Search Results (69)

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

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

This paper presents the concept of a 2D m × n waveguide-based power combiner (PC) that is scalable with respect to the operating frequency band and number of input ports. To our knowledge, this work reports the first planar (2D) power combiner, where the input waveguide ports are distributed in two spatial dimensions to form an array, rather than arranged along a single linear (1D) axis as in conventional corporate or cascaded waveguide combiners. The novelty of the approach relies on using H-plane rectangular waveguide T-junctions and low-loss polarization twisters in between vertically stacked T-junctions to facilitate scalability. The work is motivated by the aim to coherently combine the output power of multiple modified uni-traveling carrier (MUTC) terahertz (THz) waveguide photodiodes (PDs) in a 2D array configuration. In the manuscript, the design of a 2 × 2 planar waveguide power combiner for the WR3 band (220–320 GHz) is reported, and it is also shown that this block can be further extended to m × n input ports. Full-wave numerical analysis of the proposed 2 × 2 power combiner shows a return loss of 11 dB at the output port and an average transmission coefficient of about −6.5 dB, i.e., an overall power combining efficiency of ~90%. Furthermore, to enable 2D photodiode array integration, the manuscript presents a new slot-bow tie antenna integrated MUTC photodiode for radiating the optically generated THz power from each PD vertically into the rectangular waveguide. The simulation results of reflection loss and insertion loss for the slot bow-tie antenna are shown to be better than 10 dB and 1.4 dB over the full WR3 band, respectively. To prove scalability of the power combiner concept w.r.t. the number of input ports, a 2 × 4 power combiner is also analyzed. Results reveal a return loss better than 10 dB from 225 to 318 GHz and a transmission coefficient of approximately −9.7 dB at 300 GHz, i.e., a power combining efficiency of ~85%. Full article

This study presents a novel beam-scanning ground-penetrating radar (BS-GPR) system based on a wide-angle beam-scanning antenna array, aimed at extending the lateral detection range and improving the imaging fidelity without increasing the size of the transceiver antennas. The BS-GPR comprises a signal transceiver, a wide-angle beam-scanning antenna array for transmission and a bowtie antenna for reception. Unlike conventional commercial ground-penetrating radar (GPR), the transmitting signal of the wide-angle beam-scanning antenna array designed in this study can cover a fan-shaped region of ±90°, enabling the detection of abnormal targets outside the rectangular region directly below it. In field tests on air and sand, the BS-GPR proposed in this study can detect anomalous targets in the 55° and 30° directions, respectively. In brief, this study confirms the effectiveness of the wide-angle beam-scanning antenna array for extending the lateral detection range of GPR. Full article

This work presents the fabrication and characterization of a bow-tie antenna integrated uni-traveling carrier photodiode (UTC-PD) on a silicon carbide (SiC) substrate for efficient terahertz (THz) wave generation. The proposed device exploits the superior thermal conductivity and mechanical robustness of SiC to overcome the self-heating limitations associated with conventional indium phosphide (InP)-based photodiodes. An epitaxial layer transfer technique was utilized to bond InP/InGaAs UTC-PD structures onto SiC. The study systematically examines the influence of critical geometric parameters, specifically the mesa diameter and length between the antenna arms, on the emitted THz intensity in the 300 GHz frequency band. Experimental results show that the THz radiation efficiency is primarily governed by the mesa diameter, reflecting the trade-off between light absorption, device capacitance, and bandwidth, while the length between the antenna arms exhibits only a weak influence within the investigated parameter range. The fabricated device demonstrates strong linearity between photocurrent and THz output power up to 7.5 mA, after which saturation occurs due to space-charge effects. This work provides crucial insights for optimizing SiC-based bow-tie antenna integrated UTC-PD devices to realize robust, high-power THz sources vital for future high-data-rate wireless communication systems such as beyond 5G and 6G networks. Full article

This paper presents the novel design of a printed, low-cost, dual-port, and dual-polarized slot antenna for microwave biomedical radars. The butterfly shape of the radiating element, with orthogonally positioned arms, enables simultaneous radiation of both vertically and horizontally polarized waves. The antenna is intended for full-duplex in-band applications using two mutually isolated antenna ports, with the CPW port on the same side of the substrate as the slot antenna and the microstrip port positioned orthogonally on the other side of the substrate. Those two ports can be used as transmit and receive ports in a radar transceiver, with a port isolation of 25 dB. Thanks to the bow-tie shape of the slots and an additional coupling region between the butterfly arms, there is more flexibility in simultaneous optimization of the resonant frequency and input impedance at both ports, avoiding the need for a complicated matching network that introduces the attenuation and increases antenna dimensions. The advantage of this design is demonstrated through the modeling of an eight-element dual-port linear array with an extremely simple feed network for high-gain biosensing applications. To validate the simulation results, prototypes of the proposed antenna were fabricated and tested. The measured operating band of the antennas spans from 2.35 GHz to 2.55 GHz, with reflection coefficients of less than—10 dB, a maximum gain of 8.5 dBi, and a front-to-back gain ratio that is greater than 15 dB, which is comparable with other published single dual-port slot antennas. This is the simplest proposed dual-port, dual-polarization antenna that enables straightforward scaling to other frequency bands. Full article

This systematic review explores recent advancements in antenna and rectifier systems for radio frequency (RF) energy harvesting within the gigahertz frequency range, aiming to support the development of sustainable and efficient low-power electronic applications. Conducted under the PRISMA methodology, our review filtered 2465 initial records down to 80 relevant studies, addressing three research questions focused on antenna design, operating frequency bands, and rectifier configurations. Key variables such as antenna type, resonant frequency, gain, efficiency, bandwidth, and physical dimensions were examined. Antenna designs including fractal, spiral, bow-tie, slot, and rectangular structures were analyzed, with fractal antennas showing the highest efficiency, while array antennas exhibited lower performance despite their compact dimensions. Frequency band analysis indicated a predominance of 2.4 GHz and 5.8 GHz applications. Evaluation of substrate materials such as FR4, Rogers, RT Duroid, textiles, and unconventional composites highlighted their impact on performance optimization. Rectifier systems including Schottky, full-wave, half-wave, microwave, multi-step, and single-step designs were assessed, with Schottky rectifiers demonstrating the highest energy conversion efficiency. Additionally, correlation analyses using boxplots explored the relationships among antenna area, efficiency, operating frequency, and gain across design variables. The findings identify current trends and design considerations crucial for enhancing RF energy harvesting technologies. Full article

This paper presents a comparative analysis of performance for several antenna prototypes using a screen-printing process. This analysis was performed using various bow-tie antenna configurations, including single-band and multi-band antennas with linear or circular polarization over multiple operating frequency ranges. For antenna implementations, three different conductive inks and two resolutions of screen masks were tested. The performance of the fabricated prototypes has then been compared to the copper laser-etched antennas. This study revealed that with the proper selection of ink thinness, screen-printed bow-tie antennas achieve similar performances to copper laser-etched bow-tie antennas up to 6 GHz, even for linearly polarized and circularly polarized antennas. However, the printing resolution should be improved by reducing the ink thickness for bow-tie antennas at higher operating frequencies. The measurement results show a successful agreement after improving the printing resolution of the fabricated 5.8 GHz and 15 GHz bi-band bow-tie antennas. Full article

To enhance the capability of a ground penetrating radar (GPR) in subsurface target identification and improve its polarization sensitivity in detecting underground linear objects, a circularly polarized broadband composite spiral antenna was designed. This antenna integrates equiangular spiral and Archimedean spiral structures, achieving a wideband coverage of 1–5 GHz with stable circular polarization characteristics. The antenna employs an exponentially tapered microstrip balun for impedance matching and a metallic-backed cavity filled with absorbing materials to enhance its directivity. Experimental results demonstrate excellent radiation performance and stable circular polarization characteristics, with the axial ratio consistently below 3 dB throughout the operating frequency band, highlighting its suitability for polarimetric GPR systems. Furthermore, a 3D GPR measurement using the designed antenna validates its improved capacity for detecting subsurface linear objects, compared to the conventional linearly polarized bowtie antenna. Full article

This paper presents a circularly polarized on-chip antenna (OCA) operating in the D-band for a fully integrated bidirectional transceiver in TSMC 40 nm bulk CMOS process. Circular polarization is achieved by arranging two pairs of antennas in an orthogonal configuration. The target design at 145 GHz features a compact hybrid structure that integrates a bowtie antenna with a PCB package. This configuration not only shields the antenna from environmental interference but also improves its radiation efficiency. The proposed OCA demonstrates a simulated gain of −1.4 dBi and a radiation efficiency of 32% at 145 GHz, along with a compact footprint of 0.4 × 0.4 mm². To further enhance radiation efficiency and gain, the antenna elements are integrated into chip arrays. The OCA design presented in this work addresses key objectives in system design, including compactness, cost-effectiveness, and compatibility with existing technologies. Full article

The literature reports highlight the transmission field (B₁⁺) uniformity and efficiency constraints of cardiac magnetic resonance imaging (MRI) at ultrahigh magnetic fields (UHF). This simulation study proposes a 3D Metamaterial (MM) to address these challenges. The study proposes a 3D MM consisting of unit cells (UC) with split ring resonator (SRR) layers immersed in dielectric material glycerol. Implementing the proposed MM design aims to reduce the effective thickness and weight of the dielectric material while shaping B₁⁺ and improving the penetration depth. The latter is dictated by the chosen array size, where small local UC arrays can focus B₁⁺ and larger UC arrays can increase the field of view, at the cost of a lower penetration depth. Designing RF antennas that can effectively transmit at 21.0 T while maintaining patient safety and comfort is challenging. Using Self-Grounded Bow-Tie (SGBT) antennas in conjunction with the proposed MM demonstrated enhanced B₁⁺ efficiency and uniformity across the human heart without signal voids. The study employed dynamic parallel transmission with tailored kT points to homogenize the 3D flip angle over the whole heart. This proof-of-concept study provides the technical foundation for human cardiac MRI at 21.0 T. Such numerical simulations are mandatory precursors for the realization of whole-body human UHF MR instruments. Full article

In this paper, a planar, bow-tie antenna with an enhanced bandwidth and a bi-directional radiation pattern is proposed. The concept of multi-resonance is applied by implementing the superposition of three different bow-tie components with various radii and flare angles in an overlapped fashion into a single element, resulting in a significant increase in bandwidth. The antenna has an electrical size, kr, of 1.10, calculated at the lowest frequency of operation. The proposed antenna is simulated, and a prototype is fabricated for verification by measurement. The result is a wide −10 dB bandwidth of 80.3% (1.23–2.88 GHz) from the measurements. The antenna also maintains a bi-directional radiation pattern, with a negligible difference between the forward and backward realized gains, within the entire −10 dB bandwidth. The measured realized gain values in the forward and backward directions are between 1.5 dBi and 3.7 dBi over the −10 dB bandwidth. The comparison of the measurement and simulation results shows good agreement. Full article

This study presents a compact and stable gain spacecraft antenna that operates in all Global Navigation Satellite System (GNSS) bands from 1.164 GHz to 1.610 GHz. The proposed antenna structure based on the single-feed crossed bowtie antenna concept consists of four triangular patches excited with a 90° phase difference in between to generate right-hand circular polarization (RHCP), without needing complex feed networks. The radiator part of the antenna is covered by a radome and is also supported by a cylindrical dielectric cavity frame (DCF) to weaken the diffracted waves propagating along the ground plane while increasing vibration resistance. The fabricated antenna provides a return loss better than 10 dB with lower than 3 dB axial ratio and a stable gain around 7.2 ± 0.3 dBic over the entire GNSS bands, as well as a more compact and lightweight structural performance. It is also verified that the structural integrity and functional performance of the fabricated antenna remain consistent despite exposure to an equivalent vibration level in the launch process. The presented all-band spacecraft GNSS antenna is an innovative implementation with space industry insight for multi-band space applications that have application-specific limitations and provides consistent performance, as well as operational safety with the antenna design simplicity. Full article

A crossed bow-tie antenna design for S- and C-Band (2.44–7.62 GHz) with a peak gain of 7.29 dBi is presented to achieve wideband radiation efficiency greater than 90% and circular polarization with a single feed point. The polarization of the antenna is modeled by the input admittance of crossed bow-ties, and the model predictions are validated by experiments. A wideband matching network is designed to be tightly integrated with the antenna and produce a 103% impedance bandwidth. The matching network is decomposed into an equivalent circuit model, and an analysis is presented to demonstrate the principles of the matching network design. A prototype of the optimized antenna design is fabricated and measured to validate the analysis. Full article

Thermal Magnetic Resonance (ThermalMR) integrates Magnetic Resonance Imaging (MRI) diagnostics and targeted radio-frequency (RF) heating in a single theranostic device. The requirements for MRI (magnetic field) and targeted RF heating (electric field) govern the design of ThermalMR applicators. We hypothesize that helmet RF applicators (HPA) improve the efficacy of ThermalMR of brain tumors versus an annular phased RF array (APA). An HPA was designed using eight broadband self-grounded bow-tie (SGBT) antennae plus two SGBTs placed on top of the head. An APA of 10 equally spaced SGBTs was used as a reference. Electromagnetic field (EMF) simulations were performed for a test object (phantom) and a human head model. For a clinical scenario, the head model was modified with a tumor volume obtained from a patient with glioblastoma multiforme. To assess performance, we introduced multi-target evaluation (MTE) to ensure whole-brain slice accessibility. We implemented time multiplexed vector field shaping to optimize RF excitation. Our EMF and temperature simulations demonstrate that the HPA improves performance criteria critical to MRI and enhances targeted RF and temperature focusing versus the APA. Our findings are a foundation for the experimental implementation and application of a HPA en route to ThermalMR of brain tumors. Full article