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An intrabody area nanonetwork (intra-BANN) is a set of nanoscale devices, which have outstanding cellular level precision and accuracy for enabling noninvasive healthcare monitoring and disease diagnosis. In this article, we design a novel feedforward neural networks (FFNNs) based data aggregation scheme that integrates the attributes of artificial intelligence to boost the computational intelligence of intra-BANNs for prolonged network lifetime. In the proposed scheme, data division and labeling are performed to transmit detected information using two different types of packets with different sizes to save energy resources and to avoid redundant data transmission. FFNN-based periodic data transmission exploits the fitness function approximation characteristics of FFNN to increase the transmission probability of critical information with minimum energy consumption and delay, whereas our proposed event-driven data transmission also ensures the transmission of high priority data with minimal delay and storage overhead. The detailed evaluation and comparison of our proposed framework with three existing schemes conducted using the Nano-Sim tool highlight that our proposed scheme performs 50%–60% better than state-of-the-art schemes in terms of residual energy, delay, and packet loss.

In this letter, a low-profile and wideband substrate integrated waveguide (SIW) antenna is proposed and validated for full-duplex systems. The proposed antenna operates at 4.9 GHz and 5.8 GHz Wireless Local Area Network (WLAN) bands. Each resonator of the antenna consists of a modified half-mode SIW (HMSIW) cavity, and excited by a 50 $\Omega$ coaxial probe. The wideband response is achieved by coupling the fundamental TE\textsubscript{10} mode with the perturbed TE\textsubscript{10} mode of the HMSIW cavity. The compactness of the proposed design is obtained using two rectangular slots near the closed-ends of the cavities. By properly optimizing the overall geometry, the proposed design exhibits a 10-dB fractional bandwidth of 8.2 \% (4.78--5.2 GHz) and 7.7 \% (5.70--6.16 GHz) in the lower (4.9 GHz) and upper frequency band (5.8 GHz), respectively. The bandwidths of both frequency bands can be controlled by adjusting the coupling between modes. A high isolation ( $>$ 30 dB) between the two ports is observed due to series of metallic vias between them. This antenna has compact size (0.34 $\lambda_{g}^{2}$ ) with high gains of 5.24 dBi and 5.37 dBi at 4.9 GHz and 5.8 GHz, respectively.

Plasmonic metasurface nanostructures have the potential to enable nonlinear optical functionality in metasurfaces by reducing power operating thresholds and enabling ultra-thin subwavelength devices. However, low absorption caused by resistive losses of unwanted metallic appearance and irregular corners in the fabrication process significantly reduces this promise, leading the metasurface community toward the new approaches to fabricate large area metasurfaces with Electron Beam lithography (EBL). In this article, with controlled proximity effect and high dose exposure rate in EBL setup, large area (2 cm2) metasurfaces are fabricated with high resolution of structure. The effect of absorption resonance in Infrared (LWIR) is experimentally studied through Fourier Transform Infrared Spectroscopy (FTIR). The results signify that the metasurface with high resolution and fine metallic corners outperforms the fabricated prototype with metal residue and non-uniform corners. When compared to conventional EBL, our nanofabrication approach speeds the patterning time by three times. The experimental measurements reveal enhanced absorption performance at 8 µm wavelength. Whereas, the developed metasurface is numerically studied to explain the absorption performance with plasmonic field distributions. This approach could be used in optoelectronic devices involving plasmonic applications, such as biosensing and infrared imaging.

In this article, a four-element circularly polarized series-slot-fed multiple–input-multiple-output (MIMO) antenna array with circular polarization (CP) diversity is presented. The proposed design utilizes a combination of 45° inclined slots and a straight microstrip line feeding technique. The two antennas are designed to operate with the opposite sense of CP. CP is achieved by placing a patch of just about square dimensions on the top of the V-slot with orthogonal but unequal arms. The unequal arm of the slot degenerates the fundamental mode at a slightly different frequency with a 90° phase difference occurring at the center frequency of each arm. Proper positioning of the patch on the top of the slot ensures excitation of CP. For realizing a MIMO antenna with a different sense of polarization, both the slots and the patches are flipped with respect to the feedline. Following optimization at the full-wave level of description, the antenna is prototyped and validated experimentally. The realizable antenna footprint is 20 mm $\times27.7$ mm. The simulated and measured results indicate that the proposed antenna features a wide impedance bandwidth ( $\vert \text{S}_{11}\vert dB) from 26.9 to 30.7 GHz, 3 dB axial ratio bandwidth from 27.31 to 29.65 GHz and the peak realized gain of 11.86 dBic. Moreover, it exhibits a low level of in-band isolation $\vert \text{S}_{21}\vert > -37$ dB and an almost negligible envelope correlation coefficient (ECC), less than 0.00025. The highly directional beams, high gain, and compact size of the proposed antenna permit implementation of multiple antennas for indoor applications in the 28 GHz band.

In this paper, a high-performance antenna-on-chip (AoC) is implemented on gallium arsenide (GaAs) wafer based on the substrate integrated waveguide (SIW) and metasurface (MTS) technologies for terahertz band applications. The proposed antenna is constructed using five stacked layers comprising metal-GaAs-metal-GaAs-metal. The conductive electromagnetic radiators are implemented on the upper side of the top GaAs layer, which has a metallic ground-plane at its underside. The metallic feedline is implemented at the underside of the bottom GaAs layer. Dual wrench-shaped radiators are framed by metallic vias connected to the ground-plane to create SIW cavity. This technique mitigates the surface waves and the substrate losses, thereby improving the antenna's radiation characteristics. The antenna is excited by a T-shaped feedline implemented on the underside of the bottom GaAs substrate layer. Electromagnetic (EM) energy from the feedline is coupled to the radiating elements through the circular and linear slots etched in the middle ground-plane layer. To mitigate the surface-wave interactions and the substrate losses in the bottom GaAs layer, the feedline is contained inside a SIW cavity. To enhance the antenna's performance, the radiators are transformed into a metamaterial-inspired surface (i.e., metasurface), by engraving periodic arrangement of circular slots of sub-wavelength diameter and periodicity. Essentially, the slots act as resonant scatterers, which control the EM response of the surface. The antenna of dimensions of 400 × 400 × 8 μm

This communication proposes a modified formulation of antenna parameter tuning problem. The main ingredient of the presented approach is a frequency-based regularization. It allows for smoothening the functional landscape of the assumed cost function, defined to encode the prescribed design specifications. The regularization is implemented as a special penalty term complementing the primary objective and enforcing the alignment of the antenna responses with the target operating frequency (or frequencies for multiband antennas). The result is an improved reliability and reduced cost of the optimization process, both highly desirable from the point of view of the efficacy of electromagnetic (EM)-driven design procedures. Furthermore, regularization makes the use of local routines sufficient even in situations where the global search is otherwise imperative (e.g., due to poor initial design). Our methodology is demonstrated using three microstrip antennas. The superior performance of the approach, both in terms of design reliability and in terms of the computational cost of the optimization process, is corroborated by comparisons with a conventional formulation.

This article proposes an efficient and complete wireless power transfer (WPT) system (WPTS) for multipurpose biomedical implants. The WPTS is composed of a self-diplexing implantable antenna, efficient rectifier, and WPT transmitter (WPT Tx). The proposed system is capable of simultaneously transmitting recorded data and recharging the batteries of the devices (so as to elongate the implant life). The WPT Tx occupies dimensions of $50 \times 50 \times 1.6$ mm3 and is optimized to effectively transfer power at 1470 MHz to a 55-mm deep implantable device. An efficient and compact ( $3.4 \times 6.7$ mm2) rectifier is used at 1470 MHz to convert the harvested RF power into a useful direct current (dc) power. The proposed rectifier circuit exhibits a high conversion efficiency of 50% even at an input power of −14 dBm and maximum efficiency of 76.1% at 2 dBm. The proposed self-diplexing implantable antenna occupies small dimensions (9.4 mm3) and operates at 915 and 1470 MHz by exciting ports 1 and 2, respectively. The biotelemetry operation is performed using a 915 MHz band (port 1), and the rectifier circuit is connected to port 2 (1470 MHz) to perform wireless powering. The simulated results are validated by examining the individual elements (WPT Tx, rectifier, and self-diplexing antenna) and overall WPTS in a saline solution and minced pork. The results prove that the proposed scheme is suitable for biotelemetry and wireless powering of biomedical implants.

A highly compact substrate integrated waveguide (SIW) self-diplexing antenna, operating at wireless local area network bands (3.6 and 5.4 GHz), is proposed in this letter. The proposed antenna consists of two closely placed (0.022 $\lambda _{g}$ , where $\lambda _{g}$ is the guided wavelength at 3.6 GHz) quarter-mode SIW resonators, exited by two coaxial probes. Two rectangular slots are added to the closed-ends of each resonator to generate additional capacitances. Therefore, both resonators operate below their fundamental frequencies, and hence, miniaturization is achieved. Moreover, a reliable circuit model is developed to validate the design process. The proposed antenna has ultracompact dimensions of 0.08 $\lambda _{g}^{2}$ with simulated gains of 4.9 and 5.34 dBi at 3.6 and 5.4 GHz, respectively. In addition, the simulated isolation levels are 32.5 and 36.6 dB at the lower and higher resonant bands, respectively. Furthermore, both resonant frequencies can be independently controlled by changing the length of the capacitive slots. Due to its compactness, independent resonance control and high isolation, the proposed antenna is suitable for compact and planar radio frequency components.

In this paper, a coplanar waveguide-fed ultra-wideband-multiple-input and multiple-output (UWB-MIMO) antenna with a novel stub for isolation has been presented. The dimensions of the proposed antenna are 18 × 22 × 1.6 mm3. The proposed antenna is design on an FR4 substrate and simulated in CST studio. The |S11| of the presented MIMO antenna is less than −10 dB between 2.8 and 13 GHz with an impedance bandwidth of 10.2 GHz. The envelope correlation coefficient (ECC) is less than 0.007 and diversity gain (DG) is greater than 9.97 dB. The proposed UWB-MIMO antenna is analyzed in terms of isolation, reflection coefficient, current distribution, ECC, DG, peak gain, multiplexing efficiency, and radiation pattern.

The novel coronavirus-2019 (Covid-19), a contagious disease became a pandemic and has caused overwhelming effects on the human lives and world economy. The detection of the contagious disease is vital to avert further spread and to promptly treat the infected people. The need of automated scientific assisting diagnostic methods to identify Covid-19 in the infected people has increased since less accurate automated diagnostic methods are available. Recent studies based on the radiology imaging suggested that the imaging patterns on X-ray images and Computed Tomography (CT) scans contain leading information about Covid-19 and is considered as a potential automated diagnosis method. Machine learning and deep learning techniques combined with radiology imaging can be helpful for accurate detection of the disease. A deep learning approach based on the multilayer-Spatial Convolutional Neural Network for automatic detection of Covid-19 using chest X-ray images and CT scans is proposed in this paper. The proposed model, named as the Multilayer Spatial Covid Convolutional Neural Network (MSCovCNN), provides an automated accurate diagnostics for Covid-19 detection. The proposed model showed 93.63% detection accuracy and 97.88% AUC (Area Under Curve) for chest x-ray images and 91.44% detection accuracy and 95.92% AUC for chest CT scans, respectively. We have used 5-tiered 2D-CNN frameworks followed by the Artificial Neural Network (ANN) and softmax classifier. In the CNN each convolution layer is followed by an activation function and a Maxpooling layer. The proposed model can be used to assist the radiologists in detecting the Covid-19 and confirming their initial screening.

This letter presents the design of a single point-fed, geometrically simple circularly polarized (CP) antenna for 28 GHz Ka-band applications. The proposed antenna is based on a straight microstrip line printed on one side and coupled with the nearly square patches through a 45° inclined V-shaped slot aperture on the other side. In order to generate circular polarization, the fundamental radiating mode is degenerated at a slightly different frequency by aligning the patch edges parallel to each arm of the V-slot with orthogonal arms. This configuration yields a relatively small size (10 mm × 27.7 mm), wideband, and high-gain right-hand CP antenna operating at 28 GHz. The impedance bandwidth of the proposed antenna is from 27.2 to 30.35 GHz and the 3 dB axial ratio (AR) bandwidth from 27.3 to 29.7 GHz with excellent directional characteristics in the broadside direction. The peak gain is approximately 11.65 dBic. The performance characteristics in terms of the impedance matching, AR, gain, and efficiency of the antenna for wearable applications are also investigated both numerically and experimentally. For practical applications, the small size of the structure allows for implementing the systems that consist of more than one antenna to account for user mobility.

Speech enhancement is a very important problem in various speech processing applications. Recently, supervised speech enhancement using deep learning approaches to estimate a time-frequency mask have proved remarkable performance gain. In this paper, we have proposed time-frequency masking-based supervised speech enhancement method for improving intelligibility and quality of the noisy speech. We believe that a large performance gain can be achieved if deep neural networks (DNNs) are layer-wise pre-trained by stacking Gaussian-Bernoulli Restricted Boltzmann Machine (GB-RBM). The proposed DNN is called as Gaussian-Bernoulli Deep Belief Network (GB-DBN) and are optimized by minimizing errors between the estimated and pre-defined masks. Non-linear Mel-Scale weighted mean square error (LMW-MSE) loss function is used as training criterion. We have examined the performance of the proposed pre-training scheme using different DNNs which are established on three time-frequency masks comprised of the ideal amplitude mask (IAM), ideal ratio mask (IRM), and phase sensitive mask (PSM). The results in different noisy conditions demonstrated that when DNNs are pre-trained by the proposed scheme provided a persistent performance gain in terms of the perceived speech intelligibility and quality. Also, the proposed pre-training scheme is effective and robust in noisy training data.

This letter proposes a low-profile substrate integrated waveguide (SIW) cavity backed self-quadruplexing antenna for wearable transceivers. The full-mode circular SIW cavity is split into four unequal quarter-mode SIW (QMSIW) cavities using the two slots on the upper layer of the cavity. The proposed antenna uses C-shaped and arc-shaped slots of different dimensions in each QMSIW resonator to operate at wireless local area network bands (3.5, 4.9, 5.4, and 5.8 GHz). The measured gains are 4.4, 5.07, 5.40, and 5.7 dBi at 3.5, 4.9, 5.4, and 5.8 GHz, respectively. The antenna is simulated and optimized inside a 48 $\times \text{76}\times$ 21 mm3 rectangular device by keeping the device on the chest of a realistic human model. The proposed antenna has unidirectional radiation patterns in all four operating bands with low backward radiations. Thus, it has low specific absorption rate at all four operating bands.

A novel printed and compact profile monopole antenna with hybrid reconfigurability structure for switching the resonant frequency and direction of maximum radiations is proposed in this research work. A novel mathematical model for the architecture of Reconfigurable Patch Antenna (RPA), considering input impedance, bandwidth, antenna gain, antenna efficiency and resonant frequency is proposed. For the desired functionality, antenna is incorporated with three switches in such a way that Switch 1 and Switch 2 direct the radiation beam patterns towards different directions while Switch 3 controls the frequency reconfigurability. When Switch 3 is ON, the designed antenna operates at 26.4 GHz covering the 24.2–26.5 GHz band. When Switch 3 is OFF, it operates at 28 GHZ, covering the 27.4–29.8 GHz band. The antenna is proposed to operate at the 5G mobile communication band having a center frequency at 27.6 GHz with a reflection coefficient of −21.5 dB. A 3D design tool HFSS has been used for the simulation purposes.

Speech-in-noise perception is an important research problem in many real-world multimedia applications. The noise-reduction methods contributed significantly; however rely on a priori information about the noise signals. Deep learning approaches are developed for enhancing the speech signals in nonstationary noisy backgrounds and their benefits are evaluated for the perceived speech quality and intelligibility. In this paper, a multi-objective speech enhancement based on the Long-Short Term Memory (LSTM) recurrent neural network (RNN) is proposed to simultaneously estimate the magnitude and phase spectra of clean speech. During training, the noisy phase spectrum is incorporated as a target and the unstructured phase spectrum is transformed to its derivative that has an identical structure to corresponding magnitude spectrum. Critical Band Importance Functions (CBIFs) are used in training process to further improve the network performance. The results verified that the proposed multi-objective LSTM (MO-LSTM) successfully outscored the standard magnitude-aware LSTM (MA-LSTM), magnitude-aware DNN (MA-DNN), phase-aware DNN (PA-DNN), magnitude-aware GNN (MA-GNN) and magnitude-aware CNN (MA-CNN). Moreover, the proposed speech enhancement considerably improved the speech quality, intelligibility, noise-reduction and automatic speech recognition in changing noisy backgrounds, which is confirmed by the ANalysis Of VAriance (ANOVA) statistical analysis.

In this article, a novel design of dielectric resonator antenna (DRA) with a reconfigurable radiation pattern capability is presented. Reconfigurability in the azimuth plane is achieved by symmetrically placing six electromagnetic bandgap (EBG) sectors around the DRA. Each sector is composed of 26 circular-shaped mushroom-like EBG unit cell. In order to achieve 360° pattern reconfigurability with a minimum number of diodes, a network of metallic veins printed on a conductor-backed dielectric slab is used to group and connect the vias in each EBG sector. In addition, a switching p-i-n diode is integrated to the circuit to control the beam steering in the entire azimuth plane toward the respective desired sector by turning on and off the diode. Sixty GHz DRA prototype incorporating the EBG switching circuit is fabricated and tested. Results show 360° pattern reconfigurability in the azimuth plane, with a realized gain of 4.2 dBi, and less than −16 dB impedance matching level over the desired bandwidth are achieved.

Publisher's version (útgefin grein), In this paper, a multiple-input-multiple-output (MIMO) antenna featuring circular polarization diversity, and designed on a common coplanar ground is presented. The proposed antenna design utilizes a coplanar waveguide (CPW) feeding technique with three parallel coplanar ground planes, and two feedlines in-between. For circular polarization (CP), quasi-loops are created by etching slots on the outermost ground planes. With this configuration, circular polarization diversity is induced in the MIMO antenna with the left-hand CP (LHCP) from one antenna and the right-hand CP (RHCP) from the other. The total footprint of the antenna radiator is only 0.78 lambda(0) x 0.55 lambda(0) = 0.42 lambda(2)(0). Experimental results show perfectly overlapping impedance and axial ratio bandwidths of 39.3% (4.5 GHz to 6.7 GHz). In addition, average in-band isolation vertical bar S-21 vertical bar, This work was supported in part by the Abu Dhabi Department of Education and Knowledge (ADEK) Award for Research Excellence, in 2019, under Grant AARE19-245, in part by The Icelandic Centre for Research (RANNIS) under Grant 206606051, and in part by the National Science Centre of Poland under Grant 2017/27/B/ST7/00563., "Peer Reviewed"

Publisher's version (útgefin grein), Uncertainty quantification is an important aspect of engineering design, also pertaining to the development and performance evaluation of antenna systems. Manufacturing tolerances as well as other types of uncertainties, related to material parameters (e.g., substrate permittivity) or operating conditions (e.g., bending) may affect the antenna characteristics. In the case of narrow- or multi-band antennas, this usually leads to frequency shifts of the operating bands. Quantifying these effects is imperative to adequately assess the design quality, either in terms of the statistical moments of the performance parameters or the yield. Reducing the antenna sensitivity to parameter deviations is even more essential when increasing the probability of the system satisfying the prescribed requirements is of concern. The prerequisite of such procedures is statistical analysis, normally carried out at the level of full-wave electromagnetic (EM) analysis. While necessary to ensure reliability, it entails considerable computational expenses, often prohibitive. Following the recently fostered concept of constrained modeling, this paper proposes a simple technique for rapid surrogate-assisted yield optimization of narrow- and multi-band antennas. The keystone of the approach is an appropriate definition of the optimization domain. This is realized by considering a few pre-optimized designs that represent the directions of the major changes of the antenna resonant frequencies and operating bands. Due to a small volume of such a domain, an accurate replacement model can be established therein using a small number of training samples, and employed to improve the antenna yield. Verification results obtained for a ring-slot antenna, a dual-band and a triple-band uniplanar dipoles indicate that the optimization process can be accomplished at low cost of a few dozen of EM simulations: 62, 74 and 132 EM simulations, respectively. Result reliability is validated through comparisons with EM-based Monte Carlo simulations., This work was supported in part by the Icelandic Centre for Research (RANNIS) under Grant 206606051, in part by the National Science Centre of Poland under Grant 2017/27/B/ST7/00563, and in part by the Abu-Dhabi Department of Education and Knowledge (ADEK) Award for Research Excellence, in 2019, under Grant AARE19-245., "Peer Reviewed"

This article presents a novel terahertz (THz) antenna array design comprising a layered structure of a perovskite material which enhances the radiation characteristics of an antenna overlaid on a conventional metallic antenna element. The simulated antenna consists of a THz gold patch antenna coated with a hybrid perovskite material, methyl-ammonium lead iodide CH3NH3PbI3 which enables the manipulation of the THz electromagnetic waves. In addition to this, we also present a comparison of the antenna properties of the proposed hybrid perovskite material with antennas made of gold and perovskite only. The proposed antenna operates in the frequency band 0.9 - 1.2 THz. The simulated impedance bandwidth of the proposed array antenna ranges from 0.9 THz to 1.2 THz with a reflection coefficient (S11) less than -10 dB. The antenna array has a radiation patterns stability on the whole frequency band. The peak gain obtained is 11.4 dBi with perovskite arrays. The hybrid and perovskite antenna array demonstrate high radiation efficiency. The designs presented here will help in realising future wireless communication systems that require miniaturisation, fast reconfigurability and wearability.

This paper presents a low-profile multiple-input multiple-output (MIMO) implantable antenna system including a capsule endoscopy and a scalp implantation at Medical Implant Communication Service (MICS) band (402–405 MHz), and Industrial, Scientific, and Medical (ISM) band (433.1–438.8 MHz). It consists of two elements with an edge-to-edge gap of 0.0018λg and overall dimensions of π × (5.65)2 × 0.13 mm3 and is placed on a 0.13 mm thick RO3010 (ϵr = 10.2, tanδ = 0.0022) substrate. The antenna is integrated with batteries, sensors, and electronic components in two different types of implantable devices (capsule and flat-type devices). The simulation result shows that the antenna has a fractional bandwidth (FBW) of 33.9%, a maximum realized gain of -30 dBi, and isolation of more than 26 dB. The fabricated prototype is measured in a saline solution and minced pork meat. The measured results are found in good accordance with simulations. The antenna parameters are calculated and showed a significant independence between the radiators. A link budget is estimated to be 78 Mb/s for a distance of 20 meters. Thus, the proposed antenna is considered as a promising solution for high data-rate medical applications such as capsule endoscopy, live surgeries, and other biomedical applications where the high data-rate is required.

Proposed in this paper is the design of an innovative and compact antenna array which based on four radiating elements for multi-input multi-output (MIMO) antenna applications used in 5G communication systems. The radiating elements are fractal curves excited using an open-circuited feedline through a coplanar waveguide (CPW). The feedline is electromagnetically coupled to the inside edge of the radiating element. The array's impedance bandwidth is enhanced by inserting a ground structure composed of low-high-low impedance between the radiating elements. The low-impedance section of the ground is a staircase structure that is inclined at an angle to follow the input feedline. This inter-radiating element essentially suppresses near-field radiation between adjacent radiators. A band reject filter based on a composite right/left hand (CRLH) structure is mounted at the back side of the antenna array to reduce mutual coupling between the antenna elements by choking surface wave propagations that can otherwise degrade the radiation performance of the array antenna. The CRLH structure is based on the Hilbert fractal geometry, and it was designed to act like a stop band filter over the desired frequency bands. The proposed antenna array was fabricated and tested. It covers the frequency bands in the range from 2 to 3 GHz, 3.4-3.9 GHz, and 4.4-5.2 GHz. The array has a maximum gain of 6. 2dBi at 3.8 GHz and coupling isolation better than 20 dB. The envelope correlation coefficient of the antenna array is within the acceptable limit. There is good agreement between the simulated and measured results. Dr. Mohammad Alibakhshikenari acknowledges support from the CONEX-Plus programme funded by Universidad Carlos III de Madrid and the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 801538. Funding for APC: Universidad Carlos III de Madrid (Read & Publish Agreement CRUE-CSIC 2022).

A novel millimeter-wave (MMW) hybrid isolator is presented to reduce the mutual-coupling (MC) between two closely-spaced dielectric resonators (DR) antennas at 60 GHz. The proposed hybrid isolator consists of a combination of a new uni-planar compact electromagnetic band-gap (EBG) structure and an MMW choke absorber. The design of the proposed EBG unit-cell is based on the stepped-impedance resonator (SIR) technique. The results show that the proposed EBG structure provides a wide frequency bandgap in the 60 GHz band with miniaturization factors of 0.79 and 0.66 compared to conventional uni-planar EBG and uni-planar compact (UC-EBG) structures, respectively. The proposed EBG is then placed between two Multiple-Input Multiple-Output (MIMO) DR antennas to reduce the MC level. As a result, an average of 7 dB level reduction is obtained. To further reduce the MC level, a thin MMW choke absorber wall is mounted vertically between the two DR antennas and above the EBG structure. An average of 22 dB MC reduction is achieved over the suggested bandwidth while maintaining good radiation characteristics. The measured isolation of the prototype antenna varies from -29 to -49 dB in the frequency range from 59.3 to 64.8 GHz. In fact, the proposed hybrid isolator outperforms other hybrid isolation techniques reported in the literature.

Statistical analysis is of practical importance for high-frequency engineering when it comes to estimating the effects of manufacturing tolerances and other types of uncertainties on system properties. One of its bottlenecks, in the case of antenna structures, is a high computational cost of full-wave electromagnetic (EM) analysis normally utilized for reliable performance evaluation. This paper capitalizes on the recently introduced concept of surrogate modeling in constrained domains and delivers a simple yet computationally-efficient procedure for statistical analysis and yield optimization of multi-band antennas. The foundation of our methodology is an appropriate definition of the parameter space region selected for a construction of the fast surrogate model replacing EM analysis for the purpose of Monte Carlo simulations. The metamodel domain is spanned by the vectors corresponding to the most significant changes of antenna resonant frequencies. It is characterized by a small volume (as compared to the traditional interval-like domain), which translates to reduced expenses of training data acquisition, and, consequently, the overall cost of the yield optimization process. Our approach is validated using a triple-band dipole antenna with the yield-optimum design identified at the cost of only a few dozens of EM simulations of the antenna structure.

High cost of electromagnetic (EM)-simulation-based antenna design fosters the incorporation of surrogate modeling techniques as the most promising tools for expediting the procedures such as parametric optimization or uncertainty quantification. Data-driven metamodels are by far the most popular ones due to their versatility and easy handling even by inexperienced users. Notwithstanding, construction of reliable surrogates for contemporary antenna structures is, in a large part, hindered by the curse of dimensionality and nonlinear relationships between the geometry parameters and antenna characteristics. A possible workaround are performance-driven modeling methods. The idea it to restrict the construction of the surrogate to small parts of the parameter space, containing designs that are of high quality with respect to the relevant figures of interest. This leads to a significant reduction of the required number of training samples, the improvement of the model predictive power, and a possibility of representing antenna outputs over broad ranges of operating conditions. The model domain is established using the sets of so-called reference designs that need to be pre-optimized beforehand. The CPU cost of this acquisition adds to the overall expenses of surrogate model setup and may undermine the computational benefits of the performance-driven modeling paradigm. This paper proposes an alternative approach, where gradient-enhanced kriging is employed to reduce the number of required reference points, thus leading to lowering the cost of the model setup without compromising its accuracy. A quasi-Yagi antenna example is provided for demonstration purposes.