data, we noticed some important differences between the full-wave numerical model of the plasma that we used in the conference paper and the actual plasma discharges that were generated in the experimental setup: the dielectric vessel and the metallic electrodes used respectively to confine and generate the plasma have an influence on the radiation pattern of the antenna and so they must be included in the design procedure; the cylindrical plasma discharge is much easier to realize when the cylinder diameter is at least 3mm; and finally the collision frequency of the plasma in realistic cases is pretty higher than the one adopted in our previous work. Therefore this work presents a feasibility study of a more detailed and realistic model of our antenna with respect to the plasma discharges. We will show that reconfigurability can still be achieved through a proper design of the overall antenna, thus paving the way to an actual realization of the proposed reconfigurable Yagi-Uda.

We have numerically studied how an actual confinement magnetostatic field affects power deposition in a helicon source. We have solved the wave propagation by means of two electromagnetic solvers, namely: (i) plaSma Padova Inhomogeneous Radial Electromagnetic solver (SPIREs), a mono-dimensional finite-difference frequency-domain code, and (ii) Advanced coDe for Anisotropic Media and ANTennas (ADAMANT), a full-wave three-dimensional tool based on the method of moments. We have computed the deposited power spectrum with SPIREs, power deposition profile with ADAMANT and the antenna impedance with both codes. First we have verified the numerical accuracy of both SPIREs and ADAMNT. Then, we have analysed two configurations of magnetostatic field, namely produced by Maxwell coils, and Helmholtz coils. For each configuration we have studied three cases: (i) low density$n=10^{17}~\text{m}^{-3}$and low magnetic field$B_{0}=250$ G; (ii) medium density$n=10^{18}~\text{m}^{-3}$and medium magnetic field$B_{0}=500$ G; (iii) high density$n=10^{19}~\text{m}^{-3}$and high magnetic field$B_{0}=1000$ G. We have found that the Maxwell coil configuration does not produces significant changes in the deposited power phenomenon with respect to a perfectly uniform and axial magnetostatic field. While the Helmholtz coil configuration can lead to a power spectrum peaked near the axis of the discharge.

Since Helicon plasma sources can efficiently couple power and generate high-density plasma, they have received interest also as spacecraft propulsive devices, among other applications. In order to maximize the power deposited into the plasma, it is necessary to assess the performance of the radiofrequency (RF) antenna that drives the discharge, as typical plasma parameters (e.g., the density) are varied. For this reason, we have conducted a comparative analysis of three Helicon sources which feature different RF antennas, namely, the single-loop, the Nagoya Type-III, and the Fractional helix. These antennas are compared in terms of input impedance and induced current density; in particular, the real part of the impedance constitutes a measure of the antenna ability to couple power into the plasma. The results presented in this work have been obtained through a full-wave approach which (being hinged on the numerical solution of a system of integral equations) allows computing the antenna current and impedance self-consistently. Our findings indicate that certain combinations of plasma parameters can indeed maximize the real part of the input impedance and, thus, the deposited power, and that one of the three antennas analyzed performs best for a given plasma. Furthermore, unlike other strategies which rely on approximate antenna models, our approach enables us to reveal that the antenna current density is not spatially uniform, and that a correlation exists between the plasma parameters and the spatial distribution of the current density.

Gaseous plasma antennas are devices that exploit partially or fully ionized gas to transmit and receive electro-magnetic waves, in contrast with conventional antennas that are only made by metal and dielectric materials. Since plasma discharge parameters, e.g. plasma density, can be tuned, plasma antenna properties can be changed dynamically; this constitutes a promising alternative to conventional metallic antennas for applications in which reconfigurability is desired. In this work, we report on the first steps toward the realization, and the characterization in terms of radiation pattern, and magnitude of the reflection coefficient of an early prototype of a gaseous plasma antenna in the UHF frequency range. Numerical investigations have supported the design of the setup, and helped in the evaluation of the the role of plasma density profiles in affecting the antenna properties.

Gaseous plasma antennas constitute a promising alternative to conventional metallic antennas for applications in which reconfigurability is desired. By tuning the plasma discharge parameters, e.g., plasma density, antenna properties can be changed dynamically. In this work we report on recent numerical investigations into the characteristics of a plasma antenna as a function of the plasma discharge parameters, viz., plasma density, and magnetostatic field. In addition, the effect of different gasses has been examined. We have used ADAMANT (Advanced coDe for Anisotropic Media and ANTennas) — a full-wave numerical tool based on integral equations — to assess the role played by plasma discharge parameters in shaping the radiation pattern, which is mainly determined by the plasma current distribution. The experimental characterization of the plasma discharge to be used as plasma antenna is briefly presented.

We present a full-wave numerical tool for the simulation of plasma antennas. The tool makes use of a hybrid formulation that allows treating the plasma with a Finite Element discretization, and the metallic parts with the Method of Moments. The finite element discretization is solved using a state-of-the-art sparse solver (MUMPS) in order to reduce the computational time at a minimum. The accuracy of the tool is tested by comparing the results obtained with it against those obtained with a benchmark code. Finally, a novel dual-mode plasma antenna is designed using the aforementioned tool.

We present the numerical parametric study of a reconfigurable plasma antenna array (PAA) composed of a metallic half-wavelength dipole and a set of cylindrical plasma discharges arranged in a planar square lattice. Our results, obtained with the linear embedding via Green’s operators (LEGO) method, indicate that beam-forming and beam-steering functionality can be achieved and controlled by appropriately choosing the number and position of the active plasma discharges around the dipole. Furthermore, we show that an external static magnetic field and the plasma density have a noticeable effect on the radiation pattern of the antenna.

In this work, a feasibility study of a hybrid metal-plasma Yagi antenna operating at 1.55GHz is presented. In particular, the directors of the antenna are constituted of microplasma discharges that allow to realize very thin and short plasma tubes, thus overcoming some issues related to the use in the GHz regime of classic thick plasma discharges. We will show that this design choice leads to good results in terms of gain with respect to the classic metal Yagi antenna, thus paving the way to a new class of hybrid reconfigurable antennas operating at high frequencies.

Gaseous plasma antenna arrays (PAA) constitute a promising alternative to conventional metallic antennas for applications in which fast reconfigurability with respect to some property (e.g., the gain, the frequency band) is desired. In STARLET (plaSma anTennA foR satelLitE navigaTion) project, reconfigurable capabilities of plasma antennas will be exploited in the design and development of a PAA for the reception of GPS and Galileo satellite signals. Here we give an account of the prelimary numerical results gathered so far.

We present the numerical analysis of a reconfigurable plasma antenna array (PAA) comprised of a metallic half-wavelength dipole and a variable number of cylindrical plasma tubes that are arranged in a planar rectangular lattice. Our simulations, carried out with the linear embedding via Green's operators (LEGO) method, indicate that beam-forming and beam-steering can be realized and controlled by selectively switching the plasma tubes on and off. Moreover, an additional static magnetic field (which makes the plasma non-reciprocal) produces a noticeable rotation of the overall radiation pattern.

Gaseous plasma antenna arrays (PAA) constitute a promising alternative to conventional metallic antennas for applications in which fast reconfigurability with respect to some property (e.g., the directivity) is desired. In this communication we give an account of the ongoing research on PAAs by presenting experimental and numerical results

A plasma antenna is a radiating device partially composed of plasma instead of metals or dielectrics, and as a result, it exhibits reconfigurable properties unlike conventional metallic antennas. By tuning the plasma discharge parameters, e.g., the plasma density, the antenna properties can be changed dynamically. In this work we report on recent numerical investigations into the characteristics of plasma antennas as a function of the plasma discharge parameters. We have used ADAMANT (Advanced coDe for Anisotropic Media and ANTennas) - a full-wave numerical tool based on integral equations - to assess the role played by plasma discharge parameters in shaping the gain function, and the antenna input impedance.

We report the numerical analysis of a plasma antenna array comprised of cylindrical plasma discharges and a conventional half-wavelength metallic dipole. In particular, the 3D radiation pattern, gain and impedance of the antenna are determined and compared for different values of the plasma density. To reduce the computational load by exploiting the translational symmetry of the structure, we have carried out the simulations with the linear embedding via Green's operators (LEGO) method. Our results suggest that the device performs better as a directive antenna at lower plasma densities, that is, when the plasma is less reflective.

In the framework of the ”Helicon Plasma Thruster for Space Missions AO7048” research program, a zero-dimensional numerical model is developed in order to assess the propulsive performances of the plasma thruster when fed with different molecular gases as propellants. The zero-dimensional model developed consists of detailed kinetic schemes for bulk plasma reactions and surface processes; particle in cell simulations are performed to properly describe the behaviour of the charged particles at the exhaust plume so to obtain exhaust parameters for the global model. Given a set of input parameters, such as geometry and mass flow rate, the model is able to follow the time evolution of plasma main physical quantities, such as neutral and charge densities and the electron temperature, and to calculate thruster performances. The model is then linked to the genetic algorithm optimization toolbox in Matlab environment in order to obtain high performance configurations. Propellants considered are H2, O2, N2 and N2O.

In this work we illustrate the design of a thrust balance, to be employed for the experimental characterization of low power helicon plasma thrusters developed at the Center for Aerospace Studies and Activities (CISAS) “G. Colombo” of the University of Padua. The nominal thrust level of the propulsive systems to be tested is estimated between 1 and 20 mN. The measurement of millinewton-range thrusts in presence of RF emissions magnetic fields from the thruster poses several engineering challenges as: (i) an highly sensible system is required, capable of detecting the low thrust levels produced by the thrusters with sufficient accuracy and stability; (ii) the necessity of feeding RF power to the thruster mounted on the balance imposes to deal with RF disturbances on the measurement systems and RF heating of the power line and of the mechanical structure of the balance; (iii) the magnetic field can interact with elements of the balance, hampering the measurement. We considered all these aspects with careful theoretical analyses, supported by experimental validation of the envisioned solutions. The work was thus structured as follow: (i) definition of the physical principles related to the measurement of millinewton-range thrusts in an RF environment; (ii) definition and preliminary characterization of the mechanical configuration of the system; (iii) definition of the measurement chain, in terms of mechanical interfaces, sensors, RF shielding and data handling, (iv) analysis of system criticalities; (v) design and experimental validation of the critical technologies involved in the system; (vi) detailed design of the thrust balance.

Radiofrequency (RF) magnetized Helicon plasma sources have been proposed for the development of space thrusters, whose thrust efficiency and specific impulse depend on the power coupled into the plasma by the RF antenna that drives the discharge. In this work we report on a set of numerical experiments specifically conceived to optimize Helicon sources in terms of plasma parameters (e.g., gas species, plasma density, external magnetostatic field, neutral pressure), and the RF antenna shape. Results concerning the power coupled into the plasma and the antenna impedance for different antenna configurations and plasma parameters are presented and discussed.

We present a full-wave numerical tool, dubbed ADAMANT (Advanced coDe for Anisotropic Media and ANTennas), devised for the analysis and design of radiofrequency antennas which drive the discharge in helicon plasma sources. ADAMANT relies on a set of coupled surface and volume integral equations in which the unknowns are the surface electric current density on the antenna conductors and the volume polarization current within the plasma. The latter can be inhomogeneous and anisotropic whereas the antenna can have arbitrary shape. The set of integral equations is solved numerically through the Method of Moments with sub-sectional surface and volume vector basis functions. This approach allows the accurate evaluation of the current distribution on the antenna and in the plasma as well as the antenna input impedance, a parameter crucial for the design of the feeding and matching network. We report several numerical examples which serve to validate ADAMANT against other well-established numerical approaches as well as experimental data. The numerical accuracy of the computed solution versus the number of basis functions in the plasma is also assessed. Finally, we employ ADAMANT to characterize the antenna of a real-life helicon plasma source.

Linear embedding via Green’s operators (LEGO) is a domain decomposition method in which complex radiation and scattering problems are modelled and solved by means of interacting electromagnetic "bricks". We propose an extension of LEGO able to handle bodies with anisotropic constitutive parameters and metallic objects (e.g., antennas). Since the anisotropic objects are dealt with LEGO, and the metallic parts are treated with the electric field integral equation (EFIE), we refer to the overall approach as hybrid LEGO-EFIE. The characterization of an electromagnetic brick which embeds an anisotropic object requires solving a volume integral equation (VIE). Since this procedure is carried out for each brick independently, the LEGO approach per se is extremely advantageous over the direct solution of a global VIE for all the bodies at once. Nonetheless, we further mix the hybrid LEGO-EFIE approach with the eigencurrents expansion method in order to tackle relatively larger problems. The technique is used to analyze a reconfigurable plasma antenna array (PAA) comprised of magnetized-plasma tubes placed around a two-dipole antenna array.

Radiofrequency (RF) magnetized Helicon plasma sources have been proposed as propulsive devices for space thrusters. In order to optimize the antenna-plasma coupling in a Helicon source the ADAMANT code, which implements the numerical solution of surface-volume integral equations, has been developed; the approach lends itself to parallel execution. Results concerning the speed-up obtained through parallelization will be discussed.

The optimization of radiofrequency magnetized plasma sources for space thrusters has focused on power deposition in nonuniform plasmas. However, many researchers assumed rather than computed the induced current density on the antenna, and considered a uniform and constant magneto-static field aligned with the source axis. To overcome these limitations, we propose two methods: (i) a full-wave approach to compute the current distribution on the antenna and (ii) a ray-tracing approach to investigate the influence of actual magneto-static fields on the wave propagation and power deposition. Plasma density profiles are included in both approaches. In the full-wave method, we derive a surface integral equation for the antenna and a volume integral equation for the plasma by applying the electromagnetic equivalence principles. A comparative study of different antennas will be presented. In the second method, the propagation and absorption of electromagnetic waves are investigated by solving the 3D Maxwell-Vlasov model equations by a WKB asymptotic expansion. Unconventional mode conversions and power deposition profiles are found when realistic confinement magnetic field are considered.

Optimization of radiofrequency helicon plasma sources for the development of space plasma thrusters (whose thrust efficiency and specific impulse depend on the power coupled into the plasma) has focused on the absorption of wave energy by cold collisional plasmas, but not much on the role played by the antenna that drives the discharge. To overcome these limitations and to optimize the power deposited by the antenna into the plasma, we propose a full-wave approach based on integral equations to compute the current distribution on the antenna conductors self-consistently, i.e., also keeping into account the effect that the plasma in turn has on the antenna. Preliminary results of antenna current distribution and antenna impedance versus frequency and plasma parameters are presented.

Satellite communication systems have demonstrated their essential role providing timely services for disaster management in a variety of distress situations. Their effectiveness requires high mapping and pointing accuracy in terms of displacement capability, and high gain, high bandwidth, directional, and reconfigurable antennas in terms of communication capability. A Helicon plasma thruster, and an enhanced communication system meet the aforementioned requirements. The former is an electric plasma-based propulsion system that provides an high accuracy attitude control, while the latter could be either an optimized state-of-the-art antenna or an innovative concept based on plasma antennas. In this research work, several computationally efficient codes have been developed to analyze, design and optimize the helicon plasma thruster, and the antenna for an enhanced communication system. The present work progresses starting from the definition of the requisites, and continues to describe the innovative numerical methods: the SPIREs finite-difference frequency-domain electromagnetic solver for magnetized plasma cylinders; the WAVEQM equilibrium condition solver for radiofrequency heated plasmas; the PARTYWAVE particle in cell code for cylindrical geometries, and the Moment Method for antenna design. Their numerical accuracy has been verified, and they have been validated against physical cases.

The physics involved in the coupling, propagation and absorption of RF helicon waves (electronic whistler) in low temperature Helicon plasma sources is investigated by solving the 3D Maxwell-Vlasov model equations using a WKB asymptotic expansion. The reduced set of equations is formally Hamiltonian and allows for the reconstruction of the wave front of the propagating wave, monitoring along the calculation that the WKB expansion remains satisfied. This method can be fruitfully employed in a new investigation of the power deposition mechanisms involved in common Helicon low temperature plasma sources when a general confinement magnetic field configuration is allowed, unveiling new physical insight in the wave propagation and absorption phenomena and stimulating further research for the design of innovative and more efficient low temperature plasma sources. A brief overview of this methodology and its capabilities has been presented in this paper.

Current electric propulsion technology is based on families of thrusters able to cope efficiently with different mission profiles. However, they are not versatile enough to allow a unique propulsion system technology for the entire mission. Helicon –source-based plasma thrusters promise to bea very versatile family of systems, able to be adaptedto very different mission configurations with a substantial reduction in costs and increase in reliability. However, their development is mainly confined in theUS and Japan. Moreover, although helicon plasma sources have been proved to be very efficient, theirfundamental physical mechanisms need still to be investigated. The Helicon Plasma Hydrazine.Combined Micro (HPH.com) is a research project funded by the European Committee within the 7th Framework Programme of the EU and conducted by an international consortium. Objective of this research is to significantly improve knowledge on helicon-based plasma thrusters through deep numerical/theoretical investigations and extensive experimental campaigns, and then to apply the results to the design, optimization and development of a space plasma thruster. The thruster will be specifically conceived to be used on board a mini-satellite for attitude and position control in order to allow low-cost demonstration mission. Finally, to further increase versatility of this system, far beyond that of a standard electric thruster, a detailed feasibility study will be also conducted to evaluate the possibility of using plasmas to heat and or decompose a secondary propellant, in order to develop a two-mode system, high-efficiency low-thrust plasma-thruster mode and a low-efficiency high-trust secondarypropellant- plasma–enhanced mode. In the following a general overview of the HPH.com research project and a description of the current project status are presented.

This paper is focused on the description of simulation codes developed to design a helicon plasma thruster for a small satellite under development in the research project Helicon plasma hydrazine combined micro (HPH.com) conducted within the 7th Framework Program of the EU by a European consortium.

Radiofrequency magnetized cylindrical plasma sources are proposed for the development of space thrusters, whose thrust efficiency and specific impulse depend on the power coupled into the plasma. At this stage of research, emphasis has been on the absorption of Whistler wave energy by non-uniform plasmas but not much on the role played by the magneto-static confinement field, considered uniform, constant and aligned with the axis of the source. We present RAYWh (RAY-tracing Whistler), a three-dimensional (3D) ray-tracing solver for electromagnetic propagation and power deposition in cylindrical plasma sources for space plasma thrusters, where actual magnetic confinement configurations along with plasma density profiles are included. The propagation and absorption of Whistler waves are investigated by solving the 3D Maxwell-Vlasov model equations by a Wentzel-Kramers-Brillouin (WKB) asymptotic expansion. The reduced set of equations for the wave phase and for the square amplitude of the electric field is solved numerically by means of a modified Runge-Kutta algorithm. Unexpected cut-offs, resonances, radial reflections, mode conversions and power deposition profile of the excited waves are found, when realistic confinement magnetic fields are considered. An analysis of the influence of axial wavenumbers and the axial length of the system on the power deposition is presented. © 2014 IOP Publishing Ltd.

We have designed and tested a thrust stand conceived for the characterization of RF plasma thrusters. The balance has been employed in the development of small-medium size HPT prototypes, therefore it allows for an high number of tests per day with an accuracy within the 10%. The balance relies on the counterbalanced-type pendulum concept, which allows to achieve high sensitivity while maintaining a low overall size of the system; the displacement is measured by means of an high-accuracy laser interferometer put outside the vacuum chamber. The system can be calibrated with both a calibration mass, before the test, and an electro-magnetic device, during the test session. We have verified the linear behavior of the instrument and we have developed a dedicated algorithm in order to correct the thermal drifts of the balance. We have compared the stand measurements with the thrust estimations derived from Faraday probe measurements within the plasma plume, verifying that the two estimates are in agreement within 20%.