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The letter presents a method of frequency to time domain conversion of Scattering Parameter data for microwave imaging applications. The time to frequency domain conversion was initially tested in the MATLAB. The testing was conducted in a realistic microwave imaging environment with an antenna and a heterogeneous breast phantom. Note that, the time domain signal obtained from the Vector Network Analyzer (VNA) as well as the time domain signal obtained with the introduced process is similar indicating efficiency of the proposed method. An ultra‐wideband (UWB) signal is transmitted from the transmitting Antipodal Vivaldi Antenna to the breast phantom and the received signals are collected by the same antenna over a monostatic process. A total of 36 antenna rotations were considered while scanning the phantom from various orientations. All the data stored in the VNA is extracted and the proposed frequency to time domain conversion technique was applied to it. Finally, the Delay and Sum beamforming algoirithm was used to reconstruct the target image. [ABSTRACT FROM AUTHOR]

This work presents a flat‐gain antipodal Vivaldi antenna (AVA) for ultra‐wideband (UWB) microwave imaging applications. The proposed antenna demonstrates measured and simulated impedance bandwidth from 2.3 GHz to 20 GHz with a flat gain over the band, with minimum gain variation of 2.9 dBi. The antenna is tested initially for its practical utility by measuring its specific absorption rate (SAR) value. The SAR value is observed in the simulator by modeling a realistic homogeneous as well as a heterogeneous breast phantom. The SAR value obtained complies with both American and European standards when averaged over 1 g as well as 10 g of tissue. The designed antenna is further utilized to detect multiple tumors in a realistic homogeneous and heterogeneous breast phantoms developed in the laboratory environment. The widely popular delay and sum (DAS) algorithm is utilized to reconstruct the tumor images. The imaging is done outside the anechoic chamber with an in‐house monostatic microwave imaging setup just to make it more convincing with real‐world dynamic scenario. The homogeneous phantom with four embedded tumors each of radius 4 mm and the heterogeneous phantom with two tumors, one of radius 3.5 mm and another of radius 5 mm are imaged in this work. The imaging results demonstrate that tumors of different sizes can be detected accurately in the case of both homogeneous and heterogeneous breast phantoms. AVA with an oil paper layer for bandwidth enhancement as well for achieving flat‐gain response is first of its kind to be reported in this work Also, the proposed work utilizes different phantoms for imaging several tumors of differing sizes, which has not before been described. [ABSTRACT FROM AUTHOR]

This communication presents a novel bifunctional metasurface (MS) combining the reflectarray (RA) and transmitarray (TA) with dual-band orthogonally polarized dual-beam characteristics. The proposed reflect-transmit-array (RTA) is capable of reflecting the $x$ -polarized incidence without changing its polarization state around 10 GHz while transmitting the $y$ -polarized incidence and converting it into the circularly polarized (CP) waves around 14 GHz. To completely cover the working frequency bands of both modes, an antipodal Vivaldi antenna (AVA) is introduced as the source feed due to its intrinsic ultrawideband characteristics. As a proof of concept demonstration, a prototype consisting of 20 $\times20$ elements is also designed, fabricated, and measured. We observe a good agreement between the measurement and simulation results that shows a peak gain of 26.2 dBi and 27.3 dBic, 1 dB gain bandwidth (BW) of 9.8–11.3 GHz (14.2%) and 12.8–14.2 GHz (10.4%), and peak aperture efficiency (AE) of 48.7% and 35.1% for the reflection and transmission modes, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a high-gain and ultra-wideband antipodal Vivaldi antenna (AVA) with vias-loaded linearized edges for 5G millimeter-wave applications. By replacing the traditional exponential tapered edge by linear tapered slot (LTS), the side-lobe is obviously descended. Moreover, metal vias are loaded on radiation edges, more energy in the main radiation direction is constrained and the antenna directivity and gain performance are improved. A prototype of the proposed antenna was designed, fabricated and measured. The measurements agree well with the simulations, which certify the new way for miniaturization and easier fabrication of the propose antenna. The measured results show that the antenna achieves a peak gain up to 12.1 dBi at 36 GHz and gain of 10.8 ± 1.3 dBi in the operating range from 22 to 40 GHz, where the reflection coefficient is less than −10 dB. The gain increment is up to 2 dB compared with the conventional AVA. Due to characteristics like high-gain, ultra-wideband, and compact size, it is highly well-suited for 5G millimeter-wave applications. [ABSTRACT FROM AUTHOR]

In this paper, the computational analysis for miniaturization of antipodal Vivaldi antenna (AVA) by an additional single elliptical loaded strip (SELS) is presented. The performance of the miniaturized antenna is evaluated by finite difference time domain (FDTD) technique, while its performance is also verified by finite element method (FEM). The computational time and cost of the two techniques are also compared to highlight the significance of the most suitable technique for miniaturization of the wideband antenna. It achieves ultrawideband performance with lower cutoff frequency at 0.668 GHz and 19.52 % size reduction with suitable gain performance. The proposed compact antenna exhibits good performance in the sub-GHz and ultra-wideband (UWB) frequency ranges, which makes it a suitable candidate for low power energy harvesting systems as well as for ultra-wideband applications. [ABSTRACT FROM AUTHOR]

The objective of this work is the design and validation of a directional Vivaldi antenna to detect tumor cells' electromagnetic waves with a frequency of around 5 GHz. The proposed antenna is 33% smaller than a traditional Vivaldi antenna due to the use of metamaterials in its design. It has an excellent return loss of 25 dB at 5 GHz and adequate radiation characteristics as its gain is 6.2 dB at 5 GHz. The unit cell size of the proposed metamaterial is 0.058λ × 0.054λ at the operation frequency of 5 GHz. The proposed antenna was designed and optimized in CST microwave software, and the measured and simulated results were in good agreement. The experimental study demonstrates that an array composed with the presented antennas can detect the existence of tumors in a liquid breast phantom with positional accuracy through the analysis of the minimum amplitude of Sii. [ABSTRACT FROM AUTHOR]

This research article presents a design of a wideband antipodal Vivaldi antenna (AVA) to achieve broadband performances in the millimeter wave range. The design provides excellent fractional bandwidth of 186.54% which ranges from 10.45 to above 300 GHz. It is a compact antenna that is designed by using the Fermi-Dirac function. At first, the Fermi-Dirac function is used to design an outer exponential curve. The inner curve is the quarter part of a circle. A simple but effective rectangular shaped corrugations enhancement method is also incorporated in AVA for bandwidth and gain improvement. The designed AVA is fabricated on Roger's RT/duroid 5880 substrate and its size is 30 mm × 12 mm × 0.5 mm. The corrugations improve the gain of simple Fermi-Dirac function-based AVA up to 6.76 dBi and it ranges from 7.2 to 13.1 dBi. Also, it provides a stable and an improved efficiency which is in the range of 91.5 to 97.85%. The fabricated antenna is experimentally tested to validate the simulated results. Both results are in good agreement with each other. Further, the functionality of the proposed AVA is almost stable over the desired frequency range. The designed compact AVA is very wideband antenna which gives stable radiation patterns and high gain. Hence, it is the best choice for various millimeter wave applications like 5G, radar, satellite, and medical imaging. [ABSTRACT FROM AUTHOR]

A novel high-gain filtering antipodal Vivaldi antenna based on spoof surface plasmon polariton (SSPP) structure for 5G millimeter-wave applications is proposed in this paper. By loading the metal vias (MV) on the linear tapered slot (LTS) edge, the directionality and gain are improved. Filtering performance is achieved by SSPP subwavelength structure employed on the feeding of AVA. The dimension of proposed antenna is 31.5 × 16 × 0.787 mm3. Measurements of the fabricated antenna agree well with the simulations. The measured results show that the gain of 8–12.2 dBi is realized in the wide range of 21–39 GHz, where the reflection coefficient keeps below −10 dB. The gain increment is up to 2 dBi compared with the original AVA. The low-pass filtering performance based on SSPP can effectively reduce electro-magnetic interference (EMI) effect without extending the antenna size to meet the goal of miniaturization and the better performance. [ABSTRACT FROM AUTHOR]

In this research article, a wideband antipodal Vivaldi antenna (AVA) is presented by incorporating a negative index metamaterial (NIM). The proposed antenna is designed using a linearly tapered shape structure. The overall performance of the designed antenna is improved by employing a negative index metamaterial (NIM). The 'V' shaped metamaterial unit cells are designed and placed at the top surface in between two radiators of AVA, to radiate the maximum electric field in the end-fire direction. The designed antenna dimensions are 50 mm × 24 mm × 0.51 mm and it is compact as compared to AVA antennas available in the literature. The maximum gain of the designed antenna is 15.26 dBi at 41.3 GHz. The antenna gain is almost constant and varies in the range of 9.25 ± 1.75 dBi over the operating frequency range of 15 GHz to 40 GHz. The optimized design of an antenna makes it suitable for various micrometer and millimeter wave applications. Also, the measured results matched with the simulated results. [ABSTRACT FROM AUTHOR]

Optimizing antenna parameters without knowing their impact on the gain is a time-consuming and iterative process. This article shows how the Classification and Regression Tree (CART) technique, the Random Forest (RF) algorithm, and the Principal Component Analysis (PCA) method is used to study the effect of geometrical parameters of rectangular notches of the Antipodal Vivaldi antenna on gain. Carving out the notches is a general approach for end-fire antenna design. Integrating the EM simulation with machine learning could reduce the time spent on AVA design. In this approach, the gain category of the antenna under design: Low, Medium, and High, is first classified by the three multiclass machine learning models, K-Nearest Neighbor (KNN), Artificial Neural Network (ANN), and Support Vector Machine (SVM). When the predicted category of gain belongs to the High class, in that case, the four regression models, Polynomial, SVM, ANN, and RF, predict the gain value to anticipate the antenna gain according to the notch dimensions to reduce the optimization time of the simulation-driven antenna. In this work, the band-limited approach of notches on gain is also been validated using simulation before fabrication. Machine learning models are optimized the antenna parameters to achieve a high gain within the frequency range of 20 to 40 GHz. A peak simulated gain of 19 dB is achieved at the frequency of 27 GHz. The proposed structure is fabricated utilizing a single-layer Rogers substrate (RO4003C) with a dielectric constant of 3.38 and compact dimensions of 96 mm × 174 mm × 0.508 mm, i.e., 0.32 × 0.58 × 0.0017 λ 0 3 ; here the symbol λ 0 denotes the wavelength of free space at the minimum operating frequency. [ABSTRACT FROM AUTHOR]

Ground-penetrating radar (GPR) is a widely popular sensing method with broad applications in nondestructive subsurface imaging. This article presents a multistatic GPR for vehicle-mounted roadway and utility monitoring applications that employ several methods to improve performance compared with the state of the art. The proposed system illuminates the subsurface with pseudorandom codes (m-sequences) that have near-ideal autocorrelation properties. As a result, the received signal can be matched-filtered to provide pulse compression, which improves both range resolution and depth of scan compared with impulse-based GPRs. It also uses a highly digital transmit and receive architecture based on direct FPGA-based transmit pulse generation and direct radio frequency (RF) sampling of the received echoes. Furthermore, the analog front end uses an $8 \times 8$ multistatic antenna array design with broadband antipodal Vivaldi elements to provide spatial diversity, which leads to the improved object localization and reduced drift between scans. Experimental results from indoor and outdoor test beds confirm the functionality of the proposed GPR system. [ABSTRACT FROM AUTHOR]

The gain enhanced antipodal Vivaldi antenna (AVA) is implemented in this study for fifth‐generation (5G) communication applications. At first, the conventional AVA is designed and then metamaterial and rectangular corrugations are added to AVA to enhance its gain from 7.75 to 9.53 dB. The designed antenna size is 40 mm × 24 mm × 1.6 mm and it is fabricated on the FR4 substrate. Further, modified AVA with metamaterial and corrugation increases higher cut‐off frequency from 30.62 to 34.52 GHz. The gain of the designed antenna varies between 5 and 9.53 dB over 24.77 to 34.52 GHz and its bandwidth is 9.75 GHz. The designed antenna covers 25 to 29.5 GHz and 31.8 to 33.4 GHz 5G frequency bands. Experimental results and the simulated results are nearly same, which demonstrate that the designed antenna can be used for 5G communication applications. [ABSTRACT FROM AUTHOR]

In this article, an ultra-wideband metasurface lens is designed and integrated into an antipodal Vivaldi antenna (AVA) to improve its radiation directivity without affecting its efficiency and return loss characteristics. The metasurface lens consists of high permittivity metamaterial unit cells which resonate at frequencies far away from the operation bandwidth of 1–6 GHz. Electric field distributions of the antennas show that the near-field behaves more planar for the metasurface lens loaded AVA, as compared to conventional AVA. Both the original antenna and the newly proposed antenna are simulated, fabricated, and tested. The measurements are found in very good agreement with the simulation results. In the operation bandwidth of 1–6 GHz, the return loss is less than −10 dB for both antennas. As verified by far-field measurements, the metasurface loaded AVA has achieved higher gain in the operation bandwidth. Additionally, the half power beamwidth of the AVA is significantly reduced by the inclusion of the metasurface lens. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a synthetic aperture radar (SAR)-based millimeter-wave imaging system for high-resolution imaging of human skin, in addition to traditional nondestructive testing applications. The imaging system, which operates in the 58–64-GHz frequency range, forms the basic building block of a future millimeter-wave camera suitable for imaging burned skin and skin cancers. The system is composed of a coherent transceiver and two antennas, principally enabling a quasi-monostatic measurement configuration. The designed antenna is an antipodal Vivaldi antenna with 5.0–8.0-dB gain and half-power beamwidths of ~79.0° and ~76.0°in its $E$ – and $H$ -planes, respectively. The transceiver is designed using a complete system-on-chip transmitter and receiver capable of $I/Q$ detection. The fully designed imaging system has 47 dB of dynamic range and is phase-calibrated using a robust wideband calibration procedure based on single-frequency SAR imaging approach. Examples of images produced with this system include burned pigskin skin and a small balsa wood panel with four small embedded rubber pieces. [ABSTRACT FROM AUTHOR]

In this communication, an antipodal Vivaldi antenna surrounded by dielectric (AVA-SD) is proposed for wideband applications such as microwave and millimeter-wave imaging, see-through walls, and radio astronomy. The main features of the proposed AVA-SD are wideband high gain, high front-to-back ratio, corrected the E-plane tilt of beam at wide bandwidth, narrow half-power beamwidth, and low sidelobe and cross-polarization levels. A prototype of the proposed AVA-SD is fabricated, and its performance is simulated and measured demonstrating operating frequency bandwidth from 5 to 50 GHz. The designed AVA-SD has overall size of $31.6\times110$ mm2. [ABSTRACT FROM AUTHOR]

A high-gain antipodal Vivaldi antenna with multi-layer planar dielectric lens (AVA-MPDL) is proposed. Compared to the conventional AVA design, the gain of the antenna has been greatly improved by applying the MPDL in front of the antenna’s aperture at the upper working frequencies. Additionally, beam-tilting in E-plane at higher frequencies has also been overcome. The modified antenna has been fabricated and measured, the measurement results show that the frequency band forS11 < −10 dB is from 1.3 to more than 30 GHz, and it is in good agreement with the simulated ones. Gain of the antenna has been improved by the MPDL lens in a wide frequency band (4–27 GHz) and the gain up to 16 dB at higher frequencies. [ABSTRACT FROM AUTHOR]

This communication proposes the hybrid Vivaldi-fed horn antenna, which consists of the printed antipodal Vivaldi antenna (AVA) on an FR4 substrate for better matching performance in the low-frequency band and the horn antenna that surrounds the exterior of the AVA for increased gain performance in the high frequency. In order to verify the operating principle in the low-frequency band, an equivalent circuit of the proposed antenna is modeled and analyzed. The mode decomposition technique is then used to examine the radiation physics of the proposed antenna in high-frequency band. The measured reflection coefficients in the entire frequency range are less than −3 dB of the half-power reference (maximum of −4.11 dB). The measured gains of 2.12 dBi at 1 GHz and 7.84 dBi at 6 GHz are obtained. These results confirm that the better characteristics in low-frequency matching and high-frequency gain can be achieved by the proposed design. [ABSTRACT FROM AUTHOR]

This communication presents a new approach to implement planar antipodal Vivaldi antenna design. A nature fern inspired fractal leaf structure is implemented here. Impedance bandwidth (−10 dB) of the proposed antenna is around 19.7 GHz starting from 1.3 to 20 GHz. The lower operating frequency of this antenna is reduced by 19% with the second iteration as compared to the first iteration of fractal leaf structure. The prototype antenna is fabricated and tested in frequency as well as in time domains to obtain various transfer characteristics along with common antenna parameters. Experimental results show that good wideband feature, stable radiation pattern, and promising group delay of less than 1 ns signatures are obtained, which agree well with the simulated data. The miniaturized proposed antenna structure becomes an attractive choice in microwave imaging applications because of its ultrawide fractional bandwidth at 175%, high directive gain of 10 dBi, and finally appreciably large fidelity factor above (>90%). [ABSTRACT FROM AUTHOR]

An antipodal Vivaldi antenna (AVA) with novel symmetric two-layer double-slot structure is proposed. When excited with equiamplitude and opposite phase, the two slots will have the sum vector of their E-field vectors parallel to the antenna’s plane, which is uniform to the E-field vector in the slot of a balanced AVA with three-layer structure. Compared with a typical AVA with the same size, the proposed antenna has better impedance characteristics because of the amelioration introduced by the coupling between the two slots, as well as the more symmetric radiation patterns and the remarkably lowered cross-polarization level at the endfire direction. For validating the analysis, an UWB balun based on the double-sided parallel stripline is designed for realizing the excitation, and a sample of the proposed antenna is fabricated. The measured results reveal that the proposed has an operating frequency range from 2.8 to 15 GHz, in which the cross-polarization level is less than −24.8 dB. Besides, the group delay of two face-to-face samples has a variation less than 0.62 ns, which exhibits the ability of the novel structure for transferring pulse signal with high fidelity. The simple two-layer structure, together with the improvement both in impedance and radiation characteristics, makes the proposed antenna much desirable for the UWB applications. [ABSTRACT FROM AUTHOR]

This paper presents a planar ultra–wideband Antipodal Vivaldi Antenna (AVA) working over a super ultra–wideband frequency range of 1.5–55 GHz, found to suffice for various communication standards including that of the 5G mm-Wave communication, microwave imaging, non-destructive testing, defense applications, etc. The proposed antenna, fabricated on a single layer Rogers substrate (RO4003C) having a dielectric constant of 3.38, has a compact dimension of 96 mm × 175 mm × 0.508 mm, i.e., 0. 80 × 0.875 × 0.00254 λ 0 3 , where λ 0 is the free space wavelength at the lowest frequency of operation. The designed antenna has exponential flaring and a tapered slot edge. Moreover, an elliptical parasitic patch is placed between the flares of the AVA to improve the directive gain. Dielectric lens and metasurface are used to further enhance the gain. The measured return loss, radiation pattern, and gain of the designed AVA are found to be in good agreement with the results obtained from the full-wave electromagnetic simulation. [ABSTRACT FROM AUTHOR]

We present two novel ultra-wideband (UWB) antennas embedded in a low-temperature co-fired ceramic (LTCC) package designed to house the UWB transceiver chip. Given their planar topology, circuit integration possibilities, and compact size, a partial ground-plane triangular monopole antenna (PGP-TM) and an antipodal Vivaldi antenna (AVA) are fully characterized. The performance in both the frequency and time domain are presented. The PGP-TM employs parasitic elements for tuning of the antenna's return loss. The PGP-TM antenna's measured 3.5–6.5-GHz bandwidth and omnidirectional pattern with 0-dB gain is suitable for the direct-sequence UWB (DS-UWB) lower sub-band, while the AVA's measured bandwidth of 3.35 GHz from 6.65 to 10 GHz and 5-dB gain make it suitable for the DS-UWB upper sub-band. The complete LTCC module containing the PGP-TM measures only 30 mm × 25 mm × 1.2 mm, while the AVA module measures 50 mm × 25 mm × 1.2 mm. Both LTCC modules can accommodate transceiver electronics because of a specially designed circuit feature. The effects of path loss can be canceled by combining these antennas in a transmission system. These are believed to be the first demonstrations of system-in-package technology for UWB applications. [ABSTRACT FROM AUTHOR]

This paper presents a compact 1 × 4 antipodal Vivaldi antenna (AVA) array for 5G millimeter-wave applications. The designed antenna operates over 24.19 GHz–29.15 GHz and 30.28 GHz–40.47 GHz frequency ranges. The proposed antenna provides a high gain of 8 dBi to 13.2 dBi and the highest gain is obtained at 40.3 GHz. The proposed antenna operates on frequency range-2 (FR2) and covers n257, n258, n260, and n261 frequency bands of 5G communication. The corrugations and RT/Duroid 5880 substrate are used to reduce the antenna size to 24 mm × 28.8 mm × 0.254 mm, which makes the antenna highly compact. Furthermore, the corrugations play an important role in the front-to-back ratio improvement, which further enhances the gain of the antenna. The corporate feeding is optimized meticulously to obtain an enhanced bandwidth and narrow beamwidth. The radiation pattern does not vary over the desired operating frequency range. In addition, the experimental results of the fabricated antenna coincide with the simulated results. The presented antenna design shows a substantial improvement in size, gain, and bandwidth when compared to what has been reported for an AVA with nearly the same size, which makes the proposed antenna one of the best candidates for application in devices that operate in the millimeter frequency range. [ABSTRACT FROM AUTHOR]