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Here, we propose a low-profile polarizing technique integrated in a parallel plate waveguide (PPW) configuration, compatible with fully metallic geodesic lens antennas. The geodesic shape of the antenna is chosen to resemble the operation of a Luneburg lens. The lens is fed with 11 waveguide ports with 10° separation producing 11 switchable beams in an angular range of $\pm \mathrm{50}^{\circ }$. Two metallic polarizing screens are loaded into the aperture of the antenna to rotate the electric field from a vertical linear polarization, which is the polarization of the transverse electromagnetic (TEM) mode supported in the lens, to a $+ \mathrm{45}^{\circ }$ linear polarization. Since the polarizing unit cells are integrated into the aperture of the antenna, the final design is compact. In addition, the size of the polarizing unit cells is about $0.55\lambda $ at the central frequency of operation making the antenna suitable to produce an array formed of stacked lenses. A prototype of the antenna in the $\text{K}_{\text {a}}$ -band was manufactured and tested, verifying the performance obtained in simulations. [ABSTRACT FROM AUTHOR]

A triangular monopole antenna and a bitriangular slot antenna are designed and measured, respectively, in order to validate a relation between the input impedances of such noncomplementary antennas. The first application of the newly validated impedance relation is demonstrated with the creation of nonself-complementary antennas, which consist of the triangular monopole and the bitriangular slot. As expected, the nonself-complementary antennas indeed exhibit broad impedance bandwidths and stable radiation patterns. Furthermore, the novel nonself-complementary antennas have the advantages of simpler structures and feed than those of the existing nonself-complementary antennas. Hence, they can be easily and inexpensively manufactured. [ABSTRACT FROM AUTHOR]

A novel method of synthesizing shaped-beam cylindrical conformal array by rotating the antenna elements and optimizing their excitation phases is presented. Rotation of antennas on curved surface is mathematically described by rotating its vectorial active element pattern (VAEP) in its local coordinate system (LCS). Then the scalar patterns and polarization unit vectors of all the rotated VAEPs are properly transformed and then interpolated at a unified angle sampling grid in a common coordinate system, where they are summed to obtain an approximated array expression. With this expression, element rotations and phases can be optimized using the constriction factor particle swarm optimization (CF-PSO) to synthesize desired shaped-beam pattern with controlled sidelobe level (SLL) and cross-polarization level (XPL). However, since rotations on curved surface introduce considerable variations to the element curvature and mutual coupling (MC), the synthesized array pattern would have considerable errors. A refined strategy is adopted then to improve the synthesis accuracy. The proposed method uses uniform amplitude weighting, thus saving many unequal power dividers. Three typical shaped pattern synthesis examples are provided to show the effectiveness of the proposed method. A cylindrical array prototype with 24 rotated U-slot loaded patch antennas is fabricated and measured for practical validation. [ABSTRACT FROM AUTHOR]

This article presents a millimeter-wave (mmWave) dual-band dual-polarized filtenna, which can achieve desirable out-of-band rejection for 5G applications. The dual-band dual-polarized antenna element consists of two fully-shielded quarter-mode substrate integrated waveguide (FSD-QMSIW) cavities and a dual-band stacked ring antenna. Two parts are coupled through the slot on the ground. The cavities are completely enclosed by the metal holes and copper cover to eliminate radiation loss. The loaded slots can tune the frequencies of the first two modes in the FSD-QMSIW cavity for dual-band operation. The inherent transmission null between the dual modes is generated to improve the stopband attenuation. To verify the proposed method, a dual-band dual-polarized filtenna with a three-order filtering function and four radiation nulls is designed and fabricated. The −10 dB impedance bandwidth can effectively cover 5G n258 (24.25–27.5 GHz) and n260 (37–40 GHz) bands in the measurement. The gains of two polarizations drop over 20 dB between the two bands. A four-element filtenna array is constructed to test its beam-scanning ability and further integrated with active beamformer integrated circuits (ICs). The measured results show that the fabricated filtenna array maintains satisfactory out-of-band rejection performance and can be one of the most promising 5G communication candidates. [ABSTRACT FROM AUTHOR]

A low-profile and wideband unidirectional antenna with ferrite loading is presented for ultrahigh-frequency (UHF) applications. This design comprises a slotted bowtie antenna with parasitic elements placed 50 mm over a ground plane. A small amount of ferrite loaded on the center of the ground plane plays a crucial role in improving the performance of the low-profile antenna. The ferrite used here is a new type of magnetodielectric material with relatively high permeability and permittivity, as well as low magnetic and dielectric loss. The loaded ferrite introduces an additional phase change of the electromagnetic field reflected by the ground to improve the impedance matching, bandwidth, efficiency, and gain of the low-profile antenna. The evolution process and mechanism of the proposed antenna are elaborated. For validation, an optimized antenna prototype was fabricated and measured. The measured results are consistent well with their simulations, which shows the realized gain of 7.2–9 dBi over $\vert \text{S}_{11}\vert \le -10$ dB impedance bandwidth of 38% (480–705 MHz). The overall profile of this antenna is only $0.08\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the lowest frequency of operation. [ABSTRACT FROM AUTHOR]

In this article, a four-antenna module in a capsule endoscopy is proposed for multiple-input multiple-output (MIMO) operation to achieve the purpose of real-time transmission of high-resolution images with high data rates. For compactness, the proposed design adopts conformal architecture and fully utilizes the inner wall space of the capsule body to accommodate four antennas in the very limited space of the capsule endoscope. For the availability of MIMO operation, three different technical approaches are used to decouple or improve the isolation between neighboring antenna elements and between diagonal antenna elements. System considerations (interaction between the electronic components and the antenna in the endoscope) and specific absorption ratio (SAR) evaluation are performed to verify the robustness and human safety of the proposed design, respectively. In addition, link margin analysis and MIMO channel parameter studies are carried out to verify the wireless telemetry performance and MIMO operation performance, respectively. Antenna prototypes were fabricated and implanted in minced pork for ex-vivo measurements (S-parameters, gain, and radiation patterns). The measured overlapping impedance bandwidth of the four antenna elements is 120 MHz, which can fully cover the 915 MHz industrial scientific medical (ISM) band. The measured isolation between the neighboring antenna elements and the diagonal antenna elements is better than 20 and 10 dB, respectively. The measured maximum peak realized gain is −18.1 dBi. [ABSTRACT FROM AUTHOR]

A novel bandwidth enhancement method using loading multiple parasitic structures to realize broadband miniaturized antenna is proposed. Based on the proposed strategies, one miniaturized wideband dual-polarized dipole antenna covering LTE/CDMA/GSM bands (690–960 MHz) for base-station application is designed. The antenna consists of two folded bowtie-shaped dipoles fed with a pair of crossed baluns, and is further loaded on a ceramic block with high permittivity ($\varepsilon$) for miniaturization. A parasitical square loop is loaded for bandwidth enhancement at a lower frequency. In addition, four split rings with a small square loop are firstly adopted for antenna resonance tuning, the impedance bandwidth is thus improved effectively. The antenna size is only $0.18\,\times \,0.18\,\times \, 0.22\,\,\lambda _{0}$ at the center frequency. The measured result of the fabricated prototype exhibits a relatively large operation bandwidth of 32.73% (VSWR < 1.6) with stable radiation patterns and relatively flat broadside gains. Moreover, to verify the feasibility of the proposed miniaturized antenna element in the base-station application, an array of $2\,\times \, 4$ is further designed. The measured results of the array indicate isolation over 20 dB with an impedance bandwidth of 32%. Due to the good performance and compact feature, the proposed miniaturized broadband antenna element can find large application potential in multiband wireless communication base stations. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) is a widely used wireless technology for contactless data exchange between a passive information carrier (tag) and an active interrogation device (reader). Being sensitive to a surrounding environment, RFID tags are usually designed per application. Here, we demonstrate an RFID tag with three essential functions available simultaneously, namely, small footprint, long reading range, and capability of on-metal labeling. Our design is based on a compact high-index ceramic resonator and an inductively coupled small metal ring functionalized with an RFID chip. The tag operates at magnetic dipolar resonance, which interacts with the metal object subject to labeling. Specifically, a 16.5 mm $\times16.5$ mm $\times12$ mm footprint device, placed on a 40 cm $\times40$ cm metal sheet, was successfully interrogated from 22 m with no violation of international effective isotropic radiated power (EIRP) standards. Currently, it is the smallest on-metal RFID tag with a reading range of over 20 m. Multifunctional miniature long-range ceramic tags are attractive for use in numerous practical applications, including the Internet of Small Things (IoST) and many others. [ABSTRACT FROM AUTHOR]

This article introduces a novel near-field focus (NFF) lens antenna with a three-dimensional (3-D) focus-steering capability operating at terahertz (THz) frequencies. The antenna consists of a pair of thin discrete dielectric lenses (DDLs) placed above a stationary feed horn. First, we demonstrate that the DDL doublet’s in- plane synchronous counter-rotation and co- rotation could scan its focus radially and azimuthally, respectively. A multi-focus synthesis method that compensates the required transmission phases at multi-focus points is developed to further improve its NFF-steering performance. The DDL-based antenna can realize 3-D focus-scanning using a combination of rotation and linear translation mechanisms. The 3-D printing is adopted to fabricate the THz antenna to simplify the manufacturing process and reduce the cost. Both numerical and experimental results demonstrate that the 15 mm-diameter antenna prototype can scan its focus in a 3-D cylindrical space with a diameter of 29 mm and a length of 8 mm at 300 GHz. The proposed 3-D focus-scanning antenna with a large field of view (FoV) of 72° will open new avenues for fast 3-D THz imaging applications. [ABSTRACT FROM AUTHOR]

This work introduces cost-effective solution for a millimeter-wave (mmW) antenna array development. We suggest an elliptical cavity-backed patch antenna array to achieve a wideband and high-gain circularly polarized (CP) at mmW frequencies. The whole array only uses two PCBs and a metallic fixture to build. We introduce a new configurable subarray with $2\times $ 1 radiating elements that are formed by two partially overlapped elliptical cavities to generate the radiation together with the driven patches of the subarray. The subarray can produce a wide impedance bandwidth of 37%, a wide 3 dB axial ratio (AR) bandwidth of 29.6%, and a maximum gain of 11.6 dBic. Based on the result from the subarray, we design a 32-element antenna array by a $4 \times $ 4 antenna array configuration. The power distribution is realized by a 1-to-16 full-corporate feed network. The measured results show that the proposed CP array obtains an impedance bandwidth of 31.5% and a 3 dB AR bandwidth of 24%. In addition, the gain of the array is from 19.1 to 21 dBic within the 3 dB AR bandwidth. With wide impedance and AR bandwidths, the proposed antenna array can find potential applications in long-range mmW communications. [ABSTRACT FROM AUTHOR]

The identification of unknown antennas and analysis of electromagnetic wave vulnerability are important for effective attacks and/or protection in high-power electromagnetics (HPEM). Using electromagnetic clues, antenna modeling becomes possible, and its electromagnetic properties can be analyzed by predicting area-wide radiation patterns. To model an antenna, an infinitesimal dipole modeling (IDM) technique, utilizing clues from sparse far-field patterns, was used in the present study. The IDM approach obtained the equivalent infinitesimal dipole (ID) for the antenna configuration current using Green’s function. The sparse far-field pattern was determined for a movement trajectory, using air reconnaissance. Random far-field data acquisition paths were considered cumulatively in the 1–10 range in this case. The approach also used external exposure information about the antenna, such as the operating frequency and size. For simulations and measurements, a ridged-horn antenna operating at 2.4 GHz was used. The overall radiation pattern reconstructed using the IDM approach was correlated at 0.78 when one path was considered in the simulations. As the considered paths were accumulated, the correlation tended to increase, with the correlation for ten paths exceeding 0.98. The estimated radiation pattern characteristics of antennas can be utilized for communication reception characteristics and/or electromagnetic wave vulnerability analysis. [ABSTRACT FROM AUTHOR]

Coupling of multiphysics including electrodynamics, elastodynamics, magnetodynamics, and electromagnetic (EM) radiation is involved in the operating process of bulk acoustic wave (BAW) antenna. There is still no good way to design the structure and evaluate the performance of the antenna in theory. Therefore, the multiphysics dynamic coupling model of the antenna is constructed by uniting Newton’s equation for acoustic wave, Maxwell’s equation for EM wave, and Landau–Lifshitz–Gilbert (LLG) equation for spin wave with constitutive relations of multiferroic materials to discuss the dispersion law of permeability and magnetomechanical coupling factor for the magnetostrictive layer. The importance of consistency between ferromagnetic resonance (FMR) frequency and BAW resonant frequency is demonstrated. The analysis shows that both increasing the anisotropic field or the saturation magnetization and decreasing the FMR linewidth are beneficial to improving the internal energy conversion efficiency and the average radiated power for BAW antenna. In addition, a micromagnetic module is introduced into finite element analysis (FEA) software to simulate the precession of unit magnetic moment at different frequencies. Thus, the analytical model is verified from the perspective of power absorption. [ABSTRACT FROM AUTHOR]

This communication investigates design requirements for a class of dual-polarized in-band full-duplex (IBFD) antennas utilizing a symmetry of structures and a differential-feeding scheme. The analysis reveals that, to achieve zero coupling between two ports, the out-of-phase power divider (PD) does not need to have perfect isolation and perfect matching at the two output ports. A more relaxed set of requirements for the PD is derived for the first time. Based on this, an ultra-wideband cross-shaped Vivaldi antenna is designed for IBFD applications with very high isolation. The measured 10 dB return loss bandwidth is 1.26–8.0 GHz (145.5%), while the measured port-to-port isolation is >42 dB at 1.26–4.7 GHz (115.4%) and >34 dB within the whole operational bandwidth. [ABSTRACT FROM AUTHOR]

A cylindrical antenna with a conductively loaded slot (CACLS) is designed for broadband imaging radar applications. Through design considerations, such as conductive loading, cylinder termination, and the insertion of an electromagnetic (EM) wave absorber into the cylinder, the proposed CACLS is shown to be able to radiate temporally short and nondispersive pulses. Based on the final design of the antenna, parametric studies pertaining to the time-domain radiation performances depending on the dimension of the cylinder are performed. The CACLS with the determined design parameters is then fabricated and its performances verified through antenna measurements and a radar experiment. In addition to its excellent pulse radiation and reception performance, the realized antenna has a compact and physically robust structure, which makes it potentially suitable for many broadband imaging radar applications. [ABSTRACT FROM AUTHOR]

High-performance miniaturized antennas are one of the goals that have been pursued in the design of wireless communication systems for implantable medical devices. In this article, a 915 MHz novel-shape loop antenna conforming to the inner wall of the capsule is developed by comprehensively adopting meander and symmetrical structure patch, folding technique, and vector current reversal technique. Through electromagnetic simulation, testing, and experimentation, the antenna shows good characteristics such as small size, ultra-wideband, circular polarization, strong robustness, and safety. Specific performances include the following: 1) the size of the developed miniaturized loop conformal antenna is only 30.5 mm $\times $ 4.6 mm $\times $ 0.05 mm and the maximum gain is −21.5 dBi at 915 MHz, which solves the problem of low gain due to the small antenna radiation area; 2) the antenna has a 4.5 GHz ultra-wideband impedance matching bandwidth ($\vert S_{11}\vert < -10$ dB) from 0.5 to 5 GHz. Even if the parameters such as the implantation depth and the thickness of the capsule shell change, or there exists a wireless power transfer system, the antenna can still cover the required frequency band with strong robustness; and 3) the specific absorption rate (SAR) of human tissues radiated by the antenna is far lower than the safety limit in IEEE standards and ICNIRP guidelines. The experimental platform using pork to simulate human tissues was built for antenna performance testing and communication testing. The measurement results verified the good resonance performance, radiation characteristics, and omnidirectionality of the developed antenna. The antenna link loss model is also given, which has been used in wireless communication and localization. [ABSTRACT FROM AUTHOR]

A new method for frequency selective surface (FSS) with high selectivity, namely, filtenna–filtenna (FA-FA)-based technique, is proposed, which consists of two filtering antennas and impedance matching network. Based on the reciprocity theorem, the radiation null of filtenna can provide a stopband of the proposed FSS. In this work, it is validated by using a periodic array of back-to-back magnetoelectronic (ME)-dipole antennas with split-ring resonators (SRRs), and a slotted GND plane is used to connect the two ME-dipole antennas for impedance matching. Bandpass response of the proposed FSS is realized by the intrinsic high-pass characteristic of ME-dipole antennas and the bandstop characteristic of SRRs. Four transmission zeros (TZs) and three transmission poles (TPs) are generated, exhibiting a high-order filtering response. TZs and TPs are analyzed by equivalent circuit model and current distributions. The 3 dB fractional bandwidth (${\mathrm {FBW}}_{\mathrm {3\,dB}}$) of 38.5% in the passband and the 20 dB fractional bandwidths $({\mathrm {FBW}}_{\mathrm {20\,dB}})$ of 8.7% in the lower rejection band and 13.8% in upper rejection band are obtained in this design. Finally, a prototype is fabricated and measured to further validate the proposed FA-FA-based technique. Simulated and measured results show that the proposed FA-FA-based FSS is with the distinct advantages, including wide passband, low profile, tunable TZs, and dual-polarized application, which verifies the proposed method of FSSs. [ABSTRACT FROM AUTHOR]

This communication presents the design and implementation of a beam steerable leaky wave antenna (LWA) based on integrated electronic devices (varactor diodes). The design uses a half-mode substrate-integrated waveguide (HMSIW) where the short-circuited wall or PEC boundary is realized with field programmable microwave substrate (FPMS)-based unit cells. By virtue of placing integrated varactor diodes in these unit cells, the wavenumber and the phase shift of the propagating signal can be controlled. This allows a beam steering of 25° for a fixed center frequency. Furthermore, control of the varactor bias voltages allows a fixed beam direction over a wide frequency bandwidth. An excellent agreement can be observed between the simulated and measured results, validating the first ever FPMS-based reconfigurable antenna design. [ABSTRACT FROM AUTHOR]

This article presents a planar switching integrated quadrant coil antenna to mitigate lateral and angular misalignment problems in near-field wireless power transfer (WPT) applications. To allow a completely free receiver movement, both the misalignment problems are concurrently addressed by forming widespread distributions of switched polarized H-field in the receiver region. To achieve this, current circulations through the four quadrant coils composing the proposed antenna are judiciously controlled to form three orthogonal H-field components. For lateral misalignment mitigation, the widespread field distributions are obtained by using a field-forming approach for optimizing the antenna parameters. To produce the switched polarized H-field for angular misalignment mitigation, time-switching of the orthogonal H-field components is performed. This switching operation is realized by three double pole double throw (DPDT) switches interconnecting the coils and integrated within the design for a cost-effective planar antenna solution. The fabricated prototype is measured and the experimental results are corroborated with the analysis. The results demonstrate the potential of the proposed antenna to simultaneously mitigate both the misalignment problems for medium-range WPT of small devices, such as medical implants, wireless endoscopy capsules, and wearable devices, which are allowed to freely rotate and displace. [ABSTRACT FROM AUTHOR]

The motion of a very-low-frequency (VLF: 3–30 kHz) orbiting antenna across the Earth’s magnetic field will generate the Lorentz force, which not only compromises the efficiency of the antenna, but also causes it to fall out of orbit over a long time. This article investigates the Lorentz force and dissipated power of a VLF space-borne linear antenna in an anisotropic magnetoplasma as well as the deorbiting time of the system. By considering the inhomogeneity of the current and the effect of ordinary and extraordinary waves, we systematically quantified and analyzed the Lorentz force on the antenna in an anisotropic scenario. The dissipated power and system deorbiting time are then determined by integrating antenna theory and electrodynamics. The results show that the Lorentz force and the power will increase with the antenna length and radius, whereas the deorbiting time will decrease accordingly. It is also found that as the geomagnetic inclination angle increases, the Lorentz force and the power will slightly decrease. The proposed method can estimate the Lorentz force, power, and deorbiting time for arbitrary antennas, low Earth orbital conditions, and VLF ionospheric parameters. This work may also help eliminate the adverse effect and evaluate the deorbiting performance of the VLF space-borne system from an analytical perspective. [ABSTRACT FROM AUTHOR]

The foremost method to exhaust heat sourced from electronic devices is to use heat sinks. However, in practice, these structures behave as actual antennas and cause interference problems. The selected heat sink like many others is performing like a real antenna whose gain at 4.9 GHz is ~ 7 dBi both in simulation and measurement. In this study, a novel gain (radiation pattern) controlling belt made up of a metamaterial (MTM) structure was designed and dressed to the heat-sink antenna. The effect of the position of the belt on the antenna pattern is investigated. The sliding position of the belt which allows for dynamic gain control varies the antenna gain between 3.38 and 7.36 dBi (~ 7 dB in ${\theta }$ angle and ~ 9 dB in ${\emptyset }$ angle). Maximum gain enhancement reaches up to 18.43 dB and maximum suppression ratio reaches up to 21.36 dB for the entire angle. [ABSTRACT FROM AUTHOR]

A compact wide-beam endfire antenna with ground radiation mode and vertically polarized mode for circular polarization (CP) is presented in this article. The antenna is constructed based on a configuration of coupled-mode patch antenna (CMPA), which consists of two coupling cavities with a shorting wall, and can generate vertically polarized modes. The CP is realized through a pair of orthogonally polarized modes of horizontal and vertical polarizations. Meanwhile, rendering them acquires an equal amplitude and a 90° phase difference. The horizontally polarized radiation mode is realized through inserting a crossed ground slot. Offset probe feed is used to excite all the radiation modes and introduce an additional phase shift for the CP. A set of offset ground slots (OGSs) are then applied to perturb the electromagnetic coupling of the modes and adjust the phase and magnitude of the radiating electric fields (E-fields). Several effects are synthesized, which results in a wide-beam circularly polarized (CP) endfire radiation. Aiming to improve the radiation performances, a cavity-backed planar reflector was applied in the experiment. Simulated and measured results are detailed and analyzed, which demonstrate that the measured 3 dB axial ratio (AR < 3 dB) bandwidth (ARBW) ranges from 3.385 to 3.428 GHz (1.2%), and the peak gain can be up to 3.4 dBi if the planar reflector is added. The measured half-power beamwidth (HPBW) and 3 dB ARBW can be up to 88°/114° and 53°/112° at 3.4 GHz, respectively. The antenna size (excluding the reflector) is maintained at $0.49\lambda _{0}\times 0.25\lambda _{0}\times 0.017\lambda _{0}$ , where $\lambda _{0}$ is the wavelength in free space, performing a compact configuration. [ABSTRACT FROM AUTHOR]

Radiation efficiency is one of the key parameters for smartphone antennas. However, the actual mechanism governing radiation efficiency remains unclear, and a few works have been published. This work is an attempt to extend the theory of characteristic modes (TCMs) to the lossy smartphone antenna for gaining insight into what causes efficiency variation and realizing efficiency improvement. Compared with the classical TCM, the CM analysis (CMA) adopted in this work has the capacity to handle lossy smartphone antenna. By using such an analysis approach, we find, quite interestingly, that suppressing the higher-order modes is an effective optimization strategy to enhance efficiency. Then, an optimized antenna with considerable improvement in efficiency is proposed. Finally, to meet the requirement of practical application, the additional LC circuit and through holes are introduced into this proposed optimized antenna. GSM 900 of 890–960MHz can be covered by this finally proposed antenna, and the measured peak total efficiency is improved from 26% to 43%. Due to the attractive features of small heights (4 mm) and tiny clearances (0.25 mm), the proposed designs are promising for application in a smartphone with a full-view display and thin profile. [ABSTRACT FROM AUTHOR]

This communication proposes a novel dual-band shared-aperture antenna hybridizing Fabry–Perot cavity antenna (FPCA) and folded reflectarray (FRA), which operates at both sub-6 GHz and millimeter-wave bands with a large frequency ratio of 1:4.6. This antenna is composed of two substrates, with metasurface printed on the upper substrate and reflector layer printed on the lower one. The metasurface works as partially reflective surface (PRS) of FPCA at the sub-6 GHz band while acts as polarization grid of FRA at the millimeter-waveband. Thus, the FPCA and the FRA are able to share the same aperture with high aperture reuse efficiency. A composite feed structure combining waveguide with microstrip patch antenna is used to feed at two bands, implementing shared-aperture feed. This antenna achieves high gains at two bands without complicated feeding networks. A prototype operating at 5.4 and 25 GHz bands is designed, fabricated, and measured to verify the idea. [ABSTRACT FROM AUTHOR]

In this article, a wideband shared-aperture phased array antenna is proposed for synthetic aperture radar (SAR) applications. A metal cavity-backed slot antenna and a slot antenna are used as the L- and X-band antenna elements, respectively. Notably, the X-band antenna elements are mounted on top of the L-band ones, and their interactions are successfully isolated by loading a layer of frequency selective surface (FSS). The FSS layer reflects the electromagnetic waves in X-band and allows transmission of the L-band electromagnetic waves, making the shared-aperture antenna work properly in L- and X-bands. Furthermore, a circular patch is designed to improve the bandwidth of the X-band antenna. Simulations indicate that the proposed antenna has impedance bandwidths of 46% in X-band (7.5–12 GHz) and 21% in L-band (1.7–2.1 GHz). Moreover, the X-band antenna can scan up to ±60° in the E-plane and ±30° in the H-plane with voltage standing wave ratio (VSWR) below 3. To verify the design method, a shared-aperture antenna prototype, which consists of $6\times6$ X-band elements and one L-band element, has been fabricated and measured. Finally, the measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

A novel coupling-cancellation method by loading planar path is proposed and applied in the millimeter-wave phased array for wide-angle scanning. By employing the improved decoupling stubs with weak radiation first, an extra introduced wideband equal-magnitude and anti-phase path is generated to cancel the inherent coupling path. The principle of the proposed method is investigated by the equivalent circuits and the full-wave simulation. Based on this method, a high-isolation 1-D phased array using low-temperature-cofired ceramic (LTCC) process is designed and fabricated. The planar paths are placed symmetrically between the subarrays and its radiation polarization is coincident with the antenna elements, resulting in high isolation and enhanced boresight radiation null-fill of subarrays. The measured isolation is below 20 dB within the relative bandwidth of 16.7% and the maximum scanning angle is ±60°. Moreover, the proposed method can be expectedly extended to large-scale arrays. [ABSTRACT FROM AUTHOR]

In this article, a novel design of broadband circularly polarized (CP) folded reflectarray (FRA) antenna is proposed. The CP FRA consists of two kinds of metasurfaces (MSs) and a linearly polarized (LP) open waveguide antenna as the feeding source. The bottom MS functions as the main reflector, which is capable of realizing cross-polarization conversion and beam focusing simultaneously. The upper MS is utilized as a subreflector, which could reflect LP wave coming from the feeding source and transmit its orthogonal counterpart into CP wave. For demonstration, the MS-assisted CP FRA antenna is fabricated and measured. Numerical results are consistent with experimental ones, illustrating a peak gain of 24.1 dBi and a peak aperture efficiency of 51% at 9.9 GHz. The 3 dB gain bandwidth and 3 dB axial ratio (AR) bandwidth are achieved as 27.5% (8.8–11.6 GHz) and 43.9% (8–12.5 GHz), respectively. The proposed CP FRA provides a new avenue to realize broadband high-efficiency CP antenna, which may find great potentials in modern wireless communication systems. [ABSTRACT FROM AUTHOR]

This article focused on broadening the azimuth plane scanning range of surface-mounted linear arrays. First, 14 kinds of basic radiation models were theoretically analyzed, and the basic model with a 180° covered main lobe was pointed out. Afterward, a wide-beam surface-mounted antenna was designed using an in-phase-reflection electromagnetic bandgap structure based on the selected element model. Finally, an azimuth plane wide-angle scanning linear array with wide-beam surface-mounted elements was arranged, decoupled, and evaluated. This array can scan its beam in the range of 90° ± 85° in the azimuth plane with a 3 dB gain fluctuation, which verified the effectiveness of the proposed theoretical model. [ABSTRACT FROM AUTHOR]

In this communication, two polarization selective partial reflective decoupling layers (PRDLs) are utilized to mitigate at least two kinds of mutual couplings between two closely spaced dual-polarized dipole antennas. The PRDL is a large-scale model of an actual dielectric board, obtained by arranging a large number of identical conducting obstacles in a regular two-dimensional pattern. The two PRDLs are designed at proper distances from the antenna aperture with well-engineered dielectric constants for two preset polarizations. Each layer is selective to only one polarization by appropriately designing the dimension of the unit cells. Consequently, the two dominant couplings between the two dual-polarized antennas are reduced significantly. The measured isolation between all ports of the two antennas are increased to more than 21 dB, while their reflection coefficients can still maintain in satisfactory status. The radiation patterns, total efficiencies, and envelop correlation coefficients of the proposed antenna, as well as its counterpart without any decoupling measures, are also obtained through measurement, showing significant and reasonable improvements, which further indicates that it has great potential to be extended and applied to 5G MIMO arrays in both base stations and wireless routers. [ABSTRACT FROM AUTHOR]

Improving safety is of general interest in aviation. Flight transponders used in collision avoidance systems advise pilots with information of potential collisions and avoidance resolutions. Some transponders are capable of transmitting the instantaneous position of the vehicle which might be turned off. To prevent autonomous flights from collisions, the transponder signals shall be used to estimate the direction-of-arrival (DoA). Recently, multimode antennas have been investigated for communication and localization purposes. Multimode antennas provide several orthogonal ports on a single radiator surface. This leads to a reduction of space and weight, which is of interest in airborne applications. To perform DoA estimation as well as communication, a suitable channel model is required. In this contribution, a channel model fulfilling the requirements for both multiple-input multiple-output (MIMO) communication and DoA estimation is proposed. This channel model relies on the manifold matrix representation of the UAV under consideration. The derived description of a manifold matrix for the UAV use-case is used for an optimization to achieve a close to omnidirectional radiation pattern. Therefore, different optimization functions are derived and their performance is compared. The results of the optimization using the calculated manifold matrix are verified by measurements taken in an antenna measurement chamber. [ABSTRACT FROM AUTHOR]

A dual-polarized Ku-band and single-polarized Ka-band shared-aperture phased array antenna is proposed in this article. The endfire dipole antenna is designed as the radiating element of both bands. To eliminate the shading effect of the horizontal-polarized Ku-band antenna caused by the common ground, the director is loaded on the Ka-band antenna to increase the height of the equivalent phase center of the Ka-band antenna. The high-order mode of the horizontal-polarized Ku-band antenna is excited when the Ka-band antenna scans to a wide angle in H-plane within the frequency range of 33–34 GHz. An etched square ring is loaded on the Ku-band radiating arm to induce the reverse current to prevent such a high-order mode. The scanning blind spots occur at 33 and 35.8 GHz when the Ka-band antenna scans to 50° in E-plane owing to the mutual coupling between the Ka-band antenna and the vertical-polarized Ku-band antenna. A metallic strip is loaded on the vertical-polarized Ku-band antenna to eliminate the blind spot at 33 GHz. The feeding position of the vertical-polarized Ku-band antenna is elevated to eliminate the blind spot at 35.8 GHz. The periodic cell and finite array are simulated to verify the design proposed in this article. The results demonstrate that the design is effective and the beam-scanning coverage reaches $\pm \mathrm{50}^{\circ }$ at both bands. The active voltage standing wave ratio (VSWR) is not greater than 3.5 at 15–17 and 33–36 GHz in the whole beam-scanning coverage. A prototype of the 4 $\times $ 4 Ku-band and 8 $\times $ 8 Ka-band shared-aperture array is fabricated and measured. The measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

In this work, a UHF broadband surface-independent textile fully woven radio frequency identification (RFID) tag is presented. The antenna is composed of two stacked multilayer fabric pieces in which the shaped conductive and dielectric surfaces are part of the woven structure. In addition, a novel technique for the integration of the RFID chip in the woven structure was developed, providing a maximum integration level and making possible the manufacturing of the tag in a single step using conventional machinery from the textile industry. A tag prototype was experimentally characterized, showing a 12.5 m read range under a $\pm 60\,\, {}\times {}\pm 60^\circ $ angular range, when using a circularly polarized interrogator device with 35.2 dBm effective isotropic radiated power (EIRP). [ABSTRACT FROM AUTHOR]

Antennas for wireless body area networks (WBANs) need to be modeled with adapted methods because the coupling with the body tissue does not allow for a clear separation between antenna and channel. Especially for dynamically varying on-body channels due to changing body poses, e.g., with head-worn antennas, modeling is challenging and design goals for optimal antennas are difficult to determine. Therefore, in this article, the modeling of WBAN channels using spherical wave functions (SWFs) is utilized for antenna de-embedding and for deriving optimal antenna characteristics that maximize the transmission coefficient for the respective channel. It is evaluated how typical factors influencing WBAN channels (different body anatomies, body postures, and varying positions of the communication nodes) can be modeled statistically with SWF. An optimized antenna design is developed based on the derived optimization method, specifically adapted to the channel of on-body links with eye-wear applications. The results with the optimized antenna are compared to other standard antenna designs and validated against measurements. [ABSTRACT FROM AUTHOR]

A design methodology of the dual-band Fabry–Perot-cavity (FPC) antenna is proposed, realizing dual-broadband high gain and keeping the simplicity of one low-profile resonant cavity. A ray optics model is applied to obtain the phase resonance condition for dual-band FPC antennas. The proposed antenna employs a tightly stratified partial-reflective-surface (PRS), an artificial-magnetic-conductor (AMC) ground, and a dual-band microstrip feed. The PRS modulates independently the dual-band reflection coefficient to maintain a large amplitude and a positive phase gradient. Meanwhile, an AMC ground is distinctively employed to compensate for the transmission phase difference of the lower band when the cavity height meets half the wavelength of the upper one, enabling eventually a low-profile uni-cavity. Furthermore, a dual-band microstrip feed with two asymmetric slots is customized as the primary radiator. Detailed electromagnetic studies are carried out to illustrate the operating mechanisms of these components. Finally, a proof-of-concept prototype is fabricated covering the entire global 2.4 and 5 GHz WiFi bands. The measurement results agree well with the simulation, and the 3 dB gain bandwidths of 7.2% and 16.2% with peak gains of 13.6 and 15.0 dBi over two wide bands of 2.42–2.60 and 5.1–6 GHz are achieved, respectively, with a single cavity height of 26.8 mm. [ABSTRACT FROM AUTHOR]

An endfire periodic leaky-wave antenna (LWA) with high gain is presented in this communication, which consists of a series of rhombic elements based on double-sided parallel stripline (DSPSL). The endfire mechanism of the proposed antenna is illustrated by the phase difference of the far field of each arm in the rhombic element. Meanwhile, a tradeoff between the tilted angle $\theta _{0}$ and the width $w$ is found, which assures an optimum transverse aperture for achieving high-gain endfire radiation. Moreover, the improved Hansen–Woodyard (IHW) condition is applied to predict the optimum endfire phase constant. Finally, a prototype is fabricated and tested. The maximum endfire gain of 19.8 dBi is measured at 11.4 GHz, which is close to the simulated and predicted results. The proposed periodic rhombic antenna provides more choice for the modern communication system. [ABSTRACT FROM AUTHOR]

A set of new formulations derived from the cavity model (CM) that significantly improve the design of cylindrical single probe-fed circularly polarized rectangular microstrip antennas (CPRMAs) are presented in this article. Comprehensive analysis shows that differentiation of the dominant modes effective loss tangents in the far-field expressions gives rise to new closed-form design equations suitable for electrically thin antennas, extending the applicability and improving the CM accuracy for electrically small and large radii cylinders. Furthermore, a function is proposed to estimate the minimal number of significant terms needed in the far-field infinite series to portray the fields radiated by the antenna accurately. The proposed formulations are also used as part of an iterative CM-based algorithm that fully solves the issue of synthesizing a cylindrical CPRMA for a user-defined input impedance. Several antenna examples are compared to full-wave simulations to demonstrate the algorithm’s accuracy. To validate the proposed formulations, a right-hand circularly polarized cylindrical antenna prototype is designed and built to operate at 1.575 GHz over a cylinder with a radius of 25 mm. Comparisons between theoretical and experimental results show excellent agreement. [ABSTRACT FROM AUTHOR]

In this communication, a Fabry–Perot (FP) conical beam antenna with multipolarization reconfigurable capability is proposed. A single-layer partially reflective surface (PRS) with circular slots is designed for the prescribed flare angle determined by the height of the FP antenna and resonant frequency. A group of Vivaldi patches with a set of shorting vias around a common central axis on a printed circuit board (PCB) are used as the primary source, which is fed by nested coaxial waveguide. Vivaldi patches coupled with parallel baluns, which are connected to the internal coaxial waveguide, are used to produce a horizontally polarized conical beam. A vertically polarized conical beam can be obtained when the external coaxial waveguide is used to feed the Vivaldi patches. When circularly polarized conical beams are required, the internal and external coaxial waveguides need to be excited at the same time with the same amplitude and the proper phase difference. A prototype of the proposed FP conical beam antenna with multipolarization reconfigurable capability at 12 GHz is designed, fabricated, and measured to verify the concept. The measured results are in good agreement with the simulated ones. A maximum gain of $\ge 12.8$ dBic is achieved with the proposed FP conical beam antenna for the two circular polarization states, with an axial ratio (AR) and impedance bandwidth (IBW) of $\ge 16.7$ % and 8%, respectively. The maximum gain and IBW for the horizontal polarization (HP) and vertical polarization (VP) are $>13.2$ dBi and 9.2%, respectively. [ABSTRACT FROM AUTHOR]

We present a biocompatible high-contrast low-loss antenna (HCLA) designed for efficient into-body radiation for applications as diverse as medical telemetry, sensing, and imaging. The HCLA is wearable with a compact size of 2.62 cm3 and operates across the 1–5 GHz bandwidth. The quasi-bowtie antenna is loaded with a high-contrast (i.e., alternating layers of high- and low-permittivity materials) and low-loss dielectric to improve directivity and gain into the biological tissues. Measurement results at 2.4 GHz are in good agreement with simulations and show 5.72 dB improvement in transmission loss over the most efficient into-body radiator reported in the past. At the high end of the frequency bandwidth, the simulation results for two antennas placed across each other with tissue in between show ~12.5 dB improvement in transmission loss. The HCLA is fabricated with stable, low-loss materials that allow for repeatability and consistency in the fabrication process, thus addressing the limitations of the current state-of-the-art. It is also made from biocompatible materials that enable it to be placed directly on the skin for real-world implementation. In this article, we discuss the operation principle and design of the HCLA, its transmission performance, radiation patterns, and specific absorption rate (SAR). [ABSTRACT FROM AUTHOR]

This communication presents a novel compact tri-band filtering antenna for 5G Sub-6 GHz n41 (2.515–2.675 GHz), n78 (3.4–3.6 GHz), and n79 (4.8–5 GHz) applications. The antenna consists of a central dual-band element and four single-band elements placed around. Simulated results show that the tri-band filtering antenna has an impedance bandwidth ($\vert S_{11}\vert < -10$ dB) of 6.6% (2.51–2.68 GHz), 6.3% (3.39–3.61 GHz), and 5.5% (4.73–5 GHz), covering Chinese 5G Sub-6 GHz band. The distance between single-band elements along both the x-axis and y-axis is $0.31\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength of the center frequency at the lowest band), realizing a compact structure of $0.95\lambda _{0} \times 0.95\lambda _{0} \times 0.2\lambda _{0}$. Since this tightly spaced structure will easily cause strong coupling, additional filtering structure is added, achieving high isolation over 47 dB between the central and the peripheral elements. The final antenna realizes stable gain in all three frequency bands, showing satisfactory in-band average radiation efficiency and high out-of-band gain-suppression level, making it suitable for 5G Sub-6 GHz wireless communication applications. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized (CP) magnetoelectric (ME) dipole antenna loaded with parasitic loop is presented in this communication. The proposed ME dipole antenna is fed through the slot-coupled feeding method, in which a microstrip line is used to couple the energy to the antenna by the slot etched on the ground plane. By introducing a parasitic loop coplanar with the horizontal patch, extra CP modes are generated due to the coupling with the radiation patch. Combining with the original CP mode, the simulated 3 dB axial-ratio (AR) bandwidth is enhanced from 12.2% to 45.8% with an increment of 33.6%. The measured results show that the 10 dB impedance bandwidth is 55.3% (3.4–6.0 GHz) and the 3 dB AR bandwidth is 42.1% (3.62–5.55 GHz). Moreover, the proposed antenna owns flat gain and stable unidirectional radiation patterns within the designated frequency band. [ABSTRACT FROM AUTHOR]

Fabrication tolerances and other types of uncertainties, e.g., the lack of precise knowledge of material parameters, have detrimental effects on the electrical and field performance of antenna systems. In the case of input characteristics, these are particularly noticeable for narrowband and multiband antennas where deviations of geometry parameters from their nominal values lead to frequency shifts of the operating frequency bands. Improving design robustness is therefore important yet challenging. On the one hand, it is numerically demanding as it involves uncertainty quantification (UQ), in particular, estimation and improvement of appropriately defined statistical performance metrics. On the other hand, it has to be carried out at the level of full-wave electromagnetic (EM) simulation models, which incurs considerable computational expenses. Executing UQ tasks at practically acceptable costs can be realized using surrogate modeling methods; however, the construction of reliable metamodels is hindered by the curse of dimensionality. This article proposes a novel approach to the robust design of antenna structures, where the task is formulated to increase the maximum values of parameter deviations for which 100% fabrication yield is ensured. Low cost of the optimization process is enabled by incorporating feature-based regression models for rapid yield estimation, as well as the employment of the trust-region framework for adaptive adjustment of design relocation but also as a convergence safeguard. Our methodology is validated using three microstrip antennas, including two dual-band and a triple-band structure. [ABSTRACT FROM AUTHOR]

In this article, a novel polarization reconfigurable antenna based on the Moiré effect is proposed. The presented design exploits substantial changes in the overlapped Moiré patterns to minimize the needed actuation for antenna reconfiguration. The novel antenna design is based on stacking two circular FR4 substrates on top of a truncated edge rectangular patch antenna. The top layers of both the substrates are milled into horizontal stripes forming the Moiré patterns. One of these substrates is fixed with respect to the antenna, while the second one rotates with respect to the fixed substrate. Upon rotation, these stripes from the two substrates overlap in pattern, which shapes the antenna. As a result, the antenna design is capable of switching its polarization scheme between vertical, horizontal, and circular with left-hand orientation. In addition, the Moiré patterns can also enhance the directivity and gain of the proposed antenna. The reconfiguration’s mechanical actuation is achieved via a nontraditional ratchet mechanism that uses shape memory alloys (SMAs). This realized actuation system is fast, flexible in its positioning, has low energy expenditure, and minimizes interference with antenna operation. An antenna prototype is fabricated and tested where measured results match the simulated performance. [ABSTRACT FROM AUTHOR]

In this article, a multielement fully decoupled linearly placed inverted-F antenna (IFA) array is proposed for mobile terminals. A hybrid decoupling method is used to mitigate the mixed types of mutual couplings among the multiple IFAs: introducing multiple decoupling capacitors for the couplings of two back-to-back IFA pairs and T-shaped mode transformers for the remaining couplings. The decoupling capacitors not only decouple the back-to-back IFA pairs but also broaden the impedance bandwidth of each IFA. The T-shaped mode transformer transforms the concerned antenna from an IFA mode into a balanced loop mode, preventing the induced current on the victim IFAs of the face-to-face and back-to-face pairs. One four-element example and one eight-element example are designed and measured to justify the proposed decoupling concept. The measured results of the four-element IFAs show that after decoupling, all the six mutual couplings among the four IFAs are reduced by about 10 dB from 3.3 to 3.8 GHz, with average total efficiencies throughout the band improving from 57% to 72% for IFA 1 and from 47% to 55% for IFA 2. An eight-element IFA array is built utilizing the pattern diversity of two proposed four-element IFA blocks, achieving inter-block isolation of better than 20 dB. And a six-element linear IFA array is also designed to prove the generality of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, a millimeter-wave (mmWave) endfire phased array antenna with ±45° linear polarizations is proposed for fifth generation (5G)/B5G mobile communications. The proposed antenna achieves ±45° polarizations by utilizing a modified substrate integrated waveguide (SIW) slot polarizer. The polarizer generates dual orthogonal modes with equal amplitudes and a 0°/180° phase difference, thereby yielding $+ 45^{\circ }/- 45^{\circ }$ -polarization radiated waves in the far field. In a practical metal-framed mobile phone environment, the ±45 polarizations are verified to provide more balanced radiation patterns and, consequently, a higher polarization-multiple input multiple output (MIMO) efficiency. A prototype of the proposed 1 $\times $ 4 array is fabricated and measured, achieving a −10 dB impedance bandwidth of 23.4–30.0 GHz (covers 5G band of n257/n258), with an isolation better than 15.6 dB and a realized gain above 8.9 dBi in the operating bandwidth. A peak gain of 11.4 dBi and a 3 dB scanning range of 87° can be observed at 27.0 GHz. Furthermore, the prototype is characterized on a metal-framed mobile phone platform, experimentally demonstrating its superiority to conventional vertical/horizontal polarized (V-/H-pol) arrays. The validated advantages of the balanced radiation patterns and robust impedance matching make the proposed ±45°-polarization endfire antenna array a promising candidate for mobile terminals in the era of 5G/B5G. [ABSTRACT FROM AUTHOR]

The whip antennas used for HF/VHF band communication on the vehicles or ships are generally larger in length and diameter. It would be of great significance if it could be easily hidden from microwave detection radar searches. Aiming at the lower RCS of whip antenna in X-band and maintaining the original impedance and radiation characteristics under high-power input, we propose a whip antenna integrating a novel curved artificial magnetic conductor (AMC) to achieve the RCS reduction in X-band. The backscattering of the cylinder can be dispersed by using the 180° phase difference cancellation principle of different AMC structures, and the mechanism is demonstrated by simulation and experiment. The measurements are in good agreement with the simulations, and the measurement results indicate that in the band of 8–12 GHz, the backward RCS is reduced by an average of 11.2 dBsm in VV polarization and by 10.2 dBsm in HH polarization. Moreover, the proposed whip antenna can be applied to high-power HF/VHF transmitting systems, and the withstand voltage can reach 15 kV (continuous output above 10 kW). This method has important theoretical significance and practical values for the whip antenna in practical engineering applications. [ABSTRACT FROM AUTHOR]

In the near-field meta-steering method, the near electric-field phase distribution is dynamically altered by rotating a pair of phase-gradient metasurfaces that are typically made out of dielectric lattices or metal patterns printed on bonded dielectric substrates. As a lightweight alternate, a new class of fully metallic metasurfaces (MMs) is proposed in this article. The lack of dielectrics not only substantially reduces the cost and weight but also increases its potential in space and high-power applications. More importantly, the new MMs are designed such that they can be made by cutting narrow slots in fully planar thin metal sheets, retaining structural rigidity while reducing the complexity, cost, and weight. The same MM works for any polarization. Each cell in the new MMs has close to ideal phase shift and transmission magnitude greater than −0.9 dB. A prototype was designed and fabricated to validate this MM-based beam-steering concept in the Ku-band. The maximum measured steering range in zenith is ±42°, with a full 360° steering in the azimuth. The measured 3 dB gain bandwidth is 700–800 MHz (5.6%–6.4%), and the measured gain variation (scan loss) when steering over the whole range is 2.2–4.5 dB. The weight density and thickness of each MM are 0.88 g/cm2 and $0.8\lambda _{0}$ , respectively. Including the feed, the total antenna height is $4.9\lambda _{0}$. [ABSTRACT FROM AUTHOR]

In this article, a wideband aperture-coupled stacked-patch (ACSP) antenna on a flexible material for wireless applications at the WR-08 band is presented. It is shown that conventional designs of ACSP fail to achieve a large bandwidth at this frequency range, and a novel design methodology is proposed. We first propose a broadband impedance matching between the input port and the slot aperture based on two-section wideband distributed network (TWBDN). We also propose a TWBDN matched stacked patch (TMSP) network based on constant VSWR circles to attain broadband matching between the slot aperture and patches in an ACSP. To facilitate the measurements, a novel low-loss transition from a ground-signal-ground (GSG) port to a feedline is proposed. The proposed structure suppresses surface waves induced in the WR-08 band by placing via arrays around the feedline, which largely reduces unwanted resonance modes, thereby leading to uniformly high radiation efficiency across the band. The measured results of the fabricated antenna closely follow the simulations, and a measured peak gain of 7.95 dBi and $S_{11}\leq -10$ dB across a wide frequency range from 90 to 128.5 GHz is achieved. [ABSTRACT FROM AUTHOR]

A compact high gain omnidirectional horizontally polarized (OHP) antenna array is proposed in this communication. The theoretical calculations prove that a slender aperture with uniform field distribution can achieve OHP radiation with high directivity. The rectangular patch antenna operating in TM10 mode is employed to obtain an element with the specific field distribution. To extend the electrical length of the aperture, the element is elongated, and four collinear elements are integrated as an array without any redundant structures. Benefitted from the reasonable electric field distribution and concise configuration, the aperture efficiency is significantly improved. Therefore, the proposed antenna can achieve high gain OHP radiation in a compact size. The overall dimension of the antenna array is $4.62\lambda \times 0.22\lambda \times 0.07\lambda $ ($\lambda $ is the free space wavelength at the center frequency). Measured results verify that the impedance bandwidth of the array covers 5.46–6.13 GHz with a relative bandwidth of 11.6%, a maximum realized gain of 11 dBi, and good omnidirectional characteristics with a gain variation of less than 3 dB in the entire operating bandwidth. [ABSTRACT FROM AUTHOR]

In this work, we present a novel analytical model for the magnetic field in through-the-Earth (TTE) communications. The modeling approach is based on dyadic Green’s functions to compute impressed and scattered fields in a multilayered structure. Its performance is assessed through comparisons with previous models, measurements, and simulations of magnetic field. The great advantages of the proposed approach in relation to the previous ones are its flexibility in the positioning and direction of antennas and the unlimited number of layers of soil. Moreover, this approach can be more accurate than classical ones in scenarios where the soil has a high conductivity below the antenna in an uplink scenario. [ABSTRACT FROM AUTHOR]

An eight-port planar leaky-wave antenna (LWA) is proposed. This antenna has the capability of beam steering at an elevation angle by changing the frequency at eight azimuth angles. The antenna is planar and has an array of ring slots embedded in a microstrip parallel plate waveguide. We investigate the simulation and experimental results. The measured results have good agreement with the simulation and confirmed the leaky-wave (LW) concept. The proposed antenna yields an attractive, simple, and cost-effective beam scanning over the 3-D space. [ABSTRACT FROM AUTHOR]

A novel microstrip magnetic dipole (MMD) antenna is proposed to produce a high broadside gain utilizing slot-loaded high-order mode. Conventionally, MMD antennas yield patch currents in opposite directions when resonating in high-order modes. Radiations of these currents are out of phase and neutralize in the broadside direction, resulting in a low broadside gain. This work presents a method to reverse the out-of-phase currents by loading slots. An in-depth analysis is conducted to show the mechanism and effect of the slots. The proposed method is applied to a high-gain MMD antenna design for further gain enhancement. The improved antenna produces a large impedance bandwidth of 17.8% (5.1–6.1 GHz). A maximum broadside gain of 14.8 dBi is achieved within this bandwidth. The proposed antenna is promising for extending signal coverage of WLAN 5.5 GHz applications. [ABSTRACT FROM AUTHOR]