Showing papers in "IEEE Transactions on Antennas and Propagation in 2021"
TL;DR: In this article, a general decoupling method based on a new perspective of common mode (CM) and differential mode (DM) cancellation is proposed for two closely spaced antennas, where the mutual coupling effect can be analyzed and solved by exciting them simultaneously with in-phase and out-of-phase signals.
Abstract: In this article, a general decoupling method based on a new perspective of common mode (CM) and differential mode (DM) cancellation is proposed. For two closely spaced antennas, the mutual coupling effect can be analyzed and solved by exciting them simultaneously with in-phase (CM) and out-of-phase (DM) signals. It is theoretically proved that, if CM and DM impedances are the same, the mutual coupling effect between two separated antennas can be totally eliminated. Therefore, we can solve the coupling problem by CM and DM impedance analysis and exploit the unique field properties of characteristic modes to assist in antenna decoupling in a physical intuitive way. To validate the feasibility of this method, two practical design examples, including the decoupling between closely spaced dipole antennas and planar inverted-F antennas, are proposed. Both design examples have demonstrated that the proposed method can provide a systemic design guideline for antenna decoupling and achieve better decoupling performance compared to the conventional decoupling techniques. We forecast the proposed decoupling scheme, with a simplified decoupling procedure, has great potential for the applications of antenna arrays and multi-input multi-output (MIMO) systems.
105 citations
TL;DR: In this paper, a superstrate-based decoupling method was proposed to reduce the mutual coupling between two closely packed dipole antennas while maintaining cross-polarization suppression.
Abstract: A ceramic superstrate-based decoupling method (CSDM) is proposed to reduce the mutual coupling between two closely packed dipole antennas while maintaining cross-polarization suppression. Compared with other superstrate-based methods, this proposed method can effectively reduce the mutual coupling between the antennas without using any periodic structures on the superstrate. The ceramic superstrate is a 2 mm thin slab with a relative dielectric constant of 20.5 and is suspended over the antennas coupled in H-plane with the spacing of only 0.28 wavelength at 3.5 GHz. It is demonstrated by both simulation and measurement that the isolation between two dipole antennas can be improved from 10 to more than 25 dB within the operation band while their reflection coefficients remain to be below −10 dB after the ceramic superstrate is introduced. The radiation patterns of the antenna maintain stable at different operation frequencies within the band of interest and the peak gain has increased by around 1.5 dB. Meanwhile, the total efficiency is enhanced by about 15% and the envelope correlation coefficient (ECC) between the two antennas is reduced from 0.7 to 0.4.
82 citations
TL;DR: This article presents the theoretical considerations and the design evolution of a proof-of-concept reconfigurable metasurface, primarily used as a tunable microwave absorber, but also as a wavefront manipulation and polarization conversion device in reflection.
Abstract: In this article, we present the theoretical considerations and the design evolution of a proof-of-concept reconfigurable metasurface, primarily used as a tunable microwave absorber, but also as a wavefront manipulation and polarization conversion device in reflection. We outline the design evolution and all considerations taken into account, from the selection of patch shape, unit cell size, and substrate to the topology of the structure that realizes the desired tunability. The presented design conforms to fabrication restrictions and is codesigned to work with an integrated circuit (IC) chip for providing tunable complex loads to the metasurface, using a commercially available semiconductor process. The proposed structure can perform multiple tunable functionalities by appropriately biasing the IC. Perfect absorption for a wide range of incidence angles of both linear polarization states, accommodating a spectral range in the vicinity of 5 GHz, with potential also for wavefront control, exemplified via anomalous reflection and polarization conversion. The end vision is for such a design to be scalable and deployable as a practical HyperSurface, i.e., an intelligent multifunctional metasurface capable of concurrent reconfigurable functionalities: absorption, beam steering, polarization conversion, wavefront shaping, holography, and sensing.
81 citations
TL;DR: In this article, an inductance-based decoupling scheme is proposed to reduce the mutual coupling between extremely closely spaced microstrip antennas by inserting a lumped inductance in between.
Abstract: In this article, an inductance-based decoupling scheme is proposed to reduce the mutual coupling between extremely closely spaced microstrip antennas. The original strong coupling can be effectively suppressed by simply inserting a lumped inductance in between. To offer a systemic design guideline for this decoupling strategy, a mode cancellation method, based on the synthesis of common mode (CM) and differential mode (DM), is proposed. The inserted inductance plays a role of tuning CM and DM impedances to a similar status, which has an equivalent decoupling effect according to the theory of microwave network. Alternatively, the lumped inductance could also be replaced by an inductive connecting strip for a concise topology. To validate the proposed decoupling concept, a prototype is simulated, fabricated, and measured. The experimental results show that the poor isolation of 5 dB is improved to better than 15.4 dB across the entire matched bandwidth of 2.394–2.530 GHz, with an extremely close edge-to-edge distance of $0.016~\lambda _{0}$ and center-to-center distance of $0.44~\lambda _{0}$ . Furthermore, the validation of extending to large-scale 1-D and 2-D arrays is also discussed. Featuring simple structure, compressed dimension, strong-coupling suppression, and good radiation performance, the proposed decoupling scheme possesses promising potential for antenna array applications.
80 citations
TL;DR: In this paper, a new technique for the accurate design of metasurface reflectarrays is presented, which accounts for mutual coupling between distinct reflectarray elements Contrary to the conventional approach, no local periodicity assumptions are made in the design of the reflect array elements, and is shown to more accurately predict the far field patterns of a reflectarray.
Abstract: This article presents a new technique for the accurate design of metasurface reflectarrays The design technique accounts for mutual coupling between distinct reflectarray elements Contrary to the conventional approach, no local periodicity assumptions are made in the design of the reflectarray elements The reflectarray considered consists of a subwavelength-patterned metallic cladding (metasurface) over a ground plane The cladding is homogenized and modeled as an inhomogeneous impedance sheet The inhomogeneous impedance sheet is designed through the solution of an integral equation The integral equation is solved using the method of moments In the design, both the scattered field amplitude and phase are specified The scattered field amplitude is chosen to conserve local power density at the reflectarray surface This condition results in complex sheet impedances An optimization technique is subsequently used to obtain a purely reactive sheet which gives the same performance as the complex sheet The process used to extract the reactance of printed geometries is detailed An example of a $20 \lambda $ wide array is presented All the results are validated through COMSOL Multiphysics simulations The presented design approach is compared to the conventional approach and is shown to more accurately predict the far-field patterns of a reflectarray
76 citations
TL;DR: In this article, an electromagnetic transparent antenna element is proposed for dual-band shared-aperture 5G MIMO base station antenna array developments, which is inspired by the element of a typical wide-angle bandpass frequency selective surface (FSS).
Abstract: An electromagnetic transparent antenna element is proposed for dual-band shared-aperture fifth-generation (5G) MIMO base station antenna array developments. The antenna element that operates in the low-frequency band (LB) of 1.8–2.7 GHz is placed above the aperture of the antenna array that operates in the high-frequency band (HB) of 3.3–3.8 GHz. Because of this antenna array configuration, the antenna elements in the LB have to be transparent to the electromagnetic waves radiated by the HB antenna array. This kind of electromagnetic transparent antenna element allows the HB antenna array working properly in the dual-band shared-aperture antenna array configuration. In this work, the electromagnetic transparent antenna element is inspired by the element of a typical wide-angle bandpass frequency selective surface (FSS). The radiation performance of the electromagnetic transparent antenna element at the LB is realized by properly combining the wide-angle bandpass FSS elements. A dual-band dual-polarized shared-aperture antenna array is then developed to demonstrate the concept and design. The experimental result validates the stable radiation patterns of each antenna element in both LB and HB. It indicates the proposed approach is promising for 5G MIMO base station antenna array developments.
72 citations
TL;DR: A wideband decoupling technique to suppress the strong coupling between two extremely closely spaced open-slot antennas and implements a wideband integrated slot antenna pair for fifth-generation (5G) metal-rimmed smartphones has great potential for future 5G smartphones.
Abstract: This communication proposes a wideband decoupling technique to suppress the strong coupling between two extremely closely spaced open-slot antennas and implements a wideband integrated slot antenna pair for fifth-generation (5G) metal-rimmed smartphones. By simply inserting a connecting line between two closely spaced open-slot antennas, a top slot structure can be constituted with odd- and even-mode resonances in the lower and higher bands, respectively, to cancel the original strong mutual coupling. In addition to the decoupling effect, the top slot can also expand the effective radiation aperture of the antenna pair for the bandwidth improvement. The proposed slot antenna pair, with a compact footprint of $28 \,\, \times 7\,\,\times1.8$ mm3, shows good impedance matching, isolated and diversity performance across 3.3–5.0 GHz. Then, an $8 \times 8$ multiple-input multiple-output (MIMO) system, constituted by four sets of slot antenna pairs, is simulated, fabricated, and measured. Both the simulated and experimental results show that the $8 \times 8$ MIMO system can offer isolations of better than 10.8 dB and envelope correlation coefficients (ECCs) of less than 0.14 between all eight ports across 3.3–5.0 GHz. Also, a total efficiency of 55.0%–83.1% and 52.5%–83.1% is achieved for Ant1 and Ant2, respectively. Featuring wide bandwidth, compact size, high integration level, and metal rim compatibility, we forecast the proposed solution has great potential for future 5G smartphones.
70 citations
TL;DR: In this article, a low-profile broadband planar circularly polarized folded transmitarray antenna (CPFTA) based on well-designed top and bottom metasurfaces (MSs) is proposed.
Abstract: We propose a low-profile broadband planar circularly polarized folded transmitarray antenna (CPFTA) based on well-designed top and bottom metasurfaces (MSs). The top MS is employed to reflect the $x$ -polarized wave as a ground and, at the same time, to convert the $y$ -polarized wave into circularly polarized waves with arbitrary phase shifts in the operation band. A bottom MS is applied to reflect the incident wave and twist its polarization by 90°. The whole CPFTA, including the feeding source of microstrip antenna, and the top and bottom MSs can be fully integrated and fabricated using low-cost printed circuit board technology. Both simulated and measured results demonstrate significant advantages of the proposed antenna, including broad bandwidth, high gain, lower profile, planar geometry, and easy integration. The fabricated sample shows 3 dB axial ratio (AR) bandwidth of 23.2%, 3 dBi gain bandwidth of 11.6%, and the maximum gain of 22.8 dBi at 10.3 GHz with the antenna efficiency of 21.8%. The proposed CPFTA is promising for applications in satellite communications with circularly polarized antennas.
68 citations
TL;DR: In this article, a co-linearly polarized microstrip antenna with identical radiation properties is proposed and validated for in-band full-duplex systems by exploring a fence-strip resonator (FSR) in the central plane of a patch, achieving good isolation between the transmitting and receiving ports.
Abstract: A compact co-linearly polarized microstrip antenna with identical radiation properties is proposed and validated for in-band full-duplex systems. By exploring a fence-strip resonator (FSR) in the central plane of a patch, good isolation is achieved between the transmitting and receiving ports. The proposed FSR consists of a metallic vias fence and a strip with a distance away from the ground, performing as a pair of distributed inductor and capacitor. When the FSR is resonating, the radiating current is concentrated in the half part of the patch, performing at its half-TM10 mode with high port isolation. To validate the proposed antenna, a prototype with the size of $0.25\lambda _{0} \times 0.25\lambda _{0} \times 0.04\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength at center frequency) has been fabricated and characterized, with experiments consistent well with simulations. A measured port isolation higher than 20 dB is achieved over the operating bandwidth of 2.40–2.52 GHz with the maximum of 30 dB. The proposed antenna is with the merits of compact size, low profile, simple feed, and planar-integrated structure for in-band full-duplex systems.
66 citations
TL;DR: This large-aperture reflectarray shows promising applications for tracking and detecting systems and critical design issues, including element modeling, subarray optimization, and feed horn selection, are investigated to achieve good radiation performance.
Abstract: A large-scale 1-bit reconfigurable reflectarray with the feature of fast steerable monopulse patterns has been designed and tested at ${X}$ -band. The reflectarray element integrates one PIN diode to reconfigure the reflective phase between 0° and 180°. The entire reflectarray is composed of $160\times64$ elements, with a total size of 2.56 m $\times1.024$ m. Critical design issues, including element modeling, subarray optimization, and feed horn selection, are investigated to achieve good radiation performance. For the purpose of realizing fast beam steering, 160 field-programmable gate arrays (FPGAs) are adopted to control “ON/OFF” states of every p-i-n diodes in parallel. Digital beam forming methods have been applied to scan both the sum and difference beams. The reflectarray has been fabricated and measured in an anechoic chamber, and a high gain (37.4 dBi) with relatively good aperture efficiency (17.1%) has been realized in such a large-aperture size. Precise monopulse beam steering within ±60° azimuth range has been achieved with the switching time of only $2~\mu \text{s}$ . This large-aperture reflectarray shows promising applications for tracking and detecting systems.
65 citations
TL;DR: A novel understanding perspective is proposed to better distinguish the two kinds of time and based on the multiple input multiple output (MIMO) scheme with multiple matched filters at receiver, the prerequisite for exploring the range-dependent property of FDA is demonstrated.
Abstract: Owing to the property of range–angle-dependent beampattern, frequency diverse array (FDA) has promising application potentials in radar field. Many studies have been reported to solve the time-variant problem of FDA. However, there is a misconception between the time index within pulse and the actual time, which misleads the theoretical analysis for FDA. In this article, a novel understanding perspective is proposed to better distinguish the two kinds of time. The exact time–range and frequency–phase relationships are presented. In the sequel, the correction analysis about the operation theories of FDA considering the factor of time is presented along with the accurate understanding about the range–angle beampattern. Furthermore, based on the multiple input multiple output (MIMO) scheme with multiple matched filters at receiver, the prerequisite for exploring the range-dependent property of FDA is demonstrated. Simulations demonstrate the validity of theoretical results.
TL;DR: In this paper, a planar array with resistance-loaded metallic cross patterns and a vertical periodic crossed mesh array with resistive metallic ring patterns were used to improve the wide-angle polarization-independent absorption.
Abstract: In this article, by deliberately controlling multiple resistive electric and magnetic resonances in terms of dispersion and dissipation, a low-profile, wideband, microwave metamaterial absorber with wide-angle and polarization-independent responses is proposed. The proposed absorber comprises a planar array with resistance-loaded metallic cross patterns, and a vertical periodic crossed mesh array with resistance-loaded metallic ring patterns. The vertical periodic crossed mesh array was inserted between the planar array and the metal ground to improve the wide-angle polarization-independent absorption. The involved dispersion-engineered design strategy for angular- and polarization-insensitive responses is described with numerical evidences and electromagnetic response behaviors. A proof-of-concept absorber was fabricated and measured for verification. At quasi-normal incidence, the measured bandwidth characterized by more than 90% absorption was 2.11–3.89 GHz, i.e., a fractional bandwidth (FBW) of 59.3%. At the incident angle of 50°, the FBW of the absorption larger than 90% was 48.6%. The absorber was thin with a thickness of 13 mm, corresponding to $0.09\lambda _{0}$ at the lowest operating frequency. The numerical and experimental results demonstrated that our proposed strategy provides an effective way to achieve wide-angle and polarization-independent responses in a broadband; these responses are very promising for most strategic applications.
TL;DR: The object covered by the metasurface is hence perfectly camouflaged to a foe radar and can be detected by a friend radar possessing the spread-spectrum demodulation key corresponding to the metAsurface modulation, and this detection is robust to interfering signals.
Abstract: This article presents the concept of spread-spectrum selective camouflaging based on time-modulated metasurface. The spectrum spreading is realized by switching the metasurface between the reflective states of a perfect electric conductor (PEC) mirror and a perfect magnetic conductor (PMC) mirror, using an array of microstrip patches connected to the ground via diode switches, according to a periodic pseudorandom noise sequence. As the spectrum spreading induces a drastic reduction of the power spectral density of the signal, the level of the scattered wave falls below the noise floor of the interrogating radar, and the object covered by the metasurface is hence perfectly camouflaged to a foe radar. Moreover, the object can be detected by a friend radar possessing the spread-spectrum demodulation key corresponding to the metasurface modulation, and this detection is robust to interfering signals. The proposed system is analyzed theoretically and demonstrated by both simulation and experimental results.
TL;DR: In this paper, an end-fire dual-polarized phased antenna array with small ground clearance is proposed for the 5G millimeter-wave (mmW) applications with a wide bandwidth in which each antenna element consists of a dipole fed by a microstrip line for horizontal polarization and an H-plane horn using substrate-integrated waveguide (SIW) for vertical polarization.
Abstract: In this article, an endfire dual-polarized phased antenna array with small ground clearance is proposed for the fifth-generation (5G) millimeter-wave (mmW) applications with a wide bandwidth In this array, each antenna element consists of a dipole fed by a microstrip line for horizontal polarization and an H-plane horn using substrate-integrated waveguide (SIW) for vertical polarization To achieve a wide bandwidth for vertical polarization, two metal vias are added at the aperture of the horn antenna Then, a four-element antenna array is designed by partially overlapping the aperture of each horn element A prototype has been fabricated using multilayer printed circuit board (PCB) process The measured results agree well with the simulated ones The antenna is with an impedance bandwidth of $\vert \text{S}_{11}\vert dB from 244 to 295 GHz for both polarizations The maximum gains of vertical and horizontal polarizations are 916 and 927 dBi, with the scanning angle from −34° to 33° for both polarizations with gain deterioration less than 3 dB The proposed antenna is a promising solution for 5G mmW cellphones or antenna-in-package applications
TL;DR: In this article, a wideband and highly-integrated quad-element multiple-input multiple-output (MIMO) antenna is proposed for the first time, to adapt to the size-limited environment in fifth-generation (5G) smartphones.
Abstract: In this article, a wideband and highly-integrated quad-element multiple-input multiple-output (MIMO) antenna is proposed for the first time, to adapt to the size-limited environment in fifth-generation (5G) smartphones. First, the wideband decoupling between two extremely closely-spaced open-slot antennas with face-to-face and back-to-back configurations are investigated. Then, based on the complementary antenna pairs, wideband integrated quad-element MIMO antennas are implemented by the ingenious combination of these antenna pairs. For validation, an $8 \times 8$ MIMO system, constituted by two sets of integrated quad-antenna configurations, is simulated, fabricated, and measured. Both the simulated and measured results show that the $8\times 8$ MIMO system can provide isolation of better than 10 dB between any two ports and a total antenna efficiency of 52.8%–70.8%/40.5%–75.0% across 3.3–5.0 GHz. Compared with the existing integrated quad-antenna design schemes, the proposed solution can expand the bandwidth from less than 200 to 1700 MHz, covering the entire 5G N77, N78, and N79 bands. In addition to the integrated quad-antenna design, further extension to integrated multiantenna configurations is also discussed by the flexible combination of complementary antenna pairs, which paves the way for future higher-order MIMO system in smartphones.
TL;DR: Numerical results prove that the proposed FICLM outperforms the method of moments (MoM) in terms of both computational speed and accuracy by use of reference data with a higher precision.
Abstract: This article proposes a learning-based noniterative method to solve electromagnetic (EM) scattering problems utilizing pix2pix, a popular generative adversarial network (GAN). Instead of calculating induced currents directly from a matrix inversion, a forward-induced current learning method (FICLM) is introduced to calculate the induced current through a neural-network mapping. The scattered fields can be further calculated through a multiplication of the Green’s function with the predicted induced currents. Inspired by wave physics of scattering problems, we have designed three kinds of input schemes, covering different combinations of the given incident field and permittivity contrast, to evaluate the performance of the FICLM model under both single-incidence and multi-incidence cases. Numerical results prove that the proposed FICLM outperforms the method of moments (MoM) in terms of both computational speed and accuracy by use of reference data with a higher precision. The FICLM with the direct sum of permittivity contrast and a so-called Born-type induced current, achieves the best calculation accuracy and generalization capability compared to the other two inputs. The comparison with other types of neural networks, such as U-net, also demonstrates the superior performance of FICLM for dealing with complex scatterers due to the use of adversarial framework in pix2pix. The proposed method paves a new way for the fast solution of EM-scattering problems through deep learning techniques.
TL;DR: A circularly polarized (CP) reflectarray with 2D electronically steerable beam is reported in this article, which is realized using a circular patch-based structure with p-i-n diodes incorporated.
Abstract: A circularly polarized (CP) reflectarray with 2-D electronically steerable beam is reported The reconfigurable CP reflectarray element is realized using a circular-patch-based structure with p-i-n diodes incorporated A new electronical phase manipulation method is proposed based on the element rotation technique and by additionally exploiting symmetries in the field distribution of the element’s fundamental resonant mode Element rotation can be equivalently achieved by altering the biasing voltage and changing the electromagnetic behavior of the reflective phasing cell The proposed design approach brings about simplification in element configuration, leading to a reduction in the number of required diodes by a factor of one half Practical concerns of the element and biasing complexity as well as the insertion loss are, therefore, well-handled A fully functional $16\times16$ reconfigurable CP reflectarray is designed, fabricated, and tested to validate the concept Good beam focusing and 2-D dynamic beam steering capabilities are confirmed through experiments, along with decent polarization purity and comparatively high aperture efficiency The proposed simple and robust design could be attractive for implementing lightweight, low-cost, and large-scale 2-D reconfigurable CP reflectarrays
TL;DR: In this paper, a high-efficiency conformal transmit array with ultrathin dual-layer Huygens element is developed, which consists of "I" shape patches for magnetic response and "T" shape stubs for electric response printed on two metal layers of a single substrate with only 0.5 mm thickness.
Abstract: A high-efficiency conformal transmitarray with ultrathin dual-layer Huygens element is developed. The element consists of “I” shape patches for magnetic response and “T” shape stubs for electric response printed on two metal layers of a single substrate with only 0.5 mm thickness ( $\lambda _{0}$ /60 at 10 GHz). By tuning the magnetic and electric responses, the transmitting phase of the element can be changed. Eight elements are designed to cover quantized 360° phase range with a maximal 1.67 dB loss. Then, the proposed elements are employed in a small conformal transmitarray design. To improve the antenna efficiency, the elements’ dimensions are calculated by considering the oblique incidence effects. Finally, a cylindrically conformal transmitarray with a larger aperture size is simulated, fabricated, and measured. It can achieve a measured gain of 20.6 dBi with a 47% aperture efficiency.
TL;DR: In this paper, a dual-polarized planar phased array with high polarization isolation and low crosspolarization is presented operating from 4 to 18 GHz, i.e., 4.5:1.
Abstract: In this article, a dual-polarized planar phased array with high polarization isolation and low cross-polarization is presented operating from 4 to 18 GHz, i.e., 4.5:1. The proposed array is comprised of tightly coupled dipoles with integrated coupled-Marchand baluns. To improve the uniformity of fields distributed on the array, the center-feeding dipole is used in this design instead of the conventional edge-feeding one at first. Then, the outer conductors of the feed are composed of a group of shorted vias with the proper number and position. Based on these methods, the output balance of the balun is significantly improved, resulting in high isolation between ports with different polarization modes. Furthermore, this feed has a natural ability to suppress the D-plane common mode resonance. The capacitive metallic annular plate over adjacent radiating elements and the thick aluminum plate with an air cavity placed under the array are employed together to suppress the in-band coupled-loop modes. The infinite array simulation indicates that the array can achieve transmit (Tx)/receive (Rx) isolation more than 48 dB at broadside. Isolation better than 32 and 30 dB can be achieved when scanning to 45° in E-/H-planes and 60° in E-plane, respectively. The cross-polarization level is below −54 dB at broadside and remains below −29 dB when scanning to 60° in E-plane as well as 45° in H-plane. A $12\times12$ dual-polarized antenna array is fabricated and measured to validate the correctness of this design. This type of antenna can be applied in wideband simultaneous transmit and receive (STAR) monostatic systems.
TL;DR: A fully textile rectenna for ultralow-power sub-LaTeX/cm2 applications and efficiently receives power from mismatched polarization and with a 360° half-power beamwidth.
Abstract: Despite the recent advances in textile antennas, in complete systems such as a rectenna, the efficiency of fully textile solutions has been over 46% lower than hybrid textile/rigid implementations. This article presents a fully textile rectenna for ultralow-power sub- $\mu \text{W}$ /cm2 applications. A dual-polarized omnidirectional low-profile textile antenna is presented. The rectenna is based on a compact inductively matched rectifier. The textile-based rectifier occupies 0.22 cm2 and achieves a state-of-the-art power conversion efficiency (PCE) of 41.8% at −20 dBm, at 820 MHz, despite its lossy substrate. A triple-band rectifier is then designed and fabricated to show the scalability of the matching approach. The rectifier is characterized using a new figure of merit “average PCE” over a time period while charging a capacitor. Time-varying S-parameters are used to quantify the impact of the capacitor’s charge on the impedance matching. The rectifier directly charges a 1.32 mF capacitor up to 1 V in 0.41 and 4.5 s from 10 and 0 dBm, respectively. Wireless testing of the proposed rectenna demonstrates over 50% and 40% (PCE) below $1~\mu \text{W}$ /cm2 in space and on-body, respectively. The rectenna efficiently receives power from mismatched polarization and with a 360° half-power beamwidth.
TL;DR: In this article, an efficient wideband polarization-rotation thin metasurface based on oval pattern is presented to manipulate the polarization of incident electromagnetic waves in reflect band, where the oval pattern was split by strip lines to outperform the results.
Abstract: An efficient wideband polarization-rotation thin metasurface based on oval pattern is presented. The aim of this structure is to manipulate the polarization of incident electromagnetic waves in reflect band. The oval pattern is split by strip lines to outperform the results. It is shown that the proposed polarization converter converts the incident linearly or circularly polarized waves into orthogonal counterpart over a frequency band of 10.2–20.5 GHz. A prototype of the proposed structure is fabricated to validate the numerical simulation. The experimental and simulation results confirm that polarization conversion ratio (PCR) is greater than 90% at the same frequency band with high stability to oblique incidence angle. Numerical simulation reveals that the strong electric and magnetic resonances between top and bottom layers lead to wideband polarization conversion. Equivalent impedance surface method is discussed to further analysis the polarization conversion mechanism.
TL;DR: In this article, a dual-polarized highly-folded self-grounded Bowtie antenna that is excited through I-shaped slots is proposed for applications in sub-6GHz 5G MIMO antenna systems.
Abstract: In this paper, a novel dual-polarized highly-folded self-grounded Bowtie antenna that is excited through I-shaped slots is proposed for applications in sub-6GHz 5G multiple-input-multiple-output (MIMO) antenna systems. The antenna consists of two pairs of folded radiation petals whose base is embedded in a double layer of FR-4 substrate with a common ground-plane which is sandwiched between the two substrate layers. The ground-plane is defected with two I-shaped slots located under the radiation elements. Each pair of radiation elements are excited through a microstrip line on the top layer with RF signal that is 180° out of phase with respect to each other. The RF signal is coupled to the pair of feedlines on the top layer through the I-shaped slots from the two microstrip feedlines on the underside of the second substrate. The proposed feed mechanism gets rid of the otherwise bulky balun. The Bowtie antenna is a compact solution with dimensions of 32×32×33.8 mm3. Measured results have verified that the antenna operates over a frequency range of 3.1–5 GHz and exhibits an average gain and antenna efficiency in the vertical and horizontal polarizations of 7.5 dBi and 82.6%, respectively.
TL;DR: A small-sized antenna for integration with an LCP, which can be operated in the industrial, scientific, and medical (ISM) band of 2.4 GHz, is developed in a spiral shape to provide superior miniaturization, less sensitivity to body tissue variation, and low specific absorption rate (SAR) values, and avoid fabrication complexities due to its small size.
Abstract: Advancement in the technology of leadless cardiac pacemakers (LCPs) has led to ultracompact designs of implantable antennas. In this study, a small-sized antenna for integration with an LCP, which can be operated in the industrial, scientific, and medical (ISM) band of 2.4 GHz, is developed. The proposed antenna was constructed in a spiral shape to provide superior miniaturization, less sensitivity to body tissue variation, and low specific absorption rate (SAR) values, and avoid fabrication complexities due to its small size. The antenna with a footprint of $3 \times 4\,\,\times0.5$ mm3 was constructed on a high dielectric material, namely, Rogers RT/duroid 6010. To the best of the authors’ knowledge, this is the smallest footprint with enhanced performance when compared to previous reports related to implantable antennas. In addition, the antenna was integrated with a 3-D printed LCP having dummy electronics and experimentally validated in saline solution and minced pork. The antenna sustained good impedance matching at the ISM band with a measured bandwidth of 21.88% and 15.46% with the device and without the device, respectively. Due to the smooth electric field (surface currents) over the patch, the antenna system had 270.28 and 31.04 W/kg peak SAR for 1 and 10 g of tissues, respectively, with a maximum peak gain of −25.95 dBi. We also discussed the effects of a coaxial cable and the antenna orientation on its performance. From the measured received signal strength, a stable biotelemetric link can be established between the implant and external controlling device up to a distance of 2 m.
TL;DR: In this article, a planar dual-polarized phased array for 5G cellular communications is proposed, which contains two eight-element subarrays including horizontally polarized end-fire dipole antennas and vertically polarized endfire periodic slot antennas, employed on the PCB ground plane of the 5G mobile platform.
Abstract: A planar dual-polarized phased array is proposed for 5G cellular communications. The array has the properties of dual-polarization, wideband, and quasi-endfire radiation, which is printed on one side of a single-layer substrate. The design contains two eight-element subarrays including horizontally polarized endfire dipole antennas and vertically polarized endfire periodic slot antennas, employed on the PCB ground plane of the 5G mobile platform. Both subarrays provide wide bandwidth to cover 28 and 38 GHz (promising 5G candidate bands). The −10 dB impedance bandwidth of the proposed CPW-fed dipole and slot antennas are 26.5–39.5 GHz and 27.1–45.5 GHz, respectively. Moreover, for −6-dB impedance bandwidth, these values could be more than 20 GHz (24.4–46.4 GHz for the dipole antenna) and 70 GHz (22.3–95 GHz for the slot antenna). The fundamental characteristics of the proposed dual-polarized 5G antenna array in terms of the impedance bandwidth, realized gain, polarization, radiation pattern, and beam steering are investigated and good results are obtained. The clearance of the proposed dual-polarized 5G antenna array is less than 4.5 mm which is sufficient for cellular applications.
TL;DR: In this paper, a dual-polarized and high-gain shared-aperture antenna operating in both the X and Ka bands is proposed. And the shared aperture serves as a phase-shifting surface for the TA antenna and as a partially reflective surface for FP antenna simultaneously.
Abstract: This article describes a dual-polarized and high-gain shared-aperture antenna operating in ${X}$ - and Ka -bands. The proposed shared-aperture antenna is implemented by combining a folded transmitarray (TA) antenna operating in Ka -band and a Fabry–Perot (FP) cavity antenna operating in ${X}$ -band together. In this configuration, the shared aperture serves as a phase-shifting surface for the TA antenna and as a partially reflective surface for the FP antenna simultaneously. Since both of the two antennas radiate into free space through the same physical aperture, the aperture reuse efficiency of the proposed shared-aperture antenna is 100%. A four-layered, metallic double-ring structure is selected as the unit cell (UC) to implement the shared aperture to fulfill the aforementioned requirements. It is found that the frequency responses of the UC in ${X}$ - and Ka -bands are highly independent, which can be controlled separately to facilitate the antenna design and optimization. Two dual-polarized patch antennas operating in ${X}$ - and ${K}\text{a}$ -bands are utilized to enable a dual-polarized manner of the proposed shared-aperture antenna. The simulated results reveal that the proposed shared-aperture antenna has −10 dB bandwidth of 9.8–10.2 GHz and 26.5–29 GHz with the realized gain of 14.8 dBi (at 10 GHz) and 24.4 dBi (at 28 GHz) in two polarizations. All the simulations are experimentally verified.
TL;DR: In this article, a dual-polarized shared-aperture antenna with frequency-selective function for sub-6 GHz base station applications is proposed, where the lower band antenna is designed as a frequency selective surface (FSS) for the nether mid/upper bands (M/UBs) antenna.
Abstract: This article presents a novel triband dual-polarized shared-aperture antenna with frequency-selective function for sub-6 GHz base station applications. The proposed antenna is composed of a dual-polarized square loop antenna with two parasitic loops for 2G/3G/4G (1710–2690 MHz) and a differentially fed dual-polarized planar antenna for 5G (3300–3600 and 4800–5000 MHz) base station applications. These two antennas are placed coaxially but different altitudes for saving the installation space. In order to achieve good individual performance for these two antennas in the same aperture without interference or blocking, the lower band (LB) antenna is designed as a frequency-selective surface (FSS) for the nether mid/upper bands (M/UBs) antenna. The measured results show that the proposed antenna achieves a high port isolation (>20 dB) between LB and M/UBs and a −10-dB impedance bandwidth of 50.4% (1.60–2.70 GHz), 14.9% (3.28–3.80 GHz), and 8.6% (4.75–5.18 GHz). To further validate the design concept, an antenna array composed of four LB elements and eight M/UBs elements with the corresponding spacing is fabricated and measured, which demonstrates the application of the triband shared-aperture antenna in array form.
TL;DR: In this paper, an eight-element linear phased array with frequency selective surface (FSS) operating in the $S$ -band was designed for a wide-angle scanning conformal phased array antenna for an UAV platform.
Abstract: Conformal antennas are practicable candidates to the aerodynamic platforms. A wide-angle scanning conformal phased array antenna for an unmanned aerial vehicle (UAV) platform is designed and presented in this article. An eight-element linear phased array loaded with frequency selective surface (FSS) operating in $S$ -band is investigated. The horizontally polarized antenna element is designed based on a tapered slot feeding dipole. The antenna aperture can be easily conformed to the front wing airframe of the UAV due to the flexibility of the employed polyimide film. To fulfill the requirement of the airborne communication system, two kinds of FSSs are loaded on the dipole antenna to enhance the gain and reduce the 3 dB beamwidth of the main lobe in the elevation plane. To improve the active impedance matching when the beam scans to the large angles, a novel parasitic structure is proposed. Finally, a $1 \times 8$ linear conformal array prototype is simulated, fabricated, and measured. The experimental results indicate that the antenna array achieves a fractional bandwidth of 22.1% with ±70° scanning along the E-plane. The measured results validate the performance of the proposed conformal array and the design.
TL;DR: This antenna is the first dual-band, dual-mode antenna demonstrated on textiles forSWIPT applications and the first matching network-free SWIPT rectenna, demonstrating that SWIPt does not detrimentally affect the energy harvesting or communications performance.
Abstract: This article presents a textile antenna for dual-band simultaneous wireless information and power transfer (SWIPT) The antenna operates as a 24 GHz off-body communications antenna and a sub-1 GHz (785–875 MHz) broad-beam rectenna Incorporated within the broadside microstrip antenna is a high-impedance rectenna for sub-1 GHz power harvesting Utilizing antenna-rectifier co-design, the rectenna eliminates the rectifier matching network The textile antenna is fabricated on a felt substrate and utilizes conductive fabrics for the antenna At 24 GHz, the antenna achieves a realized gain of 72 dBi on a body phantom and a minimum radiation efficiency of 63%, with and without the rectifier The rectenna achieves a best-in-class RF to dc efficiency of 62% from 08 $\mu \text{W}$ /cm2, representing over 25% improvement over state-of-the-art textile rectennas and demonstrating that SWIPT does not detrimentally affect the energy harvesting or communications performance The antenna/rectenna occupies an electrically small area of $0213\times 019\,\,\lambda ^{2}_{0}$ This antenna is the first dual-band, dual-mode antenna demonstrated on textiles for SWIPT applications and the first dual-band matching network-free SWIPT rectenna
TL;DR: In this paper, a low-profile decoupling structure originated from the phase shift concept for the patch antenna array is proposed, which is composed of a half-wave microstrip line and a shorting pin.
Abstract: In this article, a new low-profile decoupling structure originated from the phase shift concept for the patch antenna array is proposed. To clearly illustrate the operation principle, the phase of the signal transmitted from Patch 1 to Patch 2 has been initially studied and the decoupling condition for two closely spaced patch antennas in H-plane has also been obtained. Afterward, the decoupling element concisely composed of a half-wave microstrip line and a shorting pin is developed. Attributing to the introduction of additional signal path by the new decoupling structure, mutual coupling between two adjacent patches is effectively suppressed. To verify the feasibility of the proposed design scheme, demonstrators of two-element patch antennas with and without decoupling structure are, respectively, implemented and analyzed. Results indicate that compared with the coupled array, the isolation between two patch elements is enhanced from 7 to 18 dB at the center frequency of 3.16 GHz under the edge-to-edge separation of only 0.027 $\lambda _{0}$ . Besides, owing to the single layer layout, the profile of the whole antenna structure is as low as 0.02 $\lambda _{0}$ . Ultimately, the proposed decoupling scheme has been applied to the three-element counterpart, so as to demonstrate and validate its effeteness of isolation enhancement for multielement patch array.
TL;DR: A generative machine learning (ML)-based approach is proposed to solve this one-to-many mapping and automate the inverse design of dual- and triple-layer metasurfaces and solve multiobjective optimization problems by synthesizing thin structures composed of potentially brand-new scatterer designs.
Abstract: The synthesis of a metasurface exhibiting a specific set of desired scattering properties is a time-consuming and resource-demanding process, which conventionally relies on many cycles of full-wave simulations. It requires an experienced designer to choose the number of metallic layers, the scatterer shapes and dimensions, and the type and the thickness of the separating substrates. In this article, we propose a generative machine learning (ML)-based approach to solve this one-to-many mapping and automate the inverse design of dual- and triple-layer metasurfaces. Using this approach, it is possible to solve optimization problems with single or more constraints by synthesizing thin structures composed of potentially brand-new scatterer designs, in cases where the interlayer coupling between the layers is nonnegligible and synthesis by traditional methods becomes cumbersome. Various examples to provide specific magnitude and phase responses of $x$ - and $y$ -polarized scattering coefficients across a frequency range as well as bounded responses for different metasurface applications are presented to verify the practicality of the proposed method.