Search Results (885)

This paper presents a wideband pattern-reconfigurable antenna designed for 360° horizontal sensing with angle-of-arrival (AoA) estimation capability. The antenna features a unique three-layer planar architecture, where a microstrip circular array is integrated between two metallic plates to enhance radiation stability and bandwidth. By employing a single-pole four-throw (SP4T) switching circuit, the array generates four steerable beams covering the entire azimuthal plane. Experimental results show that the prototype achieves a 10 dB return loss impedance bandwidth of 50% (4.0–6.0 GHz) and a peak gain of 8.3 dBi. Based on this antenna, a correlation-coefficient-based AoA estimation approach is implemented. The measured results demonstrate reliable estimation performance, with a mean angular error of less than 1.5° over the 360° horizontal plane across the operating frequency range. The proposed design provides a compact and low-complexity solution for practical wideband direction-finding applications in next-generation wireless systems. Full article

This paper presents a compact fractal-based super-wideband multiple-input multiple-output (MIMO) antenna for millimeter-wave (mmWave) 5G new radio (NR) and prospective 6G applications. The MIMO system comprises four Koch fractal monopole elements integrated with a modified shared ground plane. By adopting the second Koch iteration, the antenna achieves enhanced impedance bandwidth and stable radiation behavior compared with lower-order iterations. The elements are arranged in a polarization-diversity configuration within a 30 × 30 mm² footprint on a 0.8 mm-thick Rogers RO4835 substrate (ε_r = 3.5, δ = 0.0025). The proposed design provides an impedance bandwidth exceeding 14 GHz over 26.5–41 GHz, covering key bands at 28, 32, 38, and 40 GHz, while maintaining high inter-element isolation (around 30 dB over the operating range). The optimized ground modification enables a fully connected common ground and suppresses mutual coupling without additional decoupling structures. The antenna achieves 4–6 dBi realized gain with radiation efficiency exceeding 95%. MIMO performance metrics, including the envelope correlation coefficient (ECC), mean effective gain (MEG), and diversity gain (DG), confirm excellent diversity characteristics. The antenna is further evaluated under bending, demonstrating stable matching and isolation for conformal and wearable scenarios, and the concept is extendable to a non-planar 12-port configuration within the same footprint. Measured results agree well with simulations, validating the proposed design for wideband mmWave 5G/6G devices. Full article

This paper presents a compact modified monopole antenna tailored for 5G NR on-glass automotive applications operating in the n78 band. The design overcomes 3D radiation pattern limitations inherent in conventional monopole and inverted-F antennas (IFAs). Unlike traditional structures where auxiliary branches serve impedance matching or grounding, this design integrates open- and short-circuited stubs with a coplanar waveguide (CPW) feed to eliminate discrete components. By utilizing a resonant mechanism distinct from IFAs, it enables precise control over the current distribution and phase on the radiator to achieve passive 3D beam shaping without active switches or arrays. This suppresses the inherent elevation null, enhancing upper-hemisphere radiation. A prototype operating from 3.3 to 3.6 GHz was fabricated on a flexible printed circuit (FPC) and verified on a glass substrate. This study focuses strictly on radiation characteristics at the antenna element level; to ensure a focused investigation on dielectric-antenna interactions, large-scale vehicle body scattering and full-scale vehicle integration are excluded from this scope. The results, including S-parameters, gain, total efficiency, and 3D patterns, demonstrate superior elevation coverage and comparable impedance performance under on-glass boundary conditions. The proposed methodology offers a high-feasibility, low-complexity, and cost-effective solution for passive 3D radiation control in on-glass 5G wireless links. Full article

In this paper, a high-gain wideband filtering antenna with metasurface structures is presented for Sub-6 GHz 5G applications. The proposed antenna consists of a 3 × 3 metasurface array, a driven patch, a short-circuited stepped impedance resonator (SIR) feedline, and two parasitic patches. The metasurface is used to manipulate the modal behavior of the radiator and to introduce an additional resonant mode for bandwidth enhancement. Meanwhile, two radiation nulls are generated by different mechanisms to realize filtering performance. The low-frequency radiation null at 2.81 GHz is introduced by the short-circuited SIR feedline, whereas the high-frequency radiation null at 5.76 GHz is produced by radiation cancelation among the driven patch, parasitic patches, and metasurface. The measured results show a 10 dB impedance bandwidth of 35.5% from 3.62 to 5.18 GHz and an average realized gain of 8.61 dBi. In addition, the proposed antenna achieves lower- and upper-band selectivity of 42.57 dB/GHz and 33.43 dB/GHz, respectively. The proposed antenna also achieves a compact radiation aperture of 0.60 × 0.60 λ₀² and effective out-of-band radiation suppression, making it a promising candidate for integrated 5G RF front-ends. Full article

This paper presents a four-phase beam-steering antenna for 28 GHz wireless communication, targeting the demand for high-efficiency and low-complexity beam-steering solutions in millimeter-wave systems. The proposed design employs a Butler matrix network to achieve multi-directional beam switching while reducing implementation complexity. The antenna is realized using microstrip technology on a printed circuit board (PCB), and the overall architecture consists of a 1 × 4 microstrip antenna array and a 4 × 4 Butler matrix network. Each component is carefully designed and analyzed to ensure optimized performance and proper system balance. The proposed antenna exhibits excellent performance in terms of bandwidth and compact size, while also providing advantages that include low cost, ease of fabrication, and structural simplicity. The beam-steering capability is experimentally verified through far-field measurements. The measurement results indicate that the four beam directions are −38°, −13°, +19°, and +41°, with corresponding gains of 8.79, 9.66, 10.8, and 9.21 dBi, respectively. In addition, a good agreement between the measurement and simulation results is observed, which validates the effectiveness and feasibility of the proposed design. Full article

Ground-Penetrating Radar (GPR) serves as an essential non-destructive tool for subsurface exploration, and its antenna system largely determines the performance of the overall system. This paper presents a comprehensive review of advanced GPR antenna technologies, examining six major types: Vivaldi, bowtie, tapered, dipole, envelope, and spiral. This analysis shows that trade-offs among these antennas are unavoidable. High-frequency wideband antennas deliver high gain, but their penetration depth is limited to very shallow targets. Some wideband designs achieve wide bandwidth and reasonable gain with compact footprints, while others are suited for detecting embedded metallic objects. By comparison, low-frequency designs operating in the VHF and UHF bands enable very deep penetration, making them suitable for detecting deeply buried targets in lossy media and subsurface utilities. However, deep penetration often comes at the cost of lower gain or larger physical size. Ultimately, no universal antenna exists; the optimal choice depends on whether depth, resolution, or adaptability to attenuating environments is prioritized. Emerging metasurface-integrated and frequency-selective surface (FSS)-backed antennas represent a promising frontier, enabling better bandwidth, gain, and compactness. Ongoing challenges include miniaturization without compromising performance, reliable operation in heterogeneous and lossy soils, and the development of robust, manufacturable designs for field deployment. This review offers researchers and practitioners a structured reference, guiding the development of next-generation GPR systems that balance deeper penetration, higher resolution, and operational versatility. Full article

As essential radiating elements in RF and microwave microsystems, microstrip antennas require sufficient bandwidth to ensure stable operation, integration flexibility, and overall microsystem performance. From a microsystem optimization perspective, this paper proposes a bandwidth extension method for microstrip antennas that combines swarm intelligence and reinforcement learning. The proposed ICOA-TD3 framework is designed to enhance antenna bandwidth within target frequency bands and thus improve the performance robustness of compact RF microsystems. In the proposed method, an improved crayfish optimization algorithm (ICOA) is first used to explore the global design space and achieve global bandwidth enhancement, followed by the Twin Delayed Deep Deterministic Policy Gradient (TD3) algorithm for local refinement and further exploitation of the antenna structure’s bandwidth potential. In Experiment 1, the impedance bandwidth ($S_{11}\le -10\mathrm{dB}$) is increased by up to 200%. In Experiment 2, the impedance bandwidth ($S_{11}\le -10\mathrm{dB}$) and axial-ratio (AR) bandwidth ($\mathrm{AR}\le 3\mathrm{dB}$) are improved by up to 27% and 250%, respectively. The results indicate that the proposed method is a feasible solution for bandwidth-oriented optimization of microstrip antennas and is promising for the intelligent design of high-performance RF microsystems. Full article

This study explores the miniaturization of the Controlled Reception Pattern Antenna (CRPA) for Global Positioning System (GPS) receivers, addressing the challenge of mutual coupling, which adversely affects antenna performance. In this work, a miniaturized CRPA is designed and manufactured by using Rogers RO3006 substrate. To provide a performance benchmark, a four-element reference CRPA array was also designed with a 0.5 λ inter-element spacing, yielding an overall aperture size of 149.58 mm × 150.24 mm and a worst-case inter-element isolation larger than 14.4 dB. For the miniaturized CRPA, the target inter-element spacing was set to be 0.3 λ. To overcome isolation limitations, several coupling-mitigation techniques were developed and integrated into the miniaturized design. The final configuration consisted of a four-element CRPA, with each element rotated by 90° relative to its neighbor, inter-element slots incorporated into the shared ground-plane, and an individual ground plane segmentation to reduce surface–wave coupling. The proposed miniaturized CRPA achieved an overall footprint of 104.21 mm × 104.55 mm with the worst-case isolation exceeding 18.36 dB, surpassing the isolation performance of the reference array. This work demonstrates that it is possible to realize a compact CRPA with enhanced inter-element isolation by integrating tailored coupling suppression methods. Full article

The convergence of artificial intelligence, biotechnology, and the Internet of Bio-Nano Things (IoBNT) is enabling the creation of a new generation of intelligent in-body medical devices for continuous diagnosis and monitoring. In this context, a compact, wideband, circularly polarized conformal microstrip antenna is proposed for capsule endoscopy applications. The antenna is integrated along the inner wall of a 10 mm-diameter capsule and achieves an impedance bandwidth of 2.06–5.39 GHz (89.39%), maintaining stable matching under varying biological tissue conditions. A 3 dB axial ratio bandwidth (ARBW) of 2.31–3.14 GHz (30.45%) ensures reliable circular polarization and robust wireless communication in lossy and dynamic in-body environments. To extend beyond conventional electromagnetic analysis, a physics-informed neural network (PINN) framework is introduced to model the thermal response of biological tissues based on the governing bioheat equation. This AI-driven approach enables fast and generalizable prediction of temperature rise under varying operational conditions without repeated numerical simulations. At 2.45 GHz, the antenna exhibits a maximum gain of $-31.1$ dBi with a radiation efficiency of approximately $-34$ dB, consistent with in-body propagation constraints. Simulation and experimental results in realistic tissue phantoms, including muscle, small intestine, large intestine, and stomach, confirm stable wideband and polarization performance. Specific absorption rate (SAR) analysis demonstrates compliance with IEEE C95.1-2019 safety limits, while link budget evaluation validates reliable telemetry over a 1–3 m communication range. The integration of advanced antenna design with physics-informed machine learning provides a scalable framework for intelligent, safe, and adaptive IoBNT-enabled capsule endoscopy systems. Full article

Diamond nitrogen-vacancy (NV) centers are regarded as promising microwave sensors owing to their excellent magnetic sensitivity, stability, and environmental compatibility. However, traditional confocal test platforms based on diamond NV centers are bulky, which limits their practical applications. In this paper, a fiber-coupled compact NV microwave magnetometer is designed that employs the continuous heterodyne measurement method and a fast Fourier transform to measure multiple microwave fields. We integrated the laser excitation module, microwave antenna module, and fluorescence collection module into a single unit, reducing the volume of the magnetometer to 13 cubic centimeters. By adjusting the frequency and power of the measured microwave signals, the applicability of the device under different frequency and power conditions was verified. Experimental tests show that the microwave magnetometer can simultaneously detect multiple microwave fields with different frequencies and power levels, achieving a frequency resolution on the order of millihertz (mHz) and a microwave detection sensitivity of 0.385 nT/Hz^1/2. These results demonstrate the magnetometer’s multi-microwave-field measurement capability, making it highly promising for applications such as microwave anomaly localization and medical diagnosis. Full article

Radio frequency identification (RFID) technology has been widely adopted in a variety of practical applications. Usually, the size of a passive tag antenna largely determines the read performance of tag. However, excessively large tag antennas can hinder their practical application and a tag that is too small has poor performance. In this paper, a compact, flexible and corrosion-resistant folding dipole tag antenna is proposed, which has a geometrical dimension of 24 mm × 13 mm (0.074${\mathsf{\lambda }}_0\times 0.040{\mathsf{\lambda }}_0$). It is designed on only one surface of a flexible polyethylene terephthalate (PET) substrate, which can be folded. The paper proposes a single-sided laser-patterned GAF/PET flexible RFID tag that is mechanically folded to form a backside dipole arm without vias, targeting compact and corrosion-resistant UHF RFID operation. Changing the size of the folding arm can effectively adjust the resonant frequency and impedance of the tag antenna. A stepped radiation arm is used to extend the current path and lower the resonance frequency. The capacitance and inductance effects introduced by loading a T match for reducing the resonant frequency of the tag to the useful UHF RFID band. Finally, it can achieve a power transfer coefficient of 99.9% and exhibit high impedance matching between the tag antenna and the chip. The proposed tag antenna uses graphene-assembled film (GAF) as its conductor material. Thanks to the physicochemical properties of GAF, the proposed tag antenna maintains stable radiation performance even after prolonged exposure to acidic (5 wt%), alkaline (5 wt%), and salt (5 wt%) corrosion, as well as more than 1000 mechanical bending cycles. When the EIRP of the reader is 2.2 W, the maximum read range of the tag in the 800–1000 MHz is 1.38 m. Full article

A single-band-notched ultra-wideband (UWB) low-sidelobe planar array antenna for millimeter-wave (mmWave) applications is presented. The antenna element employs a planar dipole excited through an H-shaped coupling slot to achieve broadband impedance matching, while a centrally loaded parasitic patch acts as a half-wavelength resonator to generate a controllable notch band. Additional parasitic patches are introduced to recover the high-frequency matching without degrading the notch response. An $8\times 8$ array is then developed using a Taylor-weighted feed network implemented with three classes of 1-to-4 microstrip power dividers. Measured results show that the array operates from 19.0 to 45.0 GHz with $\mathrm{VSWR}<2$, while providing a rejection band from 35.0 to 38.5 GHz. The notch suppresses the realized gain by about 5 dB around 37.0 GHz, the peak gain reaches 20.5 dBi in the passband, and average sidelobe levels better than $-17$ dB are obtained. The proposed design provides a practical approach for combining ultra-wide bandwidth, in-band interference rejection, and low-sidelobe radiation in a compact mmWave planar array. Full article

This work presents the design and implementation of a flexible RFID tag based on a biocompatible and environmentally friendly conductive polymer, PEDOT:PSS, which is deposited onto a polyimide/fabric substrate using screen-printing techniques. The complete system consists of a dipole antenna based on PEDOT:PSS and a compact inductive metallic loop on a separate flexible printed circuit board (PCB) designed to match the capacitive impedance of a commercial RFID chip. The modular architecture, with the integrated circuit (IC) mounted on a reusable PCB substrate, shows efficient power transfer while allowing for easy disassembly, recycling, and consequently circularity of the PEDOT:PSS antenna and IC. By leveraging biocompatible materials and additive manufacturing processes, the proposed approach contributes to the advancement of sustainable and low-impact wireless technologies, addressing environmental concerns in next-generation electronics. Full article

This paper proposes a compact axial-ratio-enhanced wideband circularly polarized rectenna for ambient RF energy harvesting. The proposed rectenna is designed to operate across the mainstream Wi-Fi (2.45 GHz) and 5G (2.6 GHz and 3.5 GHz) communication bands, achieving efficient RF energy capture and effective direct current (DC) conversion. From a design perspective, the proposed approach is developed based on parasitic-element-enabled current redistribution for broadband circular polarization and nonlinear-aware multi-stage impedance matching for wideband rectification. The receiving antenna is based on a crossed-dipole configuration integrated with quarter-ring elements. By employing techniques such as slotting and incorporating additional parasitic patches, a fractional 3-dB axial ratio bandwidth (ARBW) of 52.7% (2.39–4.10 GHz) is achieved, with a peak radiation efficiency of 90% and an average efficiency of 76% within the operating band. To realize wideband impedance matching with the receiving antenna, the rectifying circuit adopts a single-shunt diode half-wave topology, combining L-type and T-type matching networks to significantly extend the operating bandwidth. Experimental results demonstrate that at input power levels of 7 dBm, 7 dBm, and 9 dBm, the rectifier achieves peak conversion efficiencies of 56.7%, 59.8%, and 56.3% at the three target frequencies (2.45 GHz, 2.6 GHz, and 3.5 GHz), respectively. Furthermore, the rectifier exhibits stable rectification performance across a wide input power dynamic range from −15 dBm to 7 dBm. Consequently, the proposed rectenna holds significant application value for passive IoT nodes, low-power sensors, and self-sustainable electronic devices. Full article

This paper introduces a compact MIMO antenna system designed for WLAN applications, offering dual polarization, strong isolation, and pattern diversity. The system includes two orthogonally positioned inverted-F antenna (IFA) elements operating in the 2.4 GHz WLAN band. To achieve polarization diversity, each element is designed and excited with a perpendicular feed. An L-shaped metallic parasitic element is placed close to the antennas to significantly reduce mutual coupling and enhance isolation. The antenna’s layout is straightforward and planar, making it easy to fabricate without requiring complex manufacturing steps. A prototype of the design was built and tested, and the experimental results show good agreement with simulated data. The fabricated antenna achieves a wide operating bandwidth from around 2.2 to 2.7 GHz and exhibits excellent port isolation, with S₂₁ better than −30 dB at 2.4 GHz. The proposed antenna with L-parasitic provides an efficiency of around −0.53 dB (89%) and a peak gain of 3.3 dBi at 2.4 GHz. Further, it offers an exceptionally low envelope correlation coefficient (ECC), approximately 0.0004, and diversity gain of nearly 10 dB, ensuring robust diversity and MIMO performance. These characteristics make the proposed design a promising option for use in low-profile modern WLAN MIMO systems. Full article