Abstract This paper proposes a balanced filter design method based on multi-mode ring resonators. By optimizing the resonator structure, independent control of center frequencies of the dual passbands is achieved. Additionally, parallel-coupled feeding is adopted, and the external quality factor is adjusted by tuning the spacing between the feed lines and resonators, enabling independent optimization of the bandwidth for both passbands. Experimental results show that the filter achieves a return loss of less than −17 dB within the dual passbands, an inter-passband isolation exceeding −40 dB. The minimum common-mode mode (CM) suppression of the differential mode (DM) passbands are 41.9 dB and 42.2 dB. The fabricated and tested filter demonstrates good agreement between simulation and measurement results.
In the paper, a dual-band microstrip bandpass filter (BPF) featuring high selectivity and quasi-independently reconfigurable frequencies is proposed. The proposed BPF is realized using two sets of asymmetric quarter-wavelength short stub-loaded resonators. The source-load coupling is achieved by adopting a parallel-coupled three-line structure, which can generate multiple transmission zeros (TZs) and enhance the selectivity of each passband greatly. By adjusting the electrical length ratio of the resonators, the center frequencies of the two passbands can be controlled quasi-independently. Ultimately, four varactor diodes of SMV1430 are employed to realize the dual-band reconfigurability. The tuning ranges of the two passbands of the proposed BPF are 430 MHz and 900 MHz, respectively, with insertion loss consistently below 5 dB across the entire tuning range. To validate the design methodology, a prototype of the filter was fabricated and tested, demonstrating good correlation between measured and simulated results.
In the THz spectrum, Graphene exhibits immense potential for the development of ultra-compact antennas due to its distinctive tunability feature. This paper presents a flexible wearable THz antenna using graphene nanomaterial for wireless body area network (WBAN) applications. The proposed antenna consists of a rectangular graphene patch placed over the polyamide substrate. The antenna design is optimized at 3 THz for on-body wearable applications. The body and bending effects of the proposed antenna are analyzed in this work. Specifically, the body effects, including the skin, fat, and muscle, with air gaps of different values, are investigated. The results show that the proposed graphene THz antenna holds great promise for WBAN applications.
This article presents the scheme of a tunable absorptive bandpass filter with an ultra-wide reflectionless range, which is composed of a tunable reflective BPF and a tunable reflective bandstop filter. A lowpass prototype for the absorptive bandpass filter with reflectionless characteristics at all frequencies is proposed, which is transformed into a bandpass circuit model using impedance converters while maintaining the reflectionless characteristics over the whole frequencies. In addition, parallel coupled lines are chosen to realize the absorptive filter, and varactor diodes are introduced to achieve the tunable characteristics. The proposed filter has been fabricated and the measurements show a tuning range of 38.7 % (from 1.02 GHz to 1.51 GHz) and a reflectionless range of over 20:1 (from 0.1 GHz to 2 GHz).
In the current years, the interest in the growth of advanced wireless transfer systems for biomedical applications is rising significantly. Microstrip Patch Antennas (MPAs), as critical components, enable seamless data transfer within internal medical devices and external monitoring systems. However, MPAs used in biomedical applications often face limitations such as limited multi-band operability and inefficient power transfer, which hinders their performance in complex biomedical environments. This research work presents the suggested MPA, meticulously engineered to resonate efficiently across 0. 403, 0.915, 1.4 and 2.45 GHz. The design process involves iterative optimization to achieve low return loss, stable radiation patterns, voltage standing wave ratio, and high gain. It also achieves a Avg specific absorption rate of 1.9590, 1.9970, 1.8236, and 1.6954 W/kg for all he four operational frequencies of the presented QBMPA in 10 g tissues. Complementing the antenna is the presented rectifier, achieving minimal power reflection and maximum energy conversion efficiency. The rectifier reaches up to approximately 60 % for 10 dBm power. Together, the multiband antenna and rectifier form a efficient and robust system for Wireless Power Transfer (WPT), enhancing the functionality and reliability of implantable medical devices.
A three-dimensional particle-in-cell (PIC) code, CST particle studio is used to examine the output performance of a 10 kW CW S-band magnetron under the effect of DC electric field priming using hollow annular sector cathode. It is found that hollow annular sector cathode enhances the efficiency of magnetron and reduce its startup time. A parametric study is carried out to optimize the cathode annular sector angle. It is found that efficiency is enhanced by 3.92 % and startup time is reduced by 54 % for optimized cathode annular sector angle of 6 degrees. The effect hollow annular sector cathode with conical end hat on magnetron performance is also examined and it is found that it enhances the efficiency by 6.5 %
A novel etched substrate-integrated half-coaxial line (ESIHCL) is proposed and utilized to compose a shielded low-pass filter with high performance. In comparison with substrate integrated coaxial lines (SICLs), the characteristic impedance of the proposed structure is significantly enhanced and can be modified flexibly, making it highly suitable for implementing the inductive components of low-pass filters. Finally, a fifth-order Chebyshev low-pass filter with a ripple factor of 0.1 dB and a cut-off frequency of 0.85 GHz was designed by combining the high-impedance features of the new proposed ESIHCL and the low-impedance characteristics of the conventional SICL. The experimental results indicate that the designed low-pass filter achieves a minimum insertion loss of -0.2 dB and exhibits a wide 20 dB stopband from 1.197 to 18 GHz, which is employed in a compact size of only 0.0097 lambda g2. Moreover, its roll-off rate (ROR) reaches 53.628 GHz, demonstrating higher advantages in terms of filtering passband loss, stopband suppression, and size optimization. These characteristics make the filter highly suitable for modern RF systems, and are of great significance in reducing the size of RF systems in microwave regime.
This paper addresses the power allocation problem in a network where joint information-theoretic secrecy and covert communication are required. In this network, a single transmitter (Alice) sends information to two legitimate users (Bob and Carol). There is also an untrusted user who attempts to detect the content of Bob's message and a warden (Willie) who wants to detect the existence of communication between Alice and the two users. Thus, Carol requires covert transmission, and Bob requires secure and covert communication. The network utilizes a friendly jammer to address these demands and overcome the low transmission rate of covert communication. To achieve covert communication, Alice sends both users' data simultaneously in selected time slots to hide it from Willie, while the jammer continuously transmits signals in all time slots. The objective is to maximize the average transmission rate over the allocated powers of Bob, Carol, and the jammer while meeting the two users' requirements. A novel iterative algorithm is proposed to obtain an effective solution. Simulation results indicate that the proposed method can enhance the network's average rate while satisfying the users' demands.
A practical method for comparing the intrinsic electromagnetic attenuations of bulky materials has been introduced. This approach employs normal incidence reflection (S_11) only measurements of metal-backed walls constituted by building materials and relies on accurate processing of echoes from metal plates through a time gating algorithm. The resulting attenuation parameter alpha_diff reflects the difference in attenuation constants of two distinct materials per unit length. The technique has been validated using point scattering simulation and applied to 1-3 GHz real experimental data collected from two primary building materials: bims (or pumice) concrete and clay brick. The frequency variation of this relative measure has been evaluated, given the importance of understanding how these materials affect rubble-penetrating radar and other relevant applications.
The airborne circular synthetic aperture radar (CSAR) can be used for the continuous and daylight independent surveillance. In case of small flying platforms, it is attractive to use a broadband frequency-modulated continuous wave (FMCW) radar and to transmit the sensor data to a ground station inside the measurement area for CSAR signal processing to save on-board resources. Thus, a joint FMCW radar and wireless communication system is needed. We propose and investigate frequency division multiplex (FDM) of broadband FMCW radar and single-carrier quadrature phase-shift keying (QPSK) communication using a single high power amplifier (HPA) for saving weight, size, power consumption and costs. Because of the HPA characteristics it is necessary to insert a frequency gap between the broadband linear chirp and the communication bandwidth. In case of an example scenario, the increase in overall bandwidth is only around 2.5 % of the radar bandwidth at 500 m flight altitude. It is shown that the transmit power of the communication part can be reduced to 13.4 dBm compared to the radar part with 30 dBm for maximal 500 m altitude. This enables power balancing for reducing intermodulation products of the HPA. Therefore, the reduction of the overall bandwidth by using a 70 % smaller frequency gap between the two frequency bands is possible. By using this power balancing the spectral efficiency is increased from 0.67 bps/Hz to 1.03 bps/Hz, but the power efficiency of the HPA is decreased by only 2.41 %. Therefore, it shows better performance for such applications than the linearity-hungry orthogonal FDM technique.
This research presents CALTESDRFLMO, an integrated platform designed to improve wireless image transmission through the combined use of LTE waveforms, Software-Defined Radio (SDR), fuzzy logic optimization, and Cassegrain antenna architecture. In the proposed system, images are encoded using LTE waveforms and transmitted as segmented MAC Service Data Units via SDR hardware. Fuzzy logic is employed to intelligently optimize critical transmission parameters-including bandwidth, spectral efficiency, and bit error rate-by fine-tuning associated membership functions. Experimental evaluation demonstrates significant improvements in image quality, signal integrity, and reliability across diverse bandwidth conditions. The fuzzy-optimized framework notably reduces bit error rates and enhances spectral efficiency, confirming the robustness of the Cassegrain-assisted SDR transmission model. Overall, the CALTESDRFLMO platform delivers a high-efficiency and reliable solution for long-distance wireless image communication.
Enabling performance improvements provided by reconfigurable intelligent surface (RIS)-assisted wireless communications requires precise channel estimation. However, none of the current techniques account for the impact of synchronization issues such as carrier frequency offset (CFO). To improve the accuracy of channel estimation in large Multiple-input, multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems, especially under rapid subcarrier variation, by developing a novel deep learning-based framework that surpasses traditional interpolation techniques in reliability, scalability, and performance under complex communication scenarios. The proposed ODS-DLRACG-Net SGA integrates multiple orthonormal discrete S-transform for signal reconstruction with a Deformable Long Range Attention Convolutional Graph Network, optimized by the Snow Geese Algorithm, to model nonlinear mappings between pilot symbols and channel responses effectively. Simulation results demonstrate that the proposed model significantly outperforms conventional techniques in large MIMO settings, achieving a lower bit error rate, root mean squared error, mean squared error, and normalized mean squared error (RMSE, MSE, and NMSE), thereby confirming its high accuracy and robustness in dynamic and high-dimensional wireless communication environments. ODS-DLRACG-Net SGA offers a robust and scalable solution for channel estimation in massive MIMO systems, effectively addressing challenges of fast-varying channels and nonlinear relationships, thus enabling more efficient and reliable data transmission in future communication networks.
This article presents a compact dual-band skin implantable antenna for biomedical applications in the ISM 2.4 GHz band and WMTS 1.4 GHz band. An effective permittivity calculation technique was used to ensure antenna operation at the desired bands. It exhibits a compact volume of 0.0984 λ 0 × 0.082 λ 0 × 0.00468 λ 0 . This study presents a complete system comprised of a Wireless Power Transmitter antenna (WPT X ), a rectifier, and an implantable antenna. The WPT antenna has been designed at 1.4 GHz frequency with dimensions of 6 cm × 6 cm × 0.32 cm. The WPT antenna has been used for wireless charging of a static implant and with the parasitic element (consisting of a triple ring) the coupling between WPT and the implantable antenna is improved by 11.57 dB. The rectifier has been optimized for 1.4 GHz and used a voltage tripler topology, with a high RF-to-direct current rectification efficiency of 58.6 %. The fabricated WPT and implantable antennas are tested and measured to validate their characteristics. For analysis of Specific Absorption Rate (SAR), the bare antenna was studied in the human scalp and skin phantoms. WPT SAR compliance has been studied and goes well with international guidelines for SAR.
In this communication, a single-layered (resistive ink-dielectric-metal based) wide-band frequency selective surface microwave absorber using a unique pattern of resistive ink is presented analytically and experimentally for the reduction of radar cross section (RCS) in stealth technology. As compared to multilayer designs, single layer designs are more easy to deploy in practical applications like stealth technology. Further in contrast to other options, resistive ink has numerous benefits, including consistent wideband absorption, uniform resistance distribution, low cost, and material flexibility. In this work four-fold symmetric topology based on resistive ink is imprinted using screen printing technology on a copper-backed FR-4 dielectric substrate to yield polarization insensitive response. Absorptivity over 90 % has achieved over the frequency range of 17.2–26.5 GHz, associated to a fractional bandwidth of 42.5 % for normal incidence of electromagnetic (EM) wave with two absorption peaks at 19.4 GHz and 22.9 GHz covering the K U and K bands. In the entire band, more than 20 dB monostatic RCS reduction is obtained with a maximum RCS reduction of 38 dB at 22.9 GHz. Current distribution on the upper and lower surface, along with the induced electric fields at absorption peaks, and equivalent circuits have presented to examine the absorption mechanism. The proposed design is evaluated for transverse electric (TE) and transverse magnetic (TM) waves under oblique incidence, and for varying polarization angles in TE and TM mode, demonstrating wide angular stability. A prototype has been fabricated, and the measured outcomes are compared and validated against the simulation results. The novelty of the proposed absorber lies in its distinctive single layer λ 1 /11 ( λ 1 corresponding to the lower absorbing frequency) thin topology made from resistive ink, which shows polarization insensitivity and wide angular stability. All the above-mentioned attributes along with 18 % fractional bandwidth of 20 dB RCS reduction make it commercially appropriate for RCS reduction in stealth applications.
A stepped C shaped patch with parasitic elements symmetrically placed along the width of the driven patch produces a moderate gain 8.24 dBi at center frequency 3.5 GHz and wide band from 3.29 to 3.71 GHz (12 %). It covers both n77 and n78 band of 5G New Radio (NR) frequencies ranging from 3.3–4.2 GHz and 3.3–3.8 GHz respectively. C-Band (3.4–4.2 GHz) used for 5G, satellite communications and wireless broadband and 3GPP LTE-42 band (3.4–3.6 GHz) used for Long Term Evolution (LTE) and 5G deployments. The proposed design has a planar structure with substrate height 3.2 mm and ground plane dimension 41 mm × 110 mm. Fabricated prototype is tested with measured S 11 of <−10 dB throughout the intended bandwidth and provides unidirectional radiation pattern used for small cell outdoor applications. The antenna has an excellent overall efficiency of 97.73 %. Therefore, the proposed antenna prototype is suitable for outdoor small cell with broad spectrum under 5G new Radio 1(nR1) band.
This paper presents a comprehensive review highlighting the progress made over the last few years, illuminating the state of the art in antenna designs based on characteristic modes theory and its application. The ultimate objective of this review is to provide an inclusive study of the recent advancements in characteristic mode analysis to design and optimize various antenna structures. The study will provide a broad coverage of characteristic modes theory, the underlying theoretical framework, and its significance in designing effective antenna structures. Additionally, the step-by-step methodology for antenna design using characteristic mode theory in commercial EM solvers has been extensively discussed. This article will be beneficial for beginners to explore the potential of characteristic modes and its applications enable them to embark on innovation working in this exciting field.
This study delves various nature inspired soft computing optimization and their applications for solving complex electromagnetics optimization problems. As the discipline advances, the integration of soft computing and electromagnetics is expected to drive innovation and broaden the scope of various engineering fields. In the past, there have been efforts to exploit various nature based optimization techniques like Genetic Algorithm (GA), Ant Colony Optimization (ACO), Particle Swarm Optimization (PSO), Differential Evolution (DE), Evolutionary Strategy, Simulated Annealing (SA), Memetic Algorithm (MA), Bacteria Foraging Optimization (BFO), Comprehensive Learning Particle Swarm Optimization (CLPSO), Wind Driven Optimization (WDO) Technique and many more, for solving multi-modal and multi-dimension in area of electromagnetcis, communications, system identifications, power flow optimization, pattern recognition, biomedical, health-care and marketing management etc. Incorporating soft computing techniques – such as Neural Networks (NN), Wind Driven Optimization (WDO), and Genetic Algorithms (GA) etc. – into electromagnetics has demonstrated significant potential in overcoming complex challenges where traditional methods fall short. These methods enhance resilience against the inherent uncertainties and nonlinear characteristics of electromagnetic systems, leading to notable progress in design optimization, antenna pattern synthesis, and mitigating electromagnetic interference.
In this article, triple band polarization insensitive multiband metamaterial absorber is proposed for terahertz (THz) applications. The proposed unit cell size is of 140 × 140 µm 2 , consisting of a metallic radiator at the top layer with conducting ground plane of copper and polyamide substrate material with dielectric constant ε r = 4.3 and loss tangent tan δ = 0.004. Four concentric rings acting as resonators are designed to develop a triple band absorber. The proposed design is providing absorption at 0.615 THz, 0.951 THz and at 1.007 THz frequency with absorption of 97.5 %, 98.94 % and 99 % respectively. Due to symmetry in design, it is polarization insensitive from angles 0–60°. The results confirm that the proposed absorber design offers a wide range of THz applications in sensing, imaging and filtering.
In this paper, an improving technique is proposed and analysed to augment the performance of next generation radio over fiber (RoF) network. This is based on linearization microwave photonic link by employing two parallel dual electrode Mach-Zehnder modulator (DE-MZMs). Subsequently, the optical single sideband (OSSB) is generated by properly selecting the phase of input two tone RF signals & dc biases of DE-MZMs. The parallel arrangement of both DE-MZMs significantly reduces the third order intermodulation (IM3) and other harmonics in the proposed RoF network. The outcomes demonstrate an improvement of 56.54 dB in the signal to noise distortion ratio (SNDR) in distortion dominant situation for the proposed RoF network in comparison to the conventional network (90° phase shift based RoF network). These analytical results are also validated by simulation using OptSIM software and shows a close agreement. The proposed technique has the features of simple design of high linearized microwave photonic link and play a significant role to develop a backbone structure of future wireless networks.
The rapid advancements in wearable and implantable biomedical technologies have led to an increased demand for high-performance, miniaturized antennas capable of facilitating real-time health monitoring and seamless wireless data transmission. Conventional implantable antennas face challenges like mutual coupling, signal degradation, high SAR, and limited radiation efficiency, affecting medical communication in applications like ECG monitoring and neurostimulation. This study introduces a novel 2-element MIMO implantable antenna optimized using a Multi-Relational Hamiltonian Quantum Nutcracker Generative Graph Adversarial Attention Network (MR-HQNG-GAANet). The optimization framework integrates multi-relational graph learning with quantum-assisted adversarial tuning, enhancing radiation performance, impedance matching, and energy efficiency. By leveraging quantum-assisted adversarial tuning and multi-relational graph learning, the proposed design significantly reduces SAR levels while enhancing radiation efficiency, ensuring safe operation and robust wireless performance in implantable biomedical environments. Performance evaluation demonstrates superior characteristics, including a reflection coefficient of radiation efficiency of 86.4 % at 2.4 GHz and 81.2 % at 5.8 GHz, mutual coupling below −18 dB, −28.9 dB at 5.8 GHz, −32.6 dB at 2.4 GHz, and a max gain of −14.7dBi. Safety standards set by the FDA and IEEE (≤ 1.6 W/kg in 1g tissue) are met by SAR compliance, ensuring safe usage. The proposed optimization framework enhances impedance bandwidth, link reliability, and energy efficiency in wearable and implantable biomedical sensors, incorporating quantum-assisted graph learning for reliable data transmission.
