Search Results (56)

Ultra-wideband (UWB) technology is a crucial facilitator for high-data-rate wireless communication due to its extensive frequency spectrum and low power consumption. Simultaneously, multiple-input multiple-output (MIMO) systems have garnered considerable attention owing to their capability to enhance channel capacity and link dependability. This article discusses the development of small, high-performance MIMO UWB antennas with mutual suppression capabilities to fully use the benefits of both technologies. Additionally, the suggested antenna features a straightforward design and dual-band-notched characteristics. The antenna structure includes two radiating elements measuring 85 × 45 mm². These elements use a rectangular patch provided by a coplanar waveguide (CPW). Double U-shaped slots are incorporated into the rectangular patch to introduce dual-band-notched properties, which help mitigate interference from WiMAX and WLAN communication systems. The antenna is fabricated on a Mylar^® polyester film substrate of 0.3 mm in thickness, with a dielectric constant of 3.2. According to the measurement results, the suggested antenna functions efficiently across the frequency spectrum of 2.29 to 20 GHz, with excellent impedance matching throughout the bandwidth. Furthermore, it provides dual-band-notched coverage at 3.08–3.8 GHz for WiMAX and 4.98–5.89 GHz for WLAN. The antenna exhibits impressive performance, including favorable radiation attributes, consistent gain, and little mutual coupling (less than −20 dB). Additionally, the envelope correlation coefficient (ECC) is extremely low (ECC < 0.01) across the working bandwidth, which indicates excellent UWB MIMO performance. This paper offers an appropriate design methodology for future flexible and compact UWB MIMO systems that can serve as interference-resilient antennas for next-generation wireless applications. Full article

Accurate path-loss characterization in the upper mid-band is critical for 5G/6G outdoor planning, yet classical deterministic expressions lose fidelity at 18 GHz, and purely data-driven regressors offer limited physical insight. We present a physics-guided residual learner that couples a calibrated two-ray model with an XGBoost regressor trained on the deterministic residuals. To enlarge the feature space without promoting overfitting, synthetic samples obtained by perturbing antenna height and ground permittivity within realistic bounds are introduced with a weight of $w=0.3$. The methodology is validated with narrowband measurements collected along two straight 25 m corridors. Under cross-corridor transfer, the hybrid predictor attains $0.59$–$0.62$ dB RMSE and $R^2\ge 0.996$, reducing the error of a pure-ML baseline by half and surpassing deterministic formulas by a factor of four. Small-scale analysis yields decorrelation lengths of 0.23 m and 0.41 m; a cross-correlation peak of unity at $\Delta =0.10$ m confirms the physical coherence of both corridors. We achieve <1 dB error using a small set of field measurements plus simple synthetic data. The method keeps a clear mathematical core and can be extended to other priors, NLOS cases, and semi-open hotspots. Full article

This work presents the use of a novel impedance coupling technique and electrical length increase by using stub loading placed from the radiator to the ground plane. This method is applied to the design of a small four-element ultrawideband (UWB) MIMO antenna arranged in axial symmetry to achieve a compact array size while obtaining a bandwidth starting from a very low cutoff frequency compared to a conventional radiator operating at the same frequency. The four-element MIMO antenna, with an operational bandwidth of 1.9 GHz to 30 GHz, is based on a wideband monopole with a semicircular geometry, fed by a coplanar structure and an L-shaped half-ground plane section. To increase the electrical length of the structure and achieve a compact antenna design, reactive stub loading is introduced, placing it on the backside of the substrate, located orthogonally between the radiator and the L-shaped ground plane, obtaining a small-sized configuration. The axial symmetry is employed to increase the antennas’ isolation by taking advantage of the orthogonal positioning and making the radiated fields have a low correlation. The antenna array footprint measures 48 mm × 48 mm, corresponding to 0.3λ₀ × 0.3λ₀ at the lower cutoff frequency. The array exhibits a low envelope correlation coefficient (ECC) of around 0.033 at 2 GHz, and less than 0.001 at the rest of the bandwidth; a diversity gain (DG) of approximately 10; a stable total active reflection coefficient (TARC) below −10 dB; interport isolation between 20 and 40 dB; and an average gain of 2.8 dBi. Full article

In this paper, we establish criteria for the design of small aperture antenna arrays for Direction of Arrival (DOA) estimation. We define a small aperture antenna array as one consisting of a few elements with an average interelement spacing less than or equal to half a wavelength. We use the spatial covariance matrix of the antenna array to derive the design criterion. It is well known that the DOA estimation performance of an antenna array is strongly related to the amount of information in this matrix. Also, the Cramer-Rao Bound of the estimated DOA is closely related to this matrix. We establish and demonstrate that, for optimal DOA estimation performance, a small aperture antenna array should have non-uniformly spaced and dissimilar antenna elements. Since mutual coupling between antenna elements makes their in situ responses dissimilar, instead of mitigating mutual coupling, one should include mutual coupling in the DOA estimation process to enhance the DOA estimation performance of antenna arrays. Full article

Multiple-input–multiple-output (MIMO), which uses multiple antennas at the transmitter and receiver, is now an essential technique for increasing communication capacity without widening the occupied radio bandwidth. However, antenna arrays within a deep subwavelength dimension degrade MIMO performance due to mutual coupling between the antenna elements. In particular, very small devices such as smartwatches encounter this problem. To address this, we propose Augmented MIMO, mounting a larger antenna array on the human body, for small wearable devices. The experimental results demonstrate throughput improvement with the proposed scheme, even if the overall antenna gain decreases with external body-mounted antennas. This work contributes to the future development of yet another scheme to improve the communication performance of small wearable devices—using the human body as a spacious antenna fixture. Full article

This paper presents a comprehensive survey of state-of-the-art UAV–based antennas and propagation measurements. Unmanned aerial vehicles (UAVs) have emerged as powerful tools for in situ electromagnetic field assessments due to their flexibility, cost-effectiveness, and ability to operate in challenging environments. This paper highlights various UAV applications, from testing large–scale antenna arrays, such as those used in the square kilometer array (SKA), to evaluating channel models for 5G/6G networks. Additionally, the review discusses technical challenges, such as positioning accuracy and antenna alignment, and it provides insights into the latest advancements in portable measurement systems and antenna designs tailored for UAV use. During the UAV–based antenna measurements, key contributors to the relatively small inaccuracies of around 0.5 to 1 dB are identified. In addition to factors such as GPS positioning errors and UAV vibrations, ground reflections can significantly contribute to inaccuracies, leading to variations in the measured radiation patterns of the antenna. By minimizing ground reflections during UAV–based antenna measurements, errors in key measured antenna parameters, such as HPBW, realized gain, and the front-to-back ratio, can be effectively mitigated. To understand the source of propagation losses in a UAV to ground link, simulations were conducted in CST. These simulations identified scattering effects caused by surrounding buildings. Additionally, by simulating a UAV with a horn antenna, potential sources of electromagnetic coupling between the antenna and the UAV body were detected. The survey concludes by identifying key areas for future research and emphasizing the potential of UAVs to revolutionize antenna and propagation measurement practices to avoid the inaccuracies of the antenna parameters measured by the UAV. Full article

The emission rate of atom-like photon sources can be significantly improved by coupling them to plasmonic resonant nanostructures. These arrangements function as nanoantennas, serving the dual purpose of enhancing light–matter interactions and decoupling the emitted photons. However, there is a contradiction between the requirements for these two tasks. A small resonator volume is necessary for maximizing interaction efficiency, while a large antenna mode volume is essential to achieve high emission directivity. In this work, we analyze a hybrid structure composed of a noble metal plasmonic resonant nanoparticle coupled to the atom-like emitter, which is designed to enhance the emission rate, alongside a corner reflector aimed at optimizing the angular distribution of the emitted photons. A comprehensive numerical study of silver and gold corner reflector nanoantennas, employing the finite difference time domain method, is presented. The results demonstrate that a well-designed corner reflector can significantly enhance photon emission directivity while also substantially boosting the emission rate. Full article

A disruptive Electric Propulsion system is proposed for next-generation Low-Earth-Orbit (LEO) small satellite constellations, utilizing an RF-powered Helicon Plasma Thruster (HPT). This system is built around a Magnetically Enhanced Inductively Coupled Plasma (MEICP) reactor, which enables acceleration of quasi-neutral plasma through a magnetic nozzle. The MEICP reactor features an innovative design with a multi-dipole magnetic confinement system, generated by neodymium iron boron (NdFeB) permanent magnets, combined with an azimuthally asymmetric half-wavelength right (HWRH) antenna and a variable-section ionization chamber. The plasma reactor is followed by a solenoid-free magnetic nozzle (MN), which facilitates the formation of an ambipolar potential drop, enabling the conversion of electron thermal energy into ion beam energy. This study explores the impact of an inhomogeneous magnetic field on the heating mechanism of the HPT and highlights its multi-mode operation within a pulsed power range of 200 to 500 W of RF. The discharge state, characterized by high-energy electron-excited ions and low-energy excited neutral particles in the plasma plume, was analyzed using optical emission spectroscopy (OES). The experimental testing campaign, conducted under pulsed power excitation, reveals that, as RF input power increases, the MEICP reactor transitions from inductive (H-mode) to wave coupling (W-mode) discharge modes. Spectrograms, electron temperature, and plasma density measurements were obtained for the Helicon Plasma Thruster within its operational envelope. Based on OES data, the ideal specific impulse was estimated to exceed 1000 s, highlighting the significant potential of this technology for future LEO/VLEO space missions. Full article

The very low frequency (VLF) communication system is characterized by a limited transmit bandwidth. Due to the low operating frequency, the dimensions of VLF antennas are significantly smaller than the corresponding wavelength. Therefore, VLF antennas are considered electrically small antennas (ESAs) with high Q values and narrow bandwidth. To achieve broadband VLF communication, synchronous tuning technology is commonly employed. In this study, we focus on analyzing the performance of the switching device in the synchronous tuning system using coupled inductors and IGBT as core components. By considering the equivalent circuit of the controlled source associated with coupled inductors, we propose an adaptive input impedance optimization algorithm based on the variable capacitor (hereinafter referred to as VC-ADIO) to address issues arising from coupling coefficient variations and internal parameters within IGBTs that affect primary loop input impedance. The radiated power of the VLF antenna is improved effectively. Full article

A Doppler velocity simulation method based on serrodyne modulation is proposed to achieve the frequency shift from hundred hertz to megahertz. One sub-phase modulation (PM) in a dual-parallel dual-drive Mach–Zehnder modulator loads a sawtooth signal to achieve a small frequency shift of the optical carrier. The other three sub-PMs implement carrier-suppressed double-band modulation of the RF signal. The RF signal is directly coupled from the receiving antenna to the modulator’s RF port without any electrical devices like a 90° hybrid, which ensures a broad operational bandwidth of the system. After filtering out one of the RF modulation sidebands by an optical filter, Doppler frequency shifting (DFS) is realized through frequency beating. The half-wave voltage of modulators rapidly decreases at low frequency shifts, leading to an increase in spurious signals. In order to improve the spurious suppression ratio (SSR) of DFS, a digital pre-distortion compensation based on the measured half-wave voltage is implemented in the frequency domain. Experimental results show that SSRs are larger than 35 dB when frequency shifts range from 0.1 kHz to 1 MHz. The RF operation bandwidth covers 2–40 GHz. The effectiveness of a Doppler velocity simulator is evaluated, and the simulation velocity error is less than 0.06 km/h. The proposed method has potential applications in both broadband electronic warfare and traffic metering applications. Full article

Wide-angle mechanical beam steering for on-the-move satellite communications is presented in this paper based on a closed-form pillbox antenna system. It includes three main parts: a fixed-feed part, which is a substrate-integrated waveguide (SIW) horn with an extended aperture attached to a parabolic reflector; a novel quasi-optical system, which is a single coupling slot alongside and without spacing from the parabolic reflector; and a radiating disc, which is a leaky-wave metallic pattern. To make the antenna compact, pillbox-based feeding is implemented underneath the metallic patterns. The antenna is designed based on a substrate-guided grounded concept using leaky-wave metallic patterns operating at $20 \mathrm{G}\mathrm{H}\mathrm{z}$. Beam scanning is achieved using mechanical rotation of the leaky-wave metallic patterns. The proposed antenna has an overall size of 340 × 335 × 2 mm³, a gain of $23.2 \mathrm{d}\mathrm{B}\mathrm{i}$, wide beam scanning range of $120°$, from $-60°$ to $+60°$ in the azimuthal plane, and a low side lobe level of $-17.8 \mathrm{d}\mathrm{B}$ at a maximum scan angle of $60°$. The proposed antenna terminal is suitable for next-generation ubiquitous connectivity for households and small businesses in remote areas, ships, unmanned aerial vehicles, and disaster management. Full article

The aim of this paper is to demonstrate progress in textronic UHF RFID transponder (RFIDtex tag) technology. The fundamental idea behind the RFIDtex tag design involves galvanic separation between circuits of the sewn antenna and the chip, which are electromagnetically coupled through a system of inductive loops. To advance the development of this concept, it is crucial to detect factors affecting the performance of the transponders. To achieve this goal, a mathematical model of the textronic UHF RFID transponder was developed. It involves relationships that describe the impedance of each element, the mutual inductance of the loops, and the chip voltage, and it enables the exploration of the influence of these variables on general parameters such as impedance matching and read range. Various analytical and numerical approaches were considered to obtain the value of the mutual inductance of the loops. The dimensions and geometry of the antenna, as well as the matching circuit in the microelectronic module, were taken into account. Based on the mathematical model, it was determined that mutual inductance strongly affects the chip voltage for frequencies higher than 800 MHz. The calculations from the mathematical model were compared with numerical simulations. Experimental studies were also conducted to investigate how the transponder performance is affected by either the distance between the centers of the loops or the conductivity of the threads used to embroider the antenna. The measurement results allowed us to conclude that even small imperfections in the manufacturing of the transponder, which slightly increase the vertical or horizontal distance between the centers of the loops, cause a dramatic decrease in the mutual inductance and coupling coefficient, significantly impacting the transponder’s performance. Full article

This paper presents a super-wideband multiple-input multiple-output (SWB MIMO) antenna with low profile, low mutual coupling, high gain, and compact size for microwave and millimeter-wave (mm-wave) fifth-generation (5G) applications. A single antenna is a simple elliptical-square shape with a small physical size of 20 × 20 × 0.787 mm³. The combination of both square and elliptical shapes results in an exceptionally broad impedance bandwidth spanning from 3.4 to 70 GHz. Antenna dimensions are optimized using the trust-region algorithm to enhance its impedance bandwidth and maintain the gain within a predefined limit across the entire band. For that purpose, regularized merit function is defined, which permits to control both the single antenna reflection response and gain. Subsequently, the SWB MIMO system is constructed with four radiators arranged orthogonally. This arrangement results in high isolation, better than 20 dB, over a frequency band from 3.4 to 70 GHz band. Further, the system achieves an average gain of approximately 7 dB below 45 GHz and a maximum gain equal to 12 dB for 70 GHz. The system exhibits excellent diversity performance throughout the entire bandwidth, as evidenced by the low envelope correlation coefficient (ECC) (<3 × 10⁻³), total active reflection coefficient (TARC) (≤−10 dB), and channel capacity loss (CCL) (<0.3 bit/s/Hz) metrics, as well as the high diversity gain (DG) of approximately 10 dB. Experimental validation of the developed SWB MIMO demonstrates a good matching between the measurements and simulations. Full article

This study introduces a monopole 4 × 4 Ultra-Wide-Band (UWB) Multiple-Input Multiple-Output (MIMO) antenna system with a novel structure and outstanding performance. The proposed design has triple-notched characteristics due to CSRR etching and a C-shaped curve. The notching occurs in 4.5 GHz, 5.5 GHz, and 8.8 GHz frequencies in the C-band, WLAN band, and satellite network, respectively. Complementary Split-Ring Resonators (CSRR) are etched at the feed line and ground plane, and a C-shaped curve is used to reduce interference between the ultra-wide band and narrowband. The mutual coupling of CSRR enables the MIMO architecture to achieve high isolation and polarisation diversity. With prototype dimensions of (60.4 × 60.4) mm², the proposed antenna design is small. The simulated and measured results show good agreement, indicating the effectiveness of the UWB-MIMO antenna for wireless communication and portable systems. Full article

The purpose of this article is to analyze the front door coupling effect that may occur in the projectile receiver due to the discharge pulse radiation in electromagnetic railguns, and to simulate the discharge pulse interference. This phenomenon will have an impact on the launch of the projectile, causing its fuse to be disturbed, ultimately affecting the weapon performance of the electromagnetic railgun. Discharge refers to when the armature carrying the projectile is fired out of the chamber, and the armature connected between the two rails detaches, causing a circuit break in the electrical circuit during the operation of the electromagnetic railgun. The current flowing through the armature is disturbed, causing an instantaneous high voltage to penetrate the air gap between the two rails, generating nanosecond pulse width discharge voltage pulse radiation, with a spectrum of up to tens of megahertz. In this paper, we establish a receiving antenna model on the projectile, which is essentially a horn antenna, receiving electromagnetic pulses from the discharge process, and coupling the pulse interference through its front door. During the analysis and calculation, we established an antenna receiver model located in the C-band with a frequency of 6 GHz for simulation, analyzed and calculated the actual interference loaded on the projectile after front door coupling, and verified the correctness of the simulation settings and results by comparing with the literature. Finally, we found that because the main energy spectrum of the pulse is at MHz level, when the front door of the C-band horn antenna is coupled, the standing wave ratio of the antenna is very large and the gain is very small, so the pulse interference is filtered, which can make the interference finally loaded on the projectile insufficient to affect the normal operation of the projectile. At the same time, it is recommended to add an RF filter to the receiving channel to further enhance anti-interference ability, so as to ultimately enable the electromagnetic railgun to function properly. Full article