Loop Antenna Research Articles

Whistler wave radiation from a circular phased array of filamentary loop antennas immersed in a homogeneous cold collisionless magnetoplasma is studied. The array axis is aligned with an external static magnetic field superimposed on the plasma, and the loop axes are assumed to be tangential to the array circumference. An exact solution is obtained for the field excited by the array. Its total radiated power and partial powers going to different azimuthal field harmonics are determined. Numerical results are presented for these radiation characteristics in the whistler frequency range under conditions of the Earth's ionosphere. The results for such an array are compared with those obtained earlier in the case where the axes of the loop antennas are parallel to the external magnetic field. It is concluded that the considered phased array is capable of selectively exciting twisted whistler waves with the desired azimuthal indices and can be used as an efficient source of such waves in a magnetoplasma.

A terahertz multiband metamaterial based rectangular loop antenna with 2×2 split ring resonator arrays and photonic band gap structures

The continuous-wave (CW) illuminator, whose fundamentals are related to the theoretical understanding of loop antennas loaded with ferrite materials, is a device which plays an important role in electromagnetic pulse (EMP) susceptibility assessment. However, existing theoretical formulas do not consider cases where ferrite materials are loaded into the loop antenna. This paper provides a new explicit theoretical formula for the impedance of a circular loop antenna loaded with ferrite materials for CW illuminator design, and explores the variation regularity of its input impedance. Loading ferrite materials affects the internal impedance of the loop antenna and forces some modifications to the classical calculation procedure, resulting in an asymptotic numerical calculation method and a closed-form solution. The full-wave simulation results from CST Studio Suite show a maximum error of less than 0.99%, compared to the classical theory. With ferrite material loaded, the input impedance of the loop antenna is significantly reduced and smoothed in a wide range of normalized radii. For a loop antenna with a fixed circumference, the input impedance indicates that the Q-factor decreases as the thickness of the ferrite material increases. Conversely, for a ferrite-loaded loop antenna with a constant material thickness, a larger loop circumference results in a higher Q-factor. In summary, this study provides a fast and accurate computational method for the input impedance design of CW illuminators, while also offering an effective tool for further research on the performance of ferrite-loaded loop antennas.

Active removal of space debris is an emerging technology aimed at sustaining space activity in Earth orbit by mitigating the risk of collisions between operational satellites and debris. Utilizing a bi-directional magnetic nozzle (MN) radiofrequency (rf) plasma thruster has been proposed to remediate and remove debris from the Earth orbit, where the debris is decelerated by continuously exerting a force to the debris by a plasma beam ejected from the thruster, and zero net force exerted to the thruster is simultaneously maintained by ejecting a second plasma beam to the opposite direction, maintaining the distance between the satellite and the debris. Previous laboratory experiment has demonstrated bi-directional plasma ejection from a single MN rf plasma thruster having two open source exits for symmetric magnetic field configuration having fairly straight magnetic field lines in the insulator source tube wound by a rf loop antenna. Enhancing the force exerted on the debris is essential for reducing the time required for deorbiting. Here it is demonstrated that a symmetric cusp-field configuration can increase the force exerted to the debris under the circumstance that the thrust is maintained at nearly zero level by the bi-directional ejection of the plasma, where the convergent-divergent MNs are formed near the two open-source exits.

This paper presents an analytical model for electromagnetic fields radiated from a circular loop (CL) antenna with an arbitrary current and dimensions placed horizontally over a homogeneous lossy half-space. The analysis is based on the application of the image theory and the reflection coefficient (RC) approximation approach. This method makes it much easier to evaluate the field components radiated from the antenna with quite adequate precision than the Sommerfeld integral technique, which involves the evaluation of improper integrals by numerical methods. The generic field formulas presented in the study are used to derive the axial fields, far fields, and the fields of a uniform current CL antenna over a lossy half-space as special cases. The results obtained with the proposed model for dry earth, moist earth and sea water are in good agreement with the corresponding results from FEKO simulation software, provided that the loop is operating at or near its resonant frequency and that its height above the lossy half space is greater than a tenth of the resonant wavelength.

Abstract This study presents a validated design of a dual‐band wireless relay system of “pucks” for through‐ice communication between a cryobot and a surface lander during a future exploration of the Europan cryosphere. The design of a terrestrial demonstration system and the results of a 103 m through‐ice system test in a relevant environment near Longyearbyen, Svalbard are presented. A radiative transfer model of the Europan cryosphere is applied to evaluate the anticipated performance of the notional Europan relay system. The proposed relay communication system utilizes a circularly polarized patch antenna with dielectric cover layer for use in an upper UHF band, and a crossed ferrite‐loaded loop antenna for use in a lower HF band. A sub‐surface radiative transfer model for Europa is used to extrapolate the performance of the terrestrial demonstration system in the cryogenic outer conductive and mushy inner convective cryosphere layers. The extrapolation considers the number of pucks and deployment strategy required to achieve reliable communication with the cryobot at the sub‐surface ocean interface and the size, weight, and power (SWaP) requirements of those pucks. It is found that the link budgets of the puck pairs is attenuation dominated and highly affected by Europan ice salt fraction. The UHF/HF puck system is found to be suitable within the outer conductive cryosphere, but the SWaP of a UHF/HF puck system used to penetrate the inner convective cryosphere is high enough to warrant use of complementary communication methods.

Precise timing synchronization remains a fundamental requirement for modern navigation and communication systems, where the miniaturization of Loran-C infrastructure presents both technical challenges and practical significance. Conventional miniaturized loop antennas cannot simultaneously meet the requirements of the Loran-C signal for both radiation intensity and bandwidth due to inherent quality factor (Q) limitations. A sub-cubic-meter impedance matching (IM) antenna is proposed, featuring a −20 dB bandwidth of 18 kHz and over 7-fold radiation enhancement. The proposed design leverages a planar-transformer-based impedance matching network to enable efficient 100 kHz operation in a compact form factor, while a resonant coil structure is adopted at the receiver side to enhance the system’s sensitivity. The miniaturized Loran-C timing system incorporating the IM antenna achieves an extended decoding range of >100 m with merely 100 W input power, exceeding conventional loop antennas limited to 30 m operation. This design successfully achieves overall miniaturization of the Loran-C timing system while breaking through the current transmission distance limitations of compact antennas, extending the effective transmission range to the hundred-meter scale. The design provides a case for developing compact yet high-performance Loran-C systems.

This paper presents a dual-band aperture-shared planar antenna for ISM applications, operating at 2.45 and 5.8 GHz. It integrates a rectangular dielectric resonator antenna (RDRA) with a cross-slot feed and circular patch for circular polarization and high gain in the upper band, achieving a broadside gain of 10.05 dBi and 4.15% axial ratio bandwidth. A modified Alford loop antenna in the lower band provides a gain of 2.3 dBi and 14.1% impedance bandwidth. Simulations and measurements confirm performance with over 20 dB port isolation. Compared to existing designs, it offers superior pattern/polarization diversity, bandwidth, and gain in a compact form factor, suitable for modern wireless systems.

In order to break through the difficulties with a very-low-frequency (VLF) miniaturized antenna with small power capacity and low radiation efficiency, this paper proposes a high-radiation-field-strength magnetic loop antenna based on a nanocrystalline alloy magnetic core. A high-permeability nanocrystalline toroidal core (μr = 50,000, Bs = 1.2 T) is used to optimize the thickness-to-diameter ratio (t = 0.08) and increase the effective permeability to 11,000. The Leeds wires, characterized by their substantial carrying capacity, are manufactured through a toroidal winding process. This method results in a 68% reduction in leakage compared to traditional radial winding techniques and enhances magnetic induction strength by a factor of 1.5. Additionally, this approach effectively minimizes losses, thereby facilitating support for kilowatt-level power inputs. A cascaded LC resonant network (resonant capacitance 2.3 μF) and ferrite balun transformer (power capacity 3.37 kW) realize a 20-times amplification of the input current. A series connection of a high-voltage isolation capacitor blocks DC bias noise, guaranteeing the stable transmission of 1200 W power, which is 6 times higher than the power capacity of traditional ring antenna. At 7.8 kHz frequency, the magnetic field strength at 120 m reaches 47.32 dBμA/m, and, if 0.16 pT is used as the threshold, the communication distance can reach 1446 m, which is significantly better than the traditional solution. This design marks the first instance of achieving kilowatt-class VLF effective radiation in a compact 51 cm-diameter magnetic loop antenna, offering a highly efficient solution for applications such as mine communication and geological exploration.

A reconfigurable loop antenna with a coupling window is designed to achieve a wideband performance for the requirement of 5G transceiver applications at n7 (2450–2690 MHz) and n48 (3550–3700 MHz) bands. Initially, a coupling window has been designed for the improvement of the proposed antenna’s bandwidth. Later, three trap circuits are introduced to adjust the original impedance of the proposed antenna at the initial stage. Later, a comprehensive parametric study was performed to determine the influence of each trap circuit that has been included on the antenna surface for reconfigurable function. Then, a modified Genetic Algorithm by HFSS combined with MATLAB through a visual script is applied to optimize the impedance matching under the requirement of S11< -10 dB in n7 and n48 bands. Finally, the optimized physical antenna was constructed and tested by using a Vector Network Analyzer (VNA) in the open site to verify the optimized simulation results. Radiation patterns of the proposed antenna are analyzed in the anechoic chamber to understand the radiation characteristics of the proposed antenna in E-planes and H-planes. The measurement of the proposed reconfigurable loop antenna validates that it has a very wideband covering from 2450 to 3700 MHz, and its gain can achieve 5G requirements in both n7 (2450–2690 MHz) and n48 (3550–3700 MHz) bands.

We study the large-scale co-evolution of the system of currents, magnetic fields, and density perturbations arising from pulsed rf plasma heating using a loop antenna in the experiments at the Krot plasma device. Localized heating of electrons by a short rf pulse leads to redistribution of magnetized plasma particles in a fast, so-called unipolar (non-ambipolar) regime, which is accompanied by the excitation of eddy electric currents [Aidakina et al., “Experimental demonstration of the “unipolar cell” dynamics in a large laboratory magnetoplasma,” Phys. Plasmas 31, 122110 (2024)]. The pulsed currents generated in the plasma can propagate over large distances from the source in the form of low-frequency waves. It is shown that the parallel transport of the currents and magnetic field perturbations occurs at the velocity of whistler waves, whose dispersion is determined by the characteristic time of electron heating, i.e., the duration of the rf pulse and its edges. The perpendicular dynamics of the currents and magnetic fields in a dense and collisional plasma is diffusive due to the finite conductivity determined by Coulomb collisions. Density perturbations arising from electron heating propagate at significantly lower (ion sound) velocities. The experiments performed demonstrate the possibility of nonlinear generation of pulsed whistlers using a compact antenna excited by a short rf pulse.

ABSTRACTA compact high‐gain endfire loop antenna array based on a double‐sided parallel stripline (DSPSL) structure is proposed in this letter. The proposed design achieves radiation mode transformation by deforming the DSPSL into two half‐loops positioned on opposite sides of the substrate. A single feed port is employed, while the other port is terminated with a metal pin for impedance matching. By integrating a parasitic circular patch within the loop structure, the design effectively suppresses sidelobes and significantly enhances directionality. Furthermore, the endfire gain is further improved by incorporating a reflector behind the first radiating element. A prototype was fabricated and measured, demonstrating excellent agreement between simulated and experimental results. The measured peak gain reaches 13.57 dBi within the operating bandwidth, while maintaining a compact overall volume of only 0.19.

Surface Discharge Detection with Ultra High Frequency Loop Antenna Sensor

рассматривается конструкция рамочной антенны с дипольными излучателями, разработанная на основе классической рамочной антенны. Данная антенная система способна эффективно работать на двух частотах: 140 МГц и 390 МГц, что делает ее применимой для широкого круга задач, включая системы связи и радиомониторинга. Для анализа характеристик антенны было проведено компьютерное моделирование с использованием высокопроизводительного программного пакета CST Studio Suite. Это позволило детально изучить электродинамические параметры антенны, такие как диаграмма направленности, входное сопротивление и частотные характеристики. Для подтверждения результатов моделирования был изготовлен физический макет антенны, после чего проведены его экспериментальные исследования. Измерения показали, что коэффициент полезного действия (КПД) антенны составляет минус 0.42 дБ, а коэффициент направленного действия (КНД) достигает 2.26 дБ. Сравнение данных, полученных в результате моделирования и эксперимента, продемонстрировало их высокую степень совпадения, что подтверждает точность проведенных расчетов и измерений. Полученные результаты свидетельствуют о том, что предложенная конструкция антенны обладает стабильными характеристиками и может быть успешно использована в практических приложениях. Подчеркивается важность комплексного подхода, включающего как численное моделирование, так и экспериментальные исследования, для разработки и оптимизации современных антенных систем the paper considers the design of a loop antenna with dipole radiators, developed on the basis of a classic loop antenna. This antenna system can effectively operate at two frequencies: 140 MHz and 390 MHz, which makes it applicable for a wide range of tasks, including communication systems and radio monitoring. To analyze the antenna characteristics, we performed computer modeling using the high-performance CST Studio Suite software package. This made it possible to study in detail the electrodynamic parameters of the antenna, such as the radiation pattern, input impedance and frequency characteristics. To confirm the modeling results, we made a physical model of the antenna, after which we studied it experimentally. Measurements showed that the efficiency of the antenna is -0.42 dB, and the directivity coefficient (DC) reaches 2.26 dB. Comparison of the data obtained as a result of modeling and experiment demonstrated their high degree of coincidence, which confirms the accuracy of the calculations and measurements. The obtained results indicate that the proposed antenna design has stable characteristics and can be successfully used in practical applications. The work emphasizes the importance of an integrated approach, including both numerical modeling and experimental studies, for the development and optimization of modern antenna systems

Abstract This article presents the physics for determining an appropriate helicon plasma source for the Linear Experimental Advanced Device (LEAD) through tripartite mutual verification encompassing theoretical analysis, code simulation, and experimental validation. Using the HELIC code, plasma excitation processes were simulated employing three antenna configurations: m = 1 half-helix, m = 1 Boswell, and m = 0 single-loop helicon antennas, complemented by theoretical interpretations. Key parameters including plasma impedance (Rp ) and energy deposition profiles along radial (Pr ) and axial (Pz ) directions were comparatively analyzed, revealing significantly enhanced Rp , Pr , and Pz values for the loop antenna configuration. Wave propagation equation solutions predicted a primary plasma generation layer at the antenna center, while numerical simulations identified an additional plasma formation region at the antenna boundary, indicative of edge Landau damping effects. Notably, our findings demonstrate that stronger axial magnetic fields do not necessarily correlate with higher plasma densities, particularly for m = 0 antenna configurations. Experimental validation conducted with an m = 0 multi-loop plasma source confirmed these findings. Both theoretical analyses and experimental studies on large-volume plasma generation utilizing this innovative source elucidated the underlying mechanisms responsible for the remarkable low mode transition threshold of 150-watt input power and demonstrated significantly enhanced plasma confinement properties.

Eco-Friendly Circular Meandered Loop Antenna Design Based on Novel PLA/PHBV Biocomposite and SWCNT Conductive Material for Medical Applications

Mutual Coupling Correction Factor for Optimized Multiaxis Shielded Loop Antenna Magnetic Field Measurements

This paper presents a study on the repeatability of washing effects on two antenna-based sensors for breathing monitoring. One sensor is an embroidered meander antenna-based sensor integrated into a T-shirt, and the other is a loop antenna integrated into a belt. Both sensors were subjected to five washing cycles, and their performance was assessed after each wash. The embroidered meander antenna was specifically compared before and after washing to monitor a male volunteer’s different breathing patterns, that is, eupnea, apnea, hypopnea, and hyperpnea. Stretching tests were also conducted to evaluate the impact of mechanical deformation on sensor behavior. The results highlight the changes in sensor performance across multiple washes and stretching conditions, offering insights into the durability and reliability of these embroidered and loop antennas for practical applications in wearable health monitoring. The findings emphasize the importance of considering both washing and mechanical stress in the design of robust antenna-based sensors.

In this paper, the uplink spectral efficiency performance of a massive MIMO system based on full-duplex relay communication is investigated in Rician fading channels. The relay station is equipped with a large number of antennas, while multiple source and destination nodes are located at both ends of the transceiver. Each source and destination node is equipped with a single antenna. The relay station adopts Maximum Ratio Combining/Maximum Ratio Transmission (MRC/MRT) and Equal Gain Combining/Equal Gain Transmission (EGC/EGT) schemes to perform linear preprocessing on the received signals. Approximate expressions for uplink spectral efficiency under both MRC/MRT and EGC/EGT schemes are derived, and the effects of antenna number, signal-to-noise ratio (SNR), and loop interference on spectral efficiency are analyzed. In addition, the impact of full-duplex and half-duplex modes on system performance is compared, and a hybrid relay scheme is proposed to maximize the total spectral efficiency by dynamically switching between full-duplex and half-duplex modes based on varying levels of loop interference. Finally, a novel power allocation scheme is proposed to maximize energy efficiency under given total spectral efficiency and peak power constraints at both the relay and source nodes. The results show that the impact of loop interference can be eliminated by using a massive receive antenna array, leading to the disappearance of inter-pair interference and noise. Under these conditions, the spectral efficiency of the system can be improved up to 2N times, while the transmission power of the user and relay nodes can be reduced to 1/Nrx and 1/Ntx, respectively.

The ferrite loop antenna has been universally employed in the low- and medium-frequency regions of the radio spectrum. It is immune to electrostatic noise and gives satisfactory performance in a small size. Ferrite cores have been available in two popular shapes, cylindrical rod and rectangular slab, for use in amplitude modulation (AM) radio receivers. The ferrite loop antenna has many interdependent parameters and an attempt has been made for its approximate analysis. The performance of a magnetic loop antenna may be improved upon with modification in the geometry of the core, as well as stacking of the cores available off the shelf. Some of the core stacking configurations have been analyzed and compared here.