Search Results (290)

In this article, a new approach to the applicability of the self-complementarity concept in a classical two-port microstrip patch antenna element is presented. This was accomplished through an illustrative design and an electromagnetic analysis of a broadband two-port rectangular printed radiating element in transmission configuration. A calculated ultra-wide matching bandwidth up to approximately 11 GHz was achieved (BW_{sim-RL≥10 dB} ≈ 11 GHz, f_o = 5.5 GHz, i.e., BW_{sim-relative-matching} ≈ 200%). One of the advantages of this topology is that only two degrees of freedom are needed to acquire a very wide impe-dance bandwidth: the length and the width of the slot. Full-wave analysis shows that sui-table combinations of the patch and slot dimensions allow to obtain the broadband mat-ching behavior. It has broadside radiation toward both hemispheres, which is conserved and considerably stable over a wide frequency range. Its linear polarization, radiation patterns, gain values, and radiation efficiency are adequate from 1 to 8 GHz (BW_{sim-radiation} ≈ 7 GHz, f_{o [sim-rad]} = 4.5 GHz, i.e., 63.6% of its BW_sim-matching, and 156% of its f_{o [sim-rad]}). Moreover, the gain and radiation efficiency exhibit very good flatness across wide frequency ranges. Measurements of S-parameters and radiation patterns validate the calculated results. The proposed antenna element is simple, compact, and light-weight. It has a very wide ope-ration bandwidth (7 GHz), its design is easy and flexible, and it is simple to manufacture. It could be used as a radiating element in different linear polarized antenna arrays. Full article

One of the strongest electromagnetic engineering approaches for enhancing antenna performance is the use of photonic crystal (PhC) substrates. This technique can be efficiently applied to antenna design and offers notable advantages, such as gain improvement, increased bandwidth, and frequency-dependent beam scanning. In this paper, a bow-tie dipole antenna has been developed for terahertz operation over the 0.39–1.3 THz band, presenting a novel structure capable of producing strong ultra-wideband (UWB) field enhancement within its feed gap. The feed gap between the two metallic arms has a slot width of 1.24 λ0 (λ0 is the wavelength in free space at a center range of 0.8 THz), which facilitates the generation of an enhanced electric field. The PhC substrate enables surface-wave control through dispersion engineering, thereby enhancing the radiation efficiency of the antenna. The proposed antenna exhibits a radiation efficiency of approximately 73–93% over the entire UWB frequency band. Furthermore, the PhC substrate antenna achieves a maximum gain of 21 dB, exceeding that of a homogeneous-substrate THz bow-tie antenna by at least 3.3 dB. The results indicate that the antenna achieves |S₁₁| < −10 dB impedance matching over the bandwidth of 105.9%, ranging from 0.4 to 1.3 THz. The proposed bow-tie dipole antenna integrated with a PhC substrate demonstrates a wide beam-scanning capability from −54° to +74° across the 0.39–1.16 THz band, while maintaining a compact footprint of 14.9 λ₀ × 22.4 λ₀. This combination of wide scanning, broad bandwidth, and ultra-low profile represents a notable advancement in the development of compact THz radiating structures. Full article

In this work, we report a dual-mode ferroelectrically programmable on-chip antenna. The antenna is built on a silicon wafer using complementary metal-oxide semiconductor (CMOS) processes and exhibits two programmable resonant modes: one in the super high frequency (SHF) range and one in the extremely high frequency (EHF) range. The SHF mode resonates at 8.5 GHz and exhibits ultrawideband (UWB) behavior, while the EHF mode resonates at 36.6 GHz. Both resonance frequencies can be tuned in a non-volatile fashion by controlling the ferroelectric polarization state of a Hafnium Zirconium Oxide (HZO) varactor monolithically integrated into the feed line. This programmability arises from the ferroelectric switching of the embedded HZO film, which results in a non-volatile variation of its permittivity upon application of a voltage pulse. Ferroelectric switching occurs at approximately ±3 V and induces maximum resonance frequency shifts of 381 MHz for the SHF mode and 3 GHz for the EHF mode, corresponding to fractional frequency changes of 4.5% and 8.3%, respectively. Unlike previously reported ferroelectrically tunable antennas, our reported antenna combines full integration, CMOS compatibility, higher operating frequency, compact footprint, and non-volatile programmability. Full article

In this study, we present and analyze a fully optically transparent four-port ultra-wideband (UWB) antenna intended for MIMO applications. The antenna’s design is thoroughly described and extensively analyzed, focusing on current distributions across its structure, with all behavioral parameters explained. The proposed antenna design has been validated with both simulations and measurements. The antenna demonstrates excellent performance in terms of port matching, isolation, and efficiency, achieving an efficiency of 40%, which is impressive compared to optically transparent antennas in the literature. The radiation characteristics exhibit peak gains up to 4 dB with stable, symmetric, and linear polarized patterns maintained across the entire UWB range. Regarding diversity performance, the antenna displays outstanding behavior with an envelope correlation coefficient of less than 0.0016 and a diversity gain around 10 dB across the entire operating band. The antenna’s exceptional performance along with its optical transparency makes it suitable for various applications, such as medical non-invasive devices that can be easily integrated into glasses without obstructing vision. It can also be combined with solar cells for energy harvesting and communication purposes. Additionally, its structure is suitable for vehicular settings and can be seamlessly integrated into vehicle mirrors or windows. Full article

The present work addresses the critical challenge of designing a lightweight antenna suitable for remote sensing applications specifically aimed at the identification of buried objects from Unmanned Aerial Vehicles (UAVs). The stability of the phase center and the radiation pattern are critical factors for enabling synthetic aperture radar (SAR) processing on moving platforms. The presented antenna structure is characterized by a simple, lightweight geometry, and allows for achieving a fractional bandwidth of nearly 100% with an excellent stability of the radiation pattern, that exhibits minimal variation within the operating band of the antenna. Specifically, the gain is in the range 4.4–6.3 dBi and the group delay spread is about 200 ps in the frequency range 1–2 GHz. We illustrate numerical simulations and measurements of an antenna prototype that validate the proposed approach, demonstrating the suitability of the design for the intended operational scenario. Full article

This paper proposes a complete cascade pipeline for accurate position and orientation estimation using a single dual-antenna UWB module. First, an extended Kalman filter (EKF) fuses distance measurements from multiple anchors to estimate the agent’s position. The estimated position is then used to derive orientation. To overcome the critical challenge of front–back ambiguity in orientation estimation, we introduce a novel method that integrates a multi-hypothesis testing (MHT) framework with a circular likelihood metric (CLM). This method enumerates all feasible angle of arrival (AoA) hypotheses via MHT and assesses their consistency using the CLM, thereby selecting the most probable hypothesis to resolve ambiguity. Comparative simulations demonstrate that this “position-first, orientation-later” cascade enhances robustness over joint optimization by preventing the propagation of AoA noise to the position estimates. Extensive evaluations, including high-precision rotary table experiment and real-world field trials, validate the system’s efficacy in providing precise location and heading information. This work delivers a complete, low-cost, and robust solution for autonomous navigation in challenging environments. Full article

This article reviews recent advances in microwave and radar techniques for non-contact measurement of human vital signs in dynamic conditions. The focus is on solutions that work when the subject is moving or performing everyday activities, rather than lying motionless in clinical settings. This review covers innovative biodegradable and flexible antenna designs for wearable devices operating in multiple frequency bands and supporting efficient 5G/IoT connectivity. Particular attention is paid to ultra-wideband (UWB) radar, Doppler sensors, and microwave reflectometry combined with advanced signal-processing and deep learning algorithms for robust estimation of respiration, heart rate, and other cardiopulmonary parameters in the presence of body motion. Applications in telemedicine, home monitoring, sports, and search and rescue are discussed, including localization of people trapped under rubble by detecting their vital sign signatures at a distance. This paper also highlights key challenges such as inter-subject anatomical variability, motion artifacts, hardware miniaturization, and energy efficiency, which still limit widespread deployment. Finally, related developments in microwave imaging and early detection of pathological tissue changes are briefly outlined, highlighting the shared components and processing methods. In general, microwave techniques show strong potential for unobtrusive, continuous, and environmentally sustainable monitoring of human physiological activity, supporting future healthcare and safety systems. Full article

This work presents an experimental evaluation of a high-speed analog-to-digital conversion method based on passive reference waveform crossings combined with time-to-digital converter (TDC) time-tagging. Unlike conventional level-crossing event-driven analog-to-digital converters (ADCs) that require dynamically updated digital-to-analog converters (DACs), the proposed architecture compares the input waveform against a broadband periodic sampling function without active threshold control. Crossing instants are detected by a high-speed comparator and converted into rising and falling edge timestamps using a multi-channel TDC. A commercial ScioSense GPX2-based time-tagger with 30 ps single-shot precision was used for validation. A range of test signals—including 5 MHz sine, sawtooth, damped sine, and frequency-modulated chirp waveforms—were acquired using triangular, sinusoidal, and sawtooth sampling functions. Stroboscopic sampling was demonstrated using reference frequencies lower than the signal of interest, enabling effective undersampling of periodic radio frequency (RF) waveforms. The method achieved effective bandwidths approaching 100 MHz, with amplitude reconstruction errors of 0.05–0.30 RMS for sinusoidal signals and 0.15–0.40 RMS for sawtooth signals. Timing jitter showed strong dependence on the relative slope between the acquired waveform and sampling function: steep regions produced jitter near 5 ns, while shallow regions exhibited jitter up to 20 ns. The study has several limitations, including the bandwidth and dead-time constraints of the commercial TDC, the finite slew rate and noise of the comparator front-end, and the limited frequency range of the generated sampling functions. These factors influence the achievable timing precision and reconstruction accuracy, especially in low-gradient signal regions. Overall, the passive waveform-crossing method demonstrates strong potential for wideband, sparse, and rapidly varying signals, with natural scalability to multi-channel systems. Potential application domains include RF acquisition, ultra-wideband (UWB) radar, integrated sensing and communication (ISAC) systems, high-speed instrumentation, and wideband timed antenna arrays. Full article

A compact high-gain antipodal Vivaldi antenna with ultra-wideband (UWB) performance ranging from 1 GHz to 25 GHz is proposed and demonstrated. The antenna features two sets of tapered exponential slots along the flare edges to enhance low-frequency impedance matching and broaden the operating bandwidth. To address high-frequency gain degradation, a rhombus-shaped metamaterial array is embedded within the tapered slot region, effectively improving radiation directivity and suppressing gain roll-off without enlarging the antenna footprint. Full-wave simulations and experimental measurements confirm that the proposed antenna achieves a well-matched impedance bandwidth from 1 to 25 GHz, with a peak gain of 15.84 dBi. Notably, the gain remains consistently above 14 dBi in the high-frequency region, verifying the effectiveness of the embedded metamaterial structure. The proposed design successfully balances wideband operation, high gain, and compact form factor, offering a promising solution for space-constrained UWB applications in communication, sensing, and imaging systems. Full article

The Dolph–Chebyshev synthesis method provides a theoretically optimal amplitude distribution for sidelobe level (SLL) minimization in narrowband antenna arrays. However, existing literature lacks systematic methodologies for adapting this classical technique to ultrawideband (UWB) systems, where fundamental assumptions—such as constant electrical spacing and frequency-independent element patterns—are severely violated. Previous UWB implementations report fractional bandwidths below 25% without detailed optimization procedures for wider bandwidths. This paper addresses this gap by presenting a comprehensive two-phase iterative optimization methodology to systematically adapt Dolph–Chebyshev principles to a 34.5% fractional bandwidth (6.0–8.5 GHz). Phase 1 uses the Powell algorithm to transform theoretical amplitude ratios into practical transmission coefficient targets, accounting for mutual coupling and impedance transformation. Phase 2 then employs multi-parameter optimization of the feeding network to achieve wideband impedance matching while preserving the required amplitude distribution. Two array variants with different element spacings are designed to demonstrate methodology scalability and validate fundamental trade-offs between SLL and array compactness in UWB operation. Experimental validation confirms excellent performance, including measured |S₁₁| < −8.9 dB and gain 6.3–10.1 dBi across the 2.5 GHz band. Crucially, the measured SLL of −13.3 dB and −14.2 dB represent a 4.1–10.2 dB improvement over uniform feeding, though it falls short of the ideal −20 to −25 dB required for high-quality radar imaging, revealing fundamental physical limitations when extending narrowband synthesis methods to 34.5% fractional bandwidth systems where electrical spacing varies by 42%. This research establishes the first documented systematic methodology with complete optimization procedures and achieves the widest fractional bandwidth (34.5%) for Dolph–Chebyshev-based arrays, while explicitly identifying both capabilities (4.1–10.2 dB SLL improvement) and fundamental physical limitations (−13 to −17 dB ceiling) inherent to UWB operation. Full article

This research presents an ultra-wideband antenna array for the non-invasive early detection of brain tumors. The primary objective of this work is to evaluate the detection capabilities of a proposed Vivaldi antenna array system for identifying small and multiple brain tumors under various simulated biological conditions. The core of the system is a Vivaldi-type antenna operating from 2.4 to 17.7 GHz, configured in both two- and four-antenna arrays. A high-fidelity, seven-layer phantom model was developed to replicate brain tissue, with each layer assigned specific electromagnetic properties (relative permittivity, tangential loss) and physical thickness. The study rigorously analyzes the system’s performance in detecting tumors across diverse scenarios, including variations in phantom complexity, tumor size, permittivity, and the number of present tumors. Using the Delay and Sum algorithm for image reconstruction, the results demonstrate the system’s feasibility in detecting tumors as small as 0.625 mm in diameter. This underscores the significant potential of the proposed design as a powerful tool for non-invasive medical diagnostics. Full article

This paper presents a comprehensive study on the design, fabrication, and characterization of ultra-wideband (UWB) wide-beam dielectric resonator antennas (DRAs) using stereolithography (SLA)-based 3D printing technology. High-purity alumina ceramics were successfully fabricated through an optimized SLA process involving 80 wt.% solid loading and sintering. The proposed DRA design incorporates a vertical ground plane to achieve a compact footprint of 0.598λ₀ × 0.491λ₀ × 0.069λ₀ (where λ₀ is the wavelength corresponding to the center operating frequency of 4.15 GHz) while demonstrating an exceptional 70.59% relative bandwidth (2.75–5.75 GHz). A novel slot-loading technique was developed to correct radiation pattern distortions caused by higher-order modes, validated through both simulation and measurement. The antenna exhibits stable unidirectional radiation patterns with a wide half-power beamwidth in both the E-plane and H-plane and a gain of 2.5–5.5 dB across the operating band. This work establishes SLA as a viable manufacturing approach for high-performance RF components. Full article

To mitigate potential interference in a coexisting system, an ultra-wideband (UWB) antenna with triple-band-notched characteristics is proposed. Based on transmission line theory, three notched bands are achieved by utilizing the open- or short-circuited properties of microstrip line resonators and slot resonators. Each antenna element consists of a patch etched with three half-wavelength slots and a one-wavelength strip. Measurement results demonstrate that the antenna exhibits excellent rejection performance at the three designated frequency bands. Furthermore, the effects of array configuration and element deflection angle on mutual coupling are investigated using a 2 × 1 face-to-face multiple-in, multiple-out (MIMO) array. Finally, a two-element MIMO array with high isolation was fabricated and measured. Experimental results show that an isolation level better than 24.6 dB is maintained across the operating band. Full article

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

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