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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.

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.

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.

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.

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.

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.

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.

Radiator correlation in multiple-input-multiple-output (MIMO) antenna has always been a serious concern for MIMO systems. In this paper, an antenna consisting of two parallel-placed coplanar waveguide (CPW)-fed radiators engineered on a common coplanar ground plane is presented. The antenna is designed with three parallel coplanar ground planes and two feed lines. The two outermost ground planes are systematically modified by etching a slot to form a quasi-loop, whereas the middle ground plane is made asymmetric along the feeding line. The current flowing on the edges of the quasi-loops generates opposite senses of circular polarization due to switched positioning of the slotted ground plane with respect to the feedline. This induces polarization diversity in the antenna. The proposed structure with circular polarization diversity features a low level of envelop correlation coefficient (ECC), $\vert \mathrm{S}_{11}\vert \leq-10\ \text{dB}$ ) and axial ratio (AR) bandwidth of approximately 38.5% from 4.7 GHz to 6.7 GHz. The average in-band isolation is ( $\vert \mathrm{S}_{21}\vert \leq-15\ \text{dB}$ ) with the peak realized gain of 3.15 dBic when operated with the bi-directional radiation characteristics in the $\pm z$ -direction.

To achieve 1 Tb/s wireless links considering simplified modulation schemes, that are in short-range and at terahertz (THz) frequencies, the quest for overwhelming extreme bandwidths is self-evident. In this paper, we analyze the channel performance and limitations of THz communication systems at 300 GHz carrier frequency due to the horn-antenna beam misalignment in line-of-sight (LoS) scenario. Firstly, a ray-tracer is employed to examine the implications of beam spot size for varied distances. Then, these effects are studied in terms of link coverage and the achievable data rates when altering the antenna positions horizontally and vertically. A VNA-based 300 GHz transmission system is used to experimentally validate the above mentioned implications in terms of distance and antenna positions. Finally, the impact of beam spot size is studied by rotating the antennas. To the best of our knowledge, this work reports the first ever recorded implications of beam spot size on the THz wireless links.

Printed ridge gap waveguide (PRGW) is considered among the state of art guiding technologies due to its low signal distortion and low loss at Millimeter Wave (mmWave) spectrum, which motivates the research community to use this guiding structure as a host technology for various passive microwave and mmWave components. One of the most important passive components used in antenna beam-switching networks is the quadrature hybrid directional coupler providing signal power division with 90° phase shift. A featured design of a broadband and compact PRGW hybrid coupler is propose in this paper. A novel design methodology, based on mode analysis, is introduced to design the objective coupler. The proposed design is suitable for mmWave applications with small electrical dimensions ( $1.2\,\,\lambda _{o} \times 1.2\,\,\lambda _{o}$ ), low loss, and wide bandwidth. The proposed hybrid coupler is fabricated on Roger/RT 6002 substrate material of thickness 0.762 mm. The measured results highlight that the coupler can provide a good return loss with a bandwidth of 26.5% at 30 GHz and isolation beyond 15 dB. The measured phase difference between the coupler output ports is equal $90^\circ \pm ~5^\circ $ through the interested operating bandwidth. A clear agreement between the simulated and the measured results over the assigned operating bandwidth has been illustrated.

A simple-topology circularly polarized (CP) multiple-input-multiple-output (MIMO) antenna with polarization diversity is presented. The proposed design comprises two parallel placed coplanar waveguide (CPW)-fed antennas with the opposite senses of polarization. Circular polarization is induced in the antenna by simple geometrical modification of the conducting coplanar ground planes on the right/left side of the microstrip transmission line. To achieve polarization diversity, the left-hand and right-hand CP is realized by simply switching the positions of the ground plane with respect to the microstrip line monopole. Owing to this configuration, the proposed antenna features a wide impedance bandwidth $(\vert \mathbf{S11}\vert\leqslant-\mathbf{10\ dB})$ and axial ratio (AR) bandwidth from 5.2 GHz to 6.3 GHz along with high isolation of $\vert \mathbf{S21}\vert\leqslant-\mathbf{20\ dB}$ in the entire operating frequency range. The peak realized gain of the antenna is 5.8 dBic, the envelope correlation coefficient (ECC) is less than 0.004 with the maximum diversity gain (DG) of approximately 9.99 dB.

Publisher's version (útgefin grein), Over the recent years, surrogate modeling has been playing an increasing role in the design of antenna structures. The main incentive is to mitigate the issues related to high cost of electromagnetic (EM)-based procedures. Among the various techniques, approximation surrogates are the most popular ones due to their flexibility and easy access. Notwithstanding, data-driven modeling of antenna characteristics is associated with serious practical issues, the primary one being the curse of dimensionality, particularly troublesome due to typically high nonlinearity of antenna responses. This limits applicability of conventional surrogates to simple structures described by a few parameters within narrow ranges thereof, which is grossly insufficient from the point of view of design utility. Many of these issues can be alleviated by the recently proposed constrained modeling techniques that restrict the surrogate domain to regions containing high-quality designs with respect to the relevant performance figures, which are identified using the pre-optimized reference designs at an extra computational effort. This paper proposes a methodology based on gradient-enhanced kriging (GEK). It enables a considerable reduction of the number of reference points required to construct the inverse surrogate (employed in surrogate model definition) by incorporating the sensitivity data into the nested kriging framework. Using two antenna examples, it is demonstrated to yield significant savings in terms of the surrogate model setup cost as compared to both conventional modeling methods and the original nested kriging., 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"

In this paper, A miniaturized dual-band implantable antenna using meandered line resonator is proposed for bio-telemetry applications. The proposed antenna has dual-band (0.91 GHz and 2.45 GHz) operation, covering the important Industrial, Scientific and Medical (ISM) bands. Miniaturization is achieved using meandered resonator and a square slot etched in the ground plane. The performance of the proposed antenna inside a quasi-implantable biomedical device (IBD) is analysed in a homogeneous skin model, human intestine and human head. The measurements are performed by implanting the quasi-IBD inside a saline solution and minced pork meat. The quasi-IBD consists of the proposed antenna, batteries and printed circuit board (PCB) with electronic components on it. The proposed antenna has compact dimensions of 5.6 × 5 . 8 × 0.25 mm3. The measured peak gains in the minced pork meat are −22.9 dBi and −22.1 dBi at 0.91 GHz and 2.45 GHz, respectively. The low specific absorption rate (SAR) of the proposed antenna allows maximum input power of 3.32 mW at 0.91 GHz and 4.37 mW at 2.45 GHz. To the best of the authors’ knowledge, this is the most compact dual-band implantable antenna reported in the literature for 0.91 GHz and 2.45 GHz ISM bands.

A new millimeter-wave (MMW), electromagnetic band-gap (EBG) structure is presented. The proposed EBG structure without the use of metallic vias or vertical components is formed by etching two slots and adding two connecting bridges to a conventional uniplanar EBG unit-cell. The transmission characteristics of the proposed EBG structure are measured. Results show that the proposed EBG structure has a wide bandgap around the 60 GHz band. The size of the proposed EBG unit-cell is 78% less than a conventional uniplanar EBG, and 72% less than a uniplanar-compact EBG (UC-EBG) operating at the same frequency band. Moreover, and despite the fabrication limitations at the 60 GHz band, the proposed EBG unit-cell provides at least 12% more size reduction than any other planar EBG structures at microwave frequencies. Its enhanced performance and applicability to reduce mutual coupling in antenna arrays are then investigated. Results show a drastic decrease in the mutual coupling level. This EBG structure can find its applications in MMW wireless communication systems.

A new millimeter-wave (MMW), frequency-selective surface (FSS) unit-cell is presented. The reflection and transmission characteristics of the proposed FSS structure are investigated. Results show that by using only one PIN diode in each unit-cell, the transmissive/reflective bands can be altered. The proposed FSS is then incorporated as in MMW aperture-coupled dielectric resonator (DR) antenna to achieve beam steering and pattern diversity. By sequentially biasing the diodes, beam steering can be achieved along the entire azimuth plane. Moreover, by configuring the states of the diodes, directional and Omni-like patterns can be obtained.

Millimeter-wave (MMW) electromagnetic bandgap (EBG)-based dielectric resonator (DR) antenna with beam steering capability is presented. Six EBG sectors of several cells are placed symmetrically around the DR antenna to achieve beam steering in the azimuth plane. Each sector is composed of twenty one circular-patch mushroom EBG unit cell. The vias in each sector are connected through thin metallic veins printed on a conductor-backed dielectric slab. The metallic veins are then connected to the ground plane through a switching diode. By switching the diode on and off, the EBG sector band-stop and band-pass properties are changed, yielding beam steering into that sector. Results show flexible and effective beam steering capability in the azimuth plane using minimal number of diodes.

In this paper, a millimeter-wave aperture-coupled dielectric resonator antenna (ACDRA) with low back radiation is presented. Back radiation reduction was achieved through a circular patches-mushroom like EBG structure placed underneath the antenna. Simulated results show 18 dB improvements in the backward radiation compared to the case where no EBG is used.

The use of dielectric resonator antennas (DRAs) is motivated by their low loss, small size, and their ability to produce unidirectional radiation patterns with small back side radiation. Previously, researchers used one DRA to produce dual band performance when excited by a slot radiator. Consequently, unidirectional patterns are achieved only in one band, which corresponds to the DRA resonance. However, in this paper, two DRAs are fed simultaneously by a coplanar waveguide (CPW) through two slots in the CPW ground plane. Here, the DRAs, not the slots, act as radiators and therefore unidirectional radiation is achieved at both bands. Using the commercial softwares HFSS and CST, the dimensions of the dual antenna are tuned such that the antenna radiates at 4.5 and 6.5 GHz with very good agreement between the two softwares. A full parametric study is carried out.

The use of dielectric resonator antennas (DRAs) is motivated by their low loss, small size, and their ability to produce unidirectional radiation patterns with small back side radiation. Previously, researchers used one DRA to produce dual-band performance when excited by a slot radiator. Consequently, unidirectional patterns are achieved only in one band which corresponds to the DRA resonance. However, in this paper, two DRAs are fed simultaneously by a coplanar waveguide (CPW ) through two slots in the CPW ground plane. Here, the DRAs, not the slots, act as radiators and therefore unidirectional radiation is achieved at both bands. Using the commercial softwares, HFSS and CST, the dimensions of the dual antenna are tuned such that the antenna radiates at 4.5 and 6.5 GHz with very good agreement between the two softwares. A full parametric study is carried out.

Dual band antennas are important in communication systems which operate in more than one frequency band. This paper presents a new dual band coplanar waveguide- fed- slot coupled rectangular dielectric resonator antenna operating at the two frequency bands centered at 5.4 and 6.8 GHz. The use of DR allows for unidirectional radiation with a front to back ratio of more than 10 dB. The designed antenna is linearly polarized with a cross polarization level more than 26 dB lower than the co-polarization level.