Search Results (68)

In this study, a novel improved ultra-wideband (UWB) antipodal Vivaldi antenna suitable for breast cancer detection via microwave imaging was designed. The antenna was made more directional by adding three pairs of nestings to the antenna fins by adding elliptical patches. The frequency operating range of the proposed antenna is UWB 3.6–13 GHz, its directivity is 11 dB, and its gain is 9.27 dB. The antenna is designed with FR4 dielectric material and dimensions of 34.6 mm × 33 mm × 1.6 mm. It was demonstrated that the bandwidth, gain, and directivity of the proposed antenna meet the requirements for UWB radar applications. The Vivaldi antenna was tested on an imaging system developed using the CST Microwave Studio (CST MWS) program. In CST MWS, a hemispherical heterogeneous breast model with a radius of 50 mm was created and a spherical tumor with a diameter of 0.9 mm was placed inside. A Gaussian pulse was sent through Vivaldi antennas and the scattered signals were collected. Then, adaptive Wiener filter and image formation algorithm delay-multiply-sum (DMAS) steps were applied to the reflected signals. Using these steps, the tumor in the breast model was scanned at high resolution. In the simulation application, the tumor in the heterogeneous phantom was detected and imaged in the correct position. A monostatic radar-based system was implemented for scanning a breast phantom in the prone position in an experimental setting. For experimental measurements, homogeneous (fat and tumor) and heterogeneous (skin, fat, glandular, and tumor) breast phantoms were produced according to the electrical properties of the tissues. The phantoms were designed as hemispherical with a diameter of 100 mm. A spherical tumor tissue with a diameter of 16 mm was placed in the phantoms produced in the experimental environment. The dynamic range of the VNA device used allowed us to image a 16 mm diameter tumor in the experimental setting. The developed microwave imaging system shows that it is suitable for the early-stage detection of breast cancer by scanning the tumor in the correct location in breast phantoms. Full article

We propose a new ultra-wideband antipodal Vivaldi antenna design based on the Klopfenstein curve, incorporating exponential slots, horns, and apertures to improve the antenna’s return loss and increase its gain in high-frequency bands. The antenna achieves high gain and wide bandwidth characteristics, with measured −10 dB bandwidth ranging from 2 GHz to 20 GHz, maximum gain of 14 dBi, and gain exceeding 10 dBi from 3.5 GHz to 14 GHz. Full article

The impact of breast cancer on public health is serious, and due to risk/benefit assessment, screening programs are usually restricted to women older than 49 years. Microwave imaging devices offer advantages such as non-ionizing radiation, low cost, and the ability to distinguish between cancerous and healthy tissues due to their electrical properties. Ensuring the safety of this technology is vital for its potential clinical application. To estimate the temperature increase in breast tissues from a microwave imaging scanner, cases of healthy, benign, and malignant breast tissues were analyzed using three digital models and adding two healthy breast models with varying densities. Virtual experiments were conducted using the Sim4Life software (version 7.2) with a system consisting of a horn antenna in transmission and a Vivaldi antenna in reception. Temperature increases were estimated based on the Specific Absorption Rate distributions computed for different configurations and frequencies. The highest temperature increase obtained in this analysis is lower than 60 μK in fibroglandular tissue or skin, depending on the frequency and breast density. The presence of a receiving antenna acting as a scatterer modifies the temperature increase, which is almost negligible. Microwave examination can be performed without harmful thermal effects due to electromagnetic field exposure. Full article

Peanut quality, with the defect rate as a critical determinant, has a profound impact on its market value. In this study, we introduce an innovative non-destructive evaluation method for peanut defects. Differing from traditional and often expensive or complex detection methods, our approach utilizes a low-cost antipodal Vivaldi antenna, complemented by a custom-designed defect rate detection system. Prior to experimentation, we simulated the antenna and system architecture to ensure their operational efficiency, a step that not only conserves resources but also validates the reliability of subsequent results. We conducted experimental tests on fresh peanut pods, obtaining electromagnetic scattering parameters (S₁₁ and S₂₁ magnitudes/phases within 1–2 GHz) through non-destructive measurements. These parameters were used as input features, while the defect rate served as the output variable. By implementing the XGBoost algorithm, we established predictive models for defect rate quantification (regression) and defect grade classification. In comparison to some traditional statistical models, such as linear regression, which may struggle with non-linear data patterns, XGBoost effectively modeled the complex relationship between the scattering parameters and the defect rate. Experimentally, the regression model achieved an R² value of 0.8113 for defect rate prediction, and the classification model reached an accuracy of 0.7526 in grading defect severity. The entire device, costing less than USD 50, provides a significant cost advantage over many commercial systems. This low-cost setup enables real-time evaluation of peanut pod defects and efficiently categorizes the defect rate without the time-consuming sample preparation and tiling operations required by traditional image-based inspection methods. As a result, it offers an affordable and practical solution for quality control in peanut production, showing great potential for wide application in the peanut industry. Full article

RFID technology has been widely researched and used for structural health applications because of its compact, wireless, and scalable nature. This technology is divided into chipped and chipless sensors. Chipped sensors are costly due to their chipped tags, have narrowband operations, and contribute to shortcomings in detection capability. Chipless tags provide real-time monitoring of cracks in harsh environments like high-temperature areas and high electromagnetic interference areas. This paper presents a design of a novel chipless hybrid circular-hexagon sensor that uses the frequency signature-based method for metal crack detection and characterization using wideband frequency. This sensor is small in size (16 mm × 16 mm × 1.4 mm) and easily mountable in hard-to-reach areas. It is a low-cost, passive chipless sensor that can wirelessly monitor the cracks in metallic structures. The radar cross-section of the chipless tag shows a shift in the resonant frequency of the tag under crack and no crack conditions. Key contributions of this work are that through simulations and experimental investigation, the tag is shown to be able to detect mm-scale cracks, validating the concept and correlating the presence and size of the cracks based on the shift in resonant frequencies in which a pair of Vivaldi antennas are used as a transmitter and receiver to connect to the VNA. The designed small sensor tag is tested in a benchtop setup with no prior calibration, imitating the real-time environment conditions for crack detection. Full article

In this paper, the performance, advantages and challenges of polymer microwave fibers (PMF) for sub-THz links are evaluated first. Then, a simple and elegant transceiver-integrated circuit (IC) and PMF wireless coupling scheme is presented. The proposed solution utilizes an advanced IC packaging technology to implement a Vivaldi antenna-in-package (AiP). The antenna is designed to provide lateral radiation and excellent directivity, so the proposed solution is very simple, compact, robust and cost-efficient: the IC readily connects to the PMF and the coupling is merely achieved by the packaged IC, without the need for any extra interface. The system operates at around 140 GHz, achieving a coupling loss of just 3.5 dB. Full article

This paper proposes a dual-band co-aperture antenna, which covers 2.09–11.61 GHz (9.52 GHz, 138.9%) and 21.6–29.6 GHz (8 GHz, 31%). The overall size of the proposed antenna is 0.76 × 0.76 × 0.37 λ₀³, where λ₀ is the free space wavelength of the lowest operating frequency of 2.09 GHz. By removing the internal metal of the monopole antenna and adding a Vivaldi antenna at the bottom of the bowl monopole antenna, dual-band radiation characteristics can be achieved. A medium polarization converter is used to achieve circular polarization and improve the broadside gain in the high-frequency band. The simulation results show that the antenna has a stable omnidirectional radiation pattern in the low-frequency band and a directional radiation pattern in the high-frequency band. Full article

Due to the high gain, wide bandwidth, and directional radiation characteristics of Vivaldi antennas, this paper conducted relevant research on the feasibility of non-destructive blood glucose detection based on Vivaldi antennas. The research included finite element method (FEM) simulation and glucose concentration monitoring. In the simulation stage, the power transmission and reflection characteristics, radiation characteristics, and electric field distribution characteristics of the antenna were described in detail. In the test stage, the S₁₁ response of the antenna to variation in glucose concentration in the range of 0–6.11 mg/mL was measured, including the S₁₁ amplitude and phase. The experimental results show that there is a high linear correlation between the S₁₁ response and glucose concentration, and the sensitivity of the S₁₁ amplitude response to the variation in glucose concentration is close to 0.3445 (dB/(mg/mL)) at 14.2556 GHz, and the sensitivity of the S₁₁ phase response to the variation in glucose concentration is about 0.5652 (degree/(mg/mL)) at 14.37 GHz. In addition, the predicted results of the glucose concentration based on linear regression are discussed. Full article

This paper analyzes broadband antennas, with a special focus on Vivaldi antennas, for their suitability for through-wall radar applications. It assesses various antenna designs, emphasizing high gain, wide impedance bandwidth, and effective wall penetration capabilities. Vivaldi antennas are superior due to their broad bandwidth, high gain, and directional radiation patterns. This study further explores structural optimizations, feeding techniques, and performance enhancement strategies to refine Vivaldi antenna designs for through-wall radar systems. Through a comparative analysis and technical evaluation, this paper highlights Vivaldi antennas’ potential for improving through-wall radar systems’ imaging and sensing capabilities. This presents a pathway for future ultra-wideband advancements. Full article

This paper proposes a novel feed array antenna to achieve a uniform electric field distribution in the near-field region for feeding a large-aperture antenna. The feed antenna has a 4 × 4 rectangular array configuration to obtain uniform near-field distribution on a virtual target surface. Each element of the array consists of a Vivaldi radiator and parasitic rings, and these two components have different radiating modes. In particular, the near-field pattern of the parasitic rings can be varied by adjusting their radii. Thus, the required near-field distribution on the virtual target surface can be achieved by optimizing the radii of the parasitic rings. To further enhance the uniformity of the electric field, the input phase of each Vivaldi radiator is adjusted by applying different transmission line lengths to the Vivaldi radiators depending on their positions in the array. To verify the feasibility of the proposed antenna, the electric field distributions are measured in an electromagnetic anechoic chamber. The results demonstrate that the proposed feed array antenna can achieve uniform near-field distribution with an average of 1.7 dB and a deviation of 6.8 dB on the virtual target surface placed within half a wavelength from the antenna aperture. Full article

This paper demonstrates the design steps of a slot-loaded Vivaldi antenna for biomedical microwave imaging applications, showing the influence of the design parameters on the antenna’s dimensions and performances. Several antenna miniaturization techniques were taken into consideration during the design: reduction in the electromagnetic wavelength by using a high-permittivity substrate material (relative permittivity ${ϵ}_r=10.2$), the placement of the antenna inside a coupling medium (${ϵ}_r=23$), and the elongation of the current path by etching slots on each side of the radiator to reduce the antenna’s lowest resonant frequency without increasing its physical dimensions. Moreover, an analysis of different antenna slot design scenarios was performed considering different slot lengths, inclination angles, positions, and numbers. Considering the frequency range of microwave imaging (i.e., about 500 MHz–5 GHz) and the array arrangement typical of microwave imaging, the best design was chosen. Finally, the antenna was fabricated and its performances in the coupling medium were characterized. The simulation and measurement results showed good agreement between each other. In comparison with literature antennas, the one developed in this work shows wide bandwidth and compact dimensions. Full article

A characterization of near-field impulse responses based on electromagnetic (EM) near-field data from an EM solver to explore features of the propagation process on a well-known wideband traveling wave antenna—double-slot Vivaldi antenna—is presented in this article. The intensity, propagating time and partitional response characteristics facilitate interpretation of the propagation process and impacts of the antenna partitions on the process. The EM energy flows guided, reoriented and scattered along a sequence of antennas transmitting and radiating segments were recognized. The geometric features of near-field wavefront surfaces supported evaluation of the EM flow proportions and antenna directivity. Impact of the structural section on radiation was also assessed by the partitional far-field response characteristic in frequency and time domains. Supported by many complementary characteristics in the analyses, inherent features of the propagation process were emphasized and false flags were minimized. By this approach, the simplification for the near-field propagation model contributed to enhancing the insight of near-field propagation processes on the double-slot antipodal Vivaldi antennas and enabled optimizing the antenna structure details. Full article

In this paper, two orthogonally placed Vivaldi antennas with a septum-like polarizer to generate circular polarized (CP) waves are presented. Septum polarizers have garnered attention due to their simple structure and high quality of CP waves. While a typical septum polarizer has been applied to various types of waveguides, its applicability to the substrate integrated Vivaldi antenna is demonstrated here for the first time. A pulse train-shaped polarizer is used, which is placed on one of the two Vivaldi antennas. The contours of the polarizer are optimized using a genetic algorithm to provide an equal amplitude and 90° phase difference between the two orthogonal electric fields. In contrast to typical feed networks with a 90° phase shifter, any unwanted loss caused by an electronic circuit can be greatly mitigated. The antenna prototype was fabricated, and its radiation pattern and impedance matching were measured and compared to the simulated results. Full article

A dual-polarized compact Vivaldi antenna with high gain performance is proposed for tree radar applications. The proposed design introduces an array configuration consisting of two pairs of two Vivaldi elements to optimize the operating bandwidth and gain while providing dual-polarization capability. To enhance the gain of the proposed antenna over a certain frequency range of interest, directors and edge slots are incorporated into each Vivaldi element. To further enhance the overall antenna gain, a metal back reflector is used. The measurement results of the fabricated antenna show that the proposed antenna achieves a high gain of 5.5 to 14.8 dBi over broadband from 0.5 GHz to 3 GHz. Moreover, it achieves cross-polarization discrimination larger than 20 dB, ensuring high polarization purity. The fabricated antenna is used to detect and image the defects inside tree trunks. The results show that the proposed antenna yields a better-migrated image with a clear defect region compared to that obtained by a commercial Horn antenna. Full article

This text proposes a Vivaldi structure array antenna, using a power divider structure. The composition includes an antenna array with four antennas, suitable for a wideband array structure antenna in the 100 GHz frequency band. The goal is to address the challenges faced by monolithic systems in modern wireless communications, particularly the issue of the inapplicability of antennas on silicon substrates. The Vivaldi antenna was chosen for its wide bandwidth, high efficiency, and stable radiation pattern. It combines the characteristics of a wide scanning angle and ultra-wide bandwidth. Through integration with CMOS technology, the developed antenna achieved a bandwidth of 85.47–102.40 GHz. The peak gain reached −4 dBi, corresponding to a bandwidth of 17.7%. And the antenna volume was only 1.2 mm × 1.2 mm, demonstrating its immense potential in high-frequency wireless applications. Full article