Search Results (128)

This research paper investigates the impact of inserting a ground slot on the frequency performance of a monopole-type microstrip patch antenna. To examine this, a reference antenna, which is a simple rectangular monopole with the dimensions 2.4 × 2.04 mm², was mounted on a 12 × 12 mm² Rogers RT 5880 substrate with a thickness of 0.254 mm and a dielectric constant of εᵣ = 2.2. It was also fed by a 50 Ω microstrip line. This work compares the effects of four different geometries of rectangular ground slots: rectangular, triangular, half-ring, and half-circle, on the performance of the microstrip patch antenna. The no-slot baseline antenna showed a resonance of 12.55 GHz and a reflection coefficient of −15.9 dB. Adding a ground slot allowed the advent of single or dual-resonant frequencies, which significantly enhanced the appropriateness of the antenna in 5G usage. Notably, the rectangular slot with b₁ = 3 mm achieved a resonance of 22.5 GHz, with a reflection coefficient of −33.7 dB, while b₁ = 1 mm enabled dual-band operation at 11.77 GHz and 38.3 GHz. Triangular slots provided strong single-frequency operation between 26 GHz and 31 GHz, and the half-circle slot with r₃ = 1 mm resonated at 12 GHz with a reflection coefficient of −39.5 dB. Although the half-ring slot had a comparatively lower reflection coefficient, it still showed dual-band potential at 11.1 GHz and 34.14 GHz. The simulation results were validated using HFSS, demonstrating good alignment. The gain of the selected antennas was also investigated, where the highest gain of 4.2 dBi was achieved by the half-ring slot design, and the lowest gain of 3.09 dBi was obtained with the half-circle slot. These findings confirm that ground-slot integration is an effective technique for frequency tuning and performance enhancement in 5G antenna design. Full article

The spread of unmanned aerial vehicles (UAVs) and unmanned free balloons (UFBs) has made ground-based air surveillance more difficult, especially for low, slow, and small (LSS) targets. Such targets often combine low radar cross-section (RCS), low altitude, small radial velocity, and strong coupling to ground clutter. This study provides a focused assessment of the detection constraints expected for a RAT-31DL-type long-range L-band surveillance radar against small UAVs and radiosonde-type light UFB payloads. The work combines simplified RCS estimates, literature-based UAV RCS data, finite element method (FEM) simulation, radar-horizon geometry, elevation-beam intersection analysis, and low-Doppler considerations. Idealized broadside reference RCS values are calculated at 1.5 GHz. Published 26–40 GHz UAV RCS data are used as comparison references and are back-scaled to the L-band to illustrate frequency-scaling uncertainty. A simplified FEM model of a trademark Meteomodem M20 radiosonde is simulated at 1.5 GHz and at 26 GHz for comparison, to examine aspect- and polarization-dependent scattering. The simulated radiosonde cross-polarized RCS values vary from approximately −36.49 to −23.45 dBsm at 1.5 GHz. For a 30 m radar installation and 60–140 m target altitudes, the smooth-Earth horizon-limited visibility range is approximately 55–71 km. Low-altitude coverage can be further limited by positive-elevation beam geometry. Taken together, the results indicate that LSS detectability is strongly scenario-dependent and is governed by RCS variability, geometric visibility, clutter, Doppler behavior, and radar-specific processing choices. Full article

Private 5G mobile networks are emerging as a platform for wireless connectivity in professional applications across smart industrial sectors such as automated warehousing, logistics, autonomous vehicle deployments in campus environments, mining, and material processing, among others. It is expected that most Machine-to-Machine (M2M) and Industrial Internet of Things (IIoT) communication links will increasingly rely on wireless solutions, as the flexibility they offer provides clear advantages over hard-wired network installations. To gain insight into workers’ exposure to radiofrequency electromagnetic fields (RF EMF) emitted by 5G private mobile networks, an analysis was conducted based on measured and calculated RF EMF levels from various 5G private networks in real-world scenarios across different smart industrial sectors and R&D platforms in three countries. Several exposure scenarios were evaluated, including production facilities, logistics operations, office environments, and research sites. The installations included different configurations: private standalone and non-standalone 5G networks operating at 3.5 GHz and 26 GHz, as well as public networks with private slicing. The results clearly demonstrated that exposure levels in all investigated scenarios were well below existing exposure limits. In a typical indoor industrial environment where pico 5G base stations are deployed, the measured exposure was found to be no greater than 0.006% of the Directive 2013/35/EU action value and 0.03% of the ICNIRP guideline limits for the general public. Full article

A reconfigurable broadband signal channelized reception technique based on parallel Mach–Zehnder modulators (MZMs) is proposed. In the upper branch, the unknown broadband signal is modulated onto the ±1st-order sidebands of a frequency-shifted optical carrier. In the lower branch, N parallel MZMs are employed, with each MZM generating two local oscillator (LO) comb lines, which beat with the broadband signal from the upper branch to produce 4N sub-channels. By adjusting the frequency shift of the acousto-optic frequency shifter (AOFS) and the frequency of the LO signals, the system achieves tunability over an operating frequency band of 8 to 40 GHz, enabling simultaneous tuning of the sub-channel bandwidth, the number of sub-channels, and their center frequencies. Simulation experiments show that this technique can down-convert a wideband signal with a frequency band of 12–16 GHz to eight intermediate frequency (IF) signals with eight center frequencies of 0.5 GHz and a bandwidth of 0.5 GHz and down-convert a wideband signal with a frequency band of 32–40 GHz to eight IF signals with eight center frequencies of 1 GHz and a bandwidth of 1 GHz, and the image rejection ratio (IRR) is greater than 26 dB, the passband power fluctuation is less than 0.5 dB, and the spurious-free dynamic range (SFDR) is 95.17 dB·Hz^2/3. Full article

The microwave permeability of composites containing microsized gadolinium powder in paraffin wax was studied as a function of frequency, temperature and gadolinium fraction for a series of composites with a powder volume fraction of 5% to 50%. The constitutive parameters of the composites were measured by the Nicolson–Ross–Weir technique in a standard 7 × 3 mm coaxial line in the frequency range of 0.1 to 10 GHz and the temperature range of 5 to 26 °C. In the indicated ranges, the permittivity was independent of frequency and temperature, and the real part of the permittivity only depended on the gadolinium powder volume fraction. It was found that the peak of the magnetic losses shifts towards lower frequencies with an increase in temperature. The Curie temperature of the composites found from the temperature dependence of the static permeability was close to 15 °C, being practically independent of the gadolinium volume fraction. To retrieve the intrinsic permeability of the filler particles, the Odelevsky mixing rule was used. The measured dependence of the static permittivity on the gadolinium volume fraction was in good agreement with the fitting by the Odelevsky mixing rule. Using the values of the percolation threshold and the depolarization factor obtained as a result of the fitting of the static permittivity, the frequency dependence of the intrinsic permeability of the filler particles was retrieved. The temperature effect on the intrinsic permeability was also analyzed. The obtained results may be useful for designing microwave devices, including temperature-tunable microwave screens and sensors. Full article

This paper presents the design and experimental validation of a compact low-pass filter based on a quasi-eight-shaped defected ground structure (DGS). The study begins with a single DGS resonator that perturbs the ground-plane current distribution, introducing additional effective inductance and capacitance. An equivalent circuit model is developed to provide physical insight into the resonant mechanism and to establish the relationship between the DGS geometry and the electromagnetic response. By incorporating microstrip stubs on the top layer, the resonant structure is transformed into a low-pass filtering configuration with improved passband characteristics. Subsequently, a higher-order topology composed of two identical quasi-eight DGS units and three microstrip stubs is implemented to significantly enhance the rejection performance and extend the stopband bandwidth. The fabricated prototype exhibits a measured cutoff frequency of approximately 2.1 GHz, with an insertion loss lower than 1 dB in the passband. A wide stopband extending from 2.8 GHz to 8 GHz is achieved, with attenuation exceeding 26 dB. The close agreement between the equivalent circuit model, full-wave electromagnetic simulations, and measured results confirms the effectiveness and physical consistency of the proposed design. Owing to its compact planar implementation and strong harmonic suppression capability, the proposed filter is suitable for microwave front-end and antenna applications. Full article

In this paper, inspired by the structural characteristics of the human eyeball, a bionically designed circular resonant structure is proposed, and a flexible chipless radio frequency identification (RFID) tag based on this concept is developed. By selectively adding or removing branch structures, the proposed tag achieves controllable resonant frequency shifts and distinguishable geometric pattern variations. Fabricated on a polyimide substrate with a compact size of 20 × 26 × 0.2 mm³, the tag achieves a coding capacity exceeding 45 bits while operating within an effective frequency bandwidth in 4–12 GHz, realizing a synergistic improvement in coding capacity and structural compactness under limited spectrum constraints. Simulation analyses are performed to investigate the encoding stability of the tag under various bending and rotational conditions relevant to flexible applications. Experimental results obtained under the unbent condition are consistent with the simulations, demonstrating the feasibility of the proposed chipless RFID tag. Full article

Non-contact monitoring of human vital signs using microwave radar has attracted increasing attention due to its capability to operate unobtrusively and through clothing or light obstacles. In vector network analyzer (VNA)-based radar systems, vital signs can be extracted from phase variations in the forward transmission coefficient $S_{21}$, whose sensitivity strongly depends on the electromagnetic performance of the antenna system. This work presents the design, optimization, fabrication, and experimental validation of a high-gain 12 GHz 4 × 4 microstrip patch antenna array specifically developed for phase-based vital signs monitoring. The antenna array was progressively optimized through coaxial feeding, slot-based impedance control, stepped transmission line matching, and mitered bends, achieving a simulated gain of 17.8 dBi, a measured gain of 17.06 dBi, a reflection coefficient of −26 dB at 12 GHz, and a total efficiency close to 74%. The antenna performance was experimentally validated in an anechoic chamber and subsequently integrated into a continuous-wave VNA-based radar system. Comparative measurements were conducted against a commercial biconical antenna, a single patch radiator, and an MIMO antenna under identical conditions. Results demonstrate that while respiration can be detected with moderate-gain antennas, reliable heartbeat detection requires high-gain, narrow-beam antennas to enhance phase sensitivity and suppress environmental clutter. The proposed array significantly improves pulse detectability in the (1–1.5) Hz band without relying on advanced signal processing. These findings highlight the critical role of antenna design in $S_{21}$-based biomedical radar systems and provide practical design guidelines for high-sensitivity non-contact vital signs monitoring. Full article

E/W-band millimeter-wave signals are highly promising for long-distance offshore wireless communications. However, the high humidity over the sea surface, together with the continuous fluctuation of sea waves, gives rise to severe near-sea-surface channel impairments, such as strong atmospheric absorption and sea-surface-induced multipath, which significantly hampers long-range E-band transmission. This work proposes a photonic-assisted E-band millimeter-wave 1 × 2 MIMO communication system and conducts a 26 km near-sea-surface transmission experiment in the coastal area of Lianyungang, Jiangsu Province. A 73.5 GHz 5-Gbaud QPSK signal is transmitted, and spatial diversity reception followed by maximal ratio combining (MRC) is applied. Experimental results show that diversity reception improves system performance by about 4 dB, demonstrating that the proposed photonic-assisted E-band spatial diversity system and signal processing method can significantly extend the transmission distance. Full article

In this paper, the dependence of the microstructure and properties on Spark Plasma Sintering modes of an AlN-35 β-SiC (wt.%) composite is investigated. It was found that the use of a heating rate of 100 °C/min during the sintering process of the AlN-35 β-SiC (wt.%) composite leads to the formation of a solid solution (AlN)_x–(SiC)_x−1 at 1900 °C during 5 min, and under a pressure of 50 MPa. It was observed that, at a heating rate of 50 °C/min and a pressure of 25 MPa, yttrium oxide used as a sintering additive impedes the diffusion of SiC into AlN. This impedes the formation of a solid solution (AlN)_x–(SiC)_x−1 and helps preserve SiC grains, which act as the main absorbing phase in the obtained composites. It is shown that the use of sintering additives and SPS technology allows obtaining samples with a density of 3.26 g/cm³, which coincides with the theoretical value of the composite. The dielectric characteristics and absorbing properties of sintered materials are determined in the frequency bands from 5.6 to 26 GHz. It has been discovered that the reflection, transmission, and absorption coefficients can be regulated depending on the thickness of the sample. In addition, it is shown that composites containing solid solutions and silicon carbide grains in their structures have the best absorbing properties. On the other hand, the material containing only solid solutions is a promising material that can be used as microwave filters. Full article

To address the limited overlapping bandwidth across polarization modes in conventional multi-polarized antennas, this paper proposes a wideband multi-polarized microstrip antenna with high polarization isolation. Based on the theory of orthogonal dual-circular polarization synthesis, the proposed antenna achieves left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) under a single-port excitation mode, and can generate arbitrary linear polarization (LP) by simply adjusting the phase when dual-fed. For verification, a prototype operating at the C-band is designed, fabricated, and measured. The measured results agree well with the simulations. For linear polarization, the measured 10 dB bandwidth ranges from 4 GHz to 8 GHz (relative bandwidth of 66.7%), with polarization isolation exceeding 26 dB. For circular polarization, the measured bandwidth (for 10 dB return loss and 3 dB axial ratio) spans 4.1–8 GHz (relative bandwidth of 64.5%), with polarization isolation greater than 15 dB. The linear polarization gain is slightly higher than the circular polarization gain, with a maximum gain of 4.3 dB. The proposed antenna simultaneously features multi-polarization, a wide bandwidth, a low profile (0.03 λ₀), and high polarization isolation, which can meet the urgent demand for multi-polarized antennas in modern multi-functional integrated wireless systems, such as communication systems, radar, and unmanned aerial vehicles (UAVs). Full article

A compact fork-shaped four-element multiple-input multiple-output (MIMO) antenna system with wide bandwidth for 5G millimeter-wave (mmWave) applications is presented. The antenna elements are arranged orthogonally to achieve a compact footprint of $20\times 26{\mathrm{mm}}^2$. To enhance the gain, a frequency selective surface (FSS) is placed above the MIMO system, providing an average gain improvement of 1.5 dB across the entire operating band and achieving a peak gain of 7.5 dB at 41 GHz. The proposed design operates in the Ka-band (22–46 GHz), making it well suited for 5G communications. The antenna exhibits an isolation greater than 20 dB and radiation efficiency exceeding 80% across the band. Moreover, key MIMO performance metrics, including diversity gain (DG ≈ 10) and envelope correlation coefficient (ECC < 0.05), meet the required standards. A prototype of the proposed system was fabricated and measured, with the experimental results showing good agreement with simulations. Full article

This paper presents an intelligent design framework for a high-performance 26 GHz MIMO antenna array tailored to 5G applications, built upon a compact single-element patch. The 11.5 mm × 11.5 mm × 1.6 mm microstrip patch on FR4 exhibits near-unity electrical length, an ultra-deep return loss (S11 < −40 dB at 26 GHz), and a wide operational bandwidth from 24.4 to 31.2 GHz (6.8 GHz, ~26.2%). A two-element array, spaced at λ/2, is first augmented with a inspired metamaterial (MTM) unit cell whose dimensions are optimized via a Multi-Layer Perceptron (MLP) model to maximize gain (+2 dB) while preserving S11. In the second phase, a closed-square parasitic ring is introduced between the elements; its side length, thickness, and position are predicted by a Random Forest (RF) model with Bayesian optimization to minimize mutual coupling (S12) from −25 dB to −58 dB at 26 GHz without significantly degrading S11 (remains below −25 dB). Full-wave simulations and anechoic chamber measurements confirm the ML predictions. The close agreement among predicted, simulated, and measured S-parameters validates the efficacy of the proposed AI-assisted optimization methodology, offering a rapid and reliable route to next-generation millimeter-wave MIMO antenna systems. Full article

This paper presents an advanced W-band bidirectional Power Amplifier–Low Noise Amplifier (PALNA) implemented using 130 nm SiGe BiCMOS technology. The proposed RF front-end eliminates the need for conventional transmit/receive (T/R) switches by employing a bidirectional architecture with a passive matching network. This approach minimizes area requirements and reduces signal losses. Post-layout simulation results demonstrate that the designed PALNA achieves a peak small-signal gain of 30 dB in Tx mode and 26 dB in Rx mode, with reverse isolation better than 40 dB. The 3 dB bandwidth spans from 94 to 106 GHz. In LNA mode, the design achieves a minimum noise figure of 6 dB at 100 GHz, remaining below 6.5 dB across the entire 3 dB bandwidth. In PA mode, the simulated saturated output power is 10.5 dBm, with a maximum power-added efficiency of 12% at 100 GHz. The chip size is 0.7 mm² including pads. It consumes 78 and 22 mW in the Tx and Rx modes, respectively. Full article

Novel K band wearable sensors and antennas for Telemonitoring, Telehealth and Telemedicine Systems, Internet of Things (IoT) systems, and communication sensors are discussed in this paper. Only in a limited number of papers are K band sensors presented. One of the major goals in the evaluation of Telehealth and Telemedicine and wireless communication devices is the development of efficient compact low-cost antennas and sensors. The development of wideband efficient antennas is crucial to the evaluation of wideband and multiband efficient Telemonitoring, Telehealth and Telemedicine wearable devices. The advantage of the printed wearable antenna is that the feed and matching network can be etched on the same substrate as the printed radiating antenna. K band slot antennas and arrays are presented in this paper the sensors are compact, lightweight, efficient, and wideband. The antennas’ design parameters, and comparison between computation and measured electrical performance of the antennas, are presented in this paper. Fractal efficient antennas and sensors were evaluated to maximize the electrical characteristics of the communication and medical devices. This paper presents wideband printed antennas in frequencies from 16 GH to 26 GHz for Telemonitoring, Telehealth and Telemedicine Systems. The bandwidth of the K band fractal slot antennas and arrays ranges from 10% to 40%. The electrical characteristics of the new compact antennas in the vicinity of the patient body were measured and simulated by using electromagnetic simulation techniques. The gain of the new K band fractal antennas and slot arrays presented in this paper ranges from 3 dBi to 7.5 dBi with 90% efficiency. Full article