Showing papers in "IEEE Transactions on Antennas and Propagation in 2020"
TL;DR: The fundamental physical phenomena occurring in spacetime systems, such as frequency transitions, nonreciprocity, Fizeau dragging, bianisotropy transformation, and superluminality, allowed when the medium moves perpendicularly to the direction of the wave are described.
Abstract: This article deals with the general concepts underpinning spacetime metamaterials and related systems. It first introduces spacetime metamaterials as a generalization of (bianisotropic) metamaterials, presented in the holistic perspective of direct and inverse spacetime scattering, where spacetime variance and dispersion offer unprecedented medium diversity despite some limitations related to the uncertainty principle. Then, it describes the fundamental physical phenomena occurring in spacetime systems, such as frequency transitions, nonreciprocity, Fizeau dragging, bianisotropy transformation, and superluminality, allowed when the medium moves perpendicularly to the direction of the wave. Next, it extends some principles and tools of relativity physics, particularly a medium-extended version of the spacetime (or Minkowski) diagrams, elaborates a general strategy to compute the fields scattered by spacetime media, and presents a gallery of possible spacetime media, including the spacetime step discontinuity, which constitutes the building brick of any spacetime metamaterial. Finally, the conclusion section provides a list of 16 items that concisely summarizes the key results and teachings of the overall document. The second part establishes the theory and overviews some current and potential applications of spacetime metamaterials.
223 citations
TL;DR: In this article, a metasurface-based decoupling method was proposed to reduce the mutual couplings at two independent bands of two coupled multiple-input-multiple-output (MIMO) antennas.
Abstract: In this communication, a metasurface-based decoupling method (MDM) is proposed to reduce the mutual couplings at two independent bands of two coupled multiple-input-multiple-output (MIMO) antennas. The metasurface superstrate is composed of pairs of non-uniform cut wires with two different lengths. It is compact in size and effective in decoupling two nearby dual-band patch antennas that are strongly coupled in the H-plane with the edge-to-edge spacing of only 0.008 wavelength at low-frequency band (LB). The antenna is fabricated and measured and the results show that the isolation between two dual-band antennas can be improved to more than 25 dB at both 2.5–2.7 GHz and 3.4–3.6 GHz bands, while their reflection coefficients remain to be below −10 dB after the metasurface superstrate is introduced. Moreover, the total efficiency is improved by about 15% in the low band and the envelope correlation coefficient (ECC) between the two antennas is reduced from 0.46 to 0.08 at 2.6 GHz and 0.08 to 0.01 at 3.5 GHz. The proposed method can find plenty of applications in dual-band MIMO and 5G communication systems.
211 citations
TL;DR: In this article, the authors present a vision of the emerging field of spacetime metamaterials, and related systems, in a cohesive and pedagogical perspective, systematically building up the physics, modeling, and applications of these media upon the foundation of their pure-space and pure-time counterparts.
Abstract: The overall article presents the authors’ vision of the emerging field of spacetime metamaterials, and related systems, in a cohesive and pedagogical perspective, systematically building up the physics, modeling, and applications of these media upon the foundation of their pure-space and pure-time counterparts. Following the first part, dealing with the general concepts underpinning spacetime metamaterials, this part establishes the theory of spacetime metamaterials and overviews some of their current and potential applications. It first describes the scattering phenomenology of a spacetime interface, the building brick of any spacetime metamaterial, and deduces the corresponding electromagnetic boundary conditions. Upon this basis, it derives the spacetime interface scattering (Fresnel-like) coefficients and frequency transitions, and subsequently generalizes time reversal to spacetime compansion (compression and expansion). Then, it illustrates the new physics of spacetime metamaterials with the examples of spacetime mirrors and cavities, the inverse prism and chromatic birefringence, and spacetime crystals. Next, it discusses various applications—categorized as frequency multiplication and mixing, matching and filtering, nonreciprocity and absorption, cloaking, electromagnetic processing, and radiation. Finally, the conclusion section provides a list of eight items that concisely summarizes the key results of this article, in completion to the list related to the general concepts in Part I.
168 citations
TL;DR: In this article, a wideband orthogonal-mode dual-antenna pair with a shared radiator for 5G MIMO metal-rimmed smartphones is presented, which shows a wide impedance bandwidth of 3.3-5.0 GHz and a high isolation of more than 21.0 dB across the entire band without using any external decoupling structures.
Abstract: This article presents a wideband orthogonal-mode dual-antenna pair with a shared radiator for fifth-generation (5G) multiple-input multiple-output (MIMO) metal-rimmed smartphones. The wideband decoupling property of the dual-antenna pair is realized by the combination of the orthogonal monopole/dipole modes in the lower band and the orthogonal slot/open-slot modes in the higher band. With the orthogonal-mode design scheme, the dual-antenna pair shows a wide impedance bandwidth of 3.3–5.0 GHz and a high isolation of more than 21.0 dB across the entire band without using any external decoupling structures. By arranging four such dual-antenna pairs at two side edges of the smartphone, an $8 \times 8$ MIMO system is fulfilled. Both the simulation and measurement results show that the proposed $8 \times 8$ MIMO system could offer an isolation of better than 12.0 dB and an envelope correlation coefficient of lower than 0.11 between all ports. The measured average antenna efficiencies are 74.7% and 57.8% for the two antenna elements of the dual-antenna pair. We portend that the proposed design scheme, with merits of shared radiator, wide bandwidth, and metal rim compatibility, has the potential for the application of future 5G smartphones.
152 citations
TL;DR: A novel self-decoupled multiple-input multiple-output (MIMO) antenna pair with a shared radiator with promising potential for the future highly integrated MIMO antennas for 5G smartphones is proposed.
Abstract: In this article, a novel self-decoupled multiple-input multiple-output (MIMO) antenna pair with a shared radiator is proposed for fifth-generation (5G) smartphones. In our approach, a radiator is directly excited by two feeding ports, and interestingly, the two ports are naturally isolated across a wide bandwidth without using any extra decoupling structures. To offer a deep physical insight of the self-decoupling mechanism, a mode-cancellation method based on the synthesis of common and differential modes is developed for the first time. The proposed self-decoupled antenna pair shows a good isolation of better than 11.5 dB across the 5G N77 band (3.3–4.2 GHz) with a radiation pattern diversity property. Based on the self-decoupled antenna pair, an $8 \times 8$ MIMO antenna system, constituted by four sets of antenna pairs, is simulated, fabricated, and measured to validate the concept. The experimental results demonstrate that the proposed $8 \times 8$ MIMO system can offer an isolation of better than 10.5 dB between all ports and a high total efficiency of 63.1%–85.1% across 3.3–4.2 GHz. With the advantages of self-decoupling, shared radiator, simple structure, wide bandwidth, and high efficiency, the proposed design scheme exhibits promising potential for the future highly integrated MIMO antennas for 5G smartphones.
137 citations
TL;DR: It is argued that metamaterial antennas are a near ideal platform for implementing schemes at microwave frequencies and the tradeoffs governing the design and operation of each architecture are examined.
Abstract: This article covers recent advances in the fusion of metasurface antenna design and computational imaging (CI) concepts for the realization of imaging systems that are planar, fast, and low cost. We start by explaining the operation of metamaterial antennas which can generate diverse radiation patterns. Their advantages and distinctions from previous antennas are elucidated. We then provide an intuitive overview of the CI framework and argue that metamaterial antennas are a near ideal platform for implementing such schemes at microwave frequencies. We describe two metamaterial antenna implementations: frequency diverse and electronically reconfigurable. The tradeoffs governing the design and operation of each architecture are examined. We conclude by examining the outlook of metamaterial antennas for microwave imaging and propose various future directions.
126 citations
TL;DR: By carefully designing the regulation voltages applied to the diodes on TDCM, arbitrary constellation diagrams are successfully synthesized and the novel systems can implement various modulation schemes such as quadrature phase shift keying (QPSK), 8PSK, and 16QAM with good communication quality, high stability, and free scheme switching.
Abstract: Metasurfaces are well-designed artificial periodic or quasiperiodic structures to achieve customized electromagnetic responses. Based on the time-domain digital coding metasurface (TDCM) with dynamic reflection or transmission characteristics, one can realize direct information modulation on the metasurface, which has been used in wireless communications. In comparison with the classical architectures of wireless communication systems, the TDCM has advantages for simple architecture, easy manufacture, and low cost. However, the wireless communication systems based on the TDCM are still limited by low conversion efficiency, spectrum pollution, and hard to implement high-order modulation schemes. To solve these limitations, we propose a new route to achieve multi-modulation schemes in wireless communications by regulating the reflection phases of the TDCM in a nonlinear way. By carefully designing the regulation voltages applied to the diodes on TDCM, arbitrary constellation diagrams are successfully synthesized. The novel systems can implement various modulation schemes such as quadrature phase shift keying (QPSK), 8PSK, and 16QAM with good communication quality, high stability, and free scheme switching. The presented method may find important applications in modern wireless communication technologies.
115 citations
TL;DR: In this paper, a dual-band dual-polarized filtering antenna with high selectivity is proposed, where four slots at each side of a square radiating patch are etched with a microstrip line with open-circuit stepped-impedance resonators (OCSIRs).
Abstract: In this communication, a novel dual-band dual-polarized filtering antenna with high selectivity is proposed. By etching four slots at each side of a square radiating patch, dual operation bands as well as a natural radiation null between the two bands are observed. Another two radiation nulls are generated by introducing a novel feeding structure, which is composed of a microstrip line with open-circuit stepped-impedance resonators (OCSIRs). Thus, a dual-band bandpass filtering response of the realized gain is obtained. Each polarization of the antenna is differentially fed, and the differential port isolation is better than 37 dB. A prototype of the antenna element and a $1\times 4$ array is fabricated and tested to validate our design. Measured results show that the antenna element has dual operation bands of 3.28–3.71 and 4.8–5.18 GHz for VSWR < 1.5. Besides, a high out-of-band gain-suppression level which reaches 17.7 dB is also obtained. Good performance of the proposed antenna makes it a promising candidate for 5G sub-6 GHz base station systems.
113 citations
TL;DR: The development of metasurface has always been closely related to antennas, and most fundamental theories of metamurfaces are directly borrowed from antenna array theories; on the other hand, the development of antennas was flourished and expedited by progresses in metasura.
Abstract: Metasurfaces, composed of 2-D planar arrays of sub-wavelength metallic or dielectric scatterers, have provided unprecedented freedoms in manipulating electromagnetic (EM) waves upon interfaces. The development of metasurface has always been closely related to antennas. On the one hand, metasurface was developed from reflect arrays/transmit arrays that are used as reflectors/lens of antennas, and most fundamental theories of metasurfaces are directly borrowed from antenna array theories; on the other hand, the development of antennas was flourished and expedited by progresses in metasurfaces. Many emerging antenna configurations have been constructed based on unique functional metasurfaces. In this article, we will review briefly the development roadmap of both metasurfaces and metasurface-based antennas, including antenna-inspired metasurfaces, metasurface-assisted antennas, and metasurface antennas. In particular, the recent fusion of metasurface and antenna as metantenna will bring significant impacts on methodologies of functional metasurface, antenna design, and radio-frequency device miniaturization.
109 citations
TL;DR: In this article, a transparent, time-modulated metasurface, which functions as a serrodyne frequency translator, is reported at $X$ -band frequencies.
Abstract: Temporally modulated metamaterials have attracted significant attention recently due to their nonreciprocal and frequency converting properties. Here, a transparent, time-modulated metasurface, which functions as a serrodyne frequency translator, is reported at $X$ -band frequencies. With a simple biasing architecture, the metasurface provides electrically tunable transmission phase that covers 360°. A sawtooth waveform is used to modulate the metasurface, allowing Doppler-like frequency translation. Modal analysis of an analogous time-modulated medium is performed to gain insight into the operation of the metasurface-based serrodyne frequency translator. Two such metasurfaces can be cascaded together to achieve magnetless devices that perform either phase or amplitude nonreciprocity.
104 citations
TL;DR: In this paper, a slot-array defected ground structure (DGS) is proposed for decoupling microstrip antenna array, which has the spatial bandstop characteristic and changes the direction of the partially coupled current, respectively.
Abstract: In this article, a novel slot-array defected ground structure (DGS) for decoupling microstrip antenna array is proposed. The slot-array DGS is etched surrounding each antenna element on the ground plane and parallel to the radiating edges of each antenna element. The decoupling mechanism is elucidated via an equivalent circuit model and the coupled current field analysis, which reveals slot-array DGS has the spatial band-stop characteristic and changes the direction of the partially coupled current, respectively. Both characteristics of the slot-array DGS contribute to mutual coupling reduction. Three practical design examples of applying slot-array DGS to single-linearly polarized (LP), dual-LP, and compact circularly polarized (CP) antenna array are given to illustrate the design process and considerations. The simulated and measured results show that about 50 dB isolation enhancement is obtained by using the slot-array DGS when the edge-to-edge spacing between CP antenna elements is 0.057 wavelength. Additionally, a wheel-shaped absorber based on the electromagnetic loss material is designed and fabricated to reduce the backward radiation caused by slot-array DGS. The absorber has an absorptivity of more than 95% in the frequency range of 1.2–1.35 GHz and suppresses the backward radiation over 12.5 dB in the plane phi = 0° and 16.1 dB in the plane phi = 90° without deteriorating other antenna performances.
TL;DR: In this article, a tri-band shared-aperture antenna operating at 2.4, 5.2, and 60 GHz was designed and realized by using the structure-reused technology, and the SIW antenna for the Wi-Gig application can share the same radiator without adding an extra aperture area.
Abstract: This article presents the design and the realization of a tri-band shared-aperture antenna operating at 2.4, 5.2, and 60 GHz. It puts these three bands of antennas within the same radiating aperture and then realizes the Wi-Fi application with MIMO function and the Wi-Gig application with beam-scanning function simultaneously. It consists of two dual-band printed inverted-F antennas (PIFAs) and two SIW leaky wave antennas. By using the structure-reused technology, PIFA for the Wi-Fi application and the SIW antenna for the Wi-Gig application can share the same radiator without adding an extra aperture area. Thus, the ratio of the radiating aperture utilization can be improved greatly. In addition, MIMO technology is also applied to the Wi-Fi antenna design. The envelope correlation coefficients (ECCs) calculated from the simulated and measured data are all lower than 0.04. The measured radiation efficiencies are 74% to 95% and 76% to 95% within these two bands, respectively. Moreover, due to the optimal layout of the whole design, the Wi-Gig antenna can obtain high gain and wide range of beam coverage at the same time. The measured peak gain is 12.29 dBi, and the beam coverage is ±36° from 57 to 64 GHz.
TL;DR: In this article, a double-layered Huygens unit cell is proposed to design a broadband metasurface lens (meta-lens) for 5G millimeter-wave antennas.
Abstract: A double-layered Huygens’ unit cell is proposed to design a broadband metasurface lens (meta-lens) for 5G millimeter-wave antennas. The Huygens’ unit cell consists of a pair of antisymmetric conducting semicircle arc elements on both surfaces of a thin dielectric substrate. The surface currents flowing at the opposite directions on both conducting elements form an electric current loop to induce the orthogonal magnetic current, and then the Huygens’ resonances are stimulated. The Huygens’ unit cell provides the transmission phase coverage of over 400° with transmission amplitude better than −2.3 dB. This breaks through the phase shift limitation of a conventional double-layer frequency-selective surface (FSS) element. It shows that induced magnetism makes such a Huygens-based meta-lens very compact with only one printed circuit board. As an example, a double-layered meta-lens on a 1.5 mm-thick dielectric substrate is designed and experimentally verified. The meta-lens antenna achieves the measured peak gain of 30.7 dBi at 26.2 GHz with an aperture efficiency of 42.25% over the 3 dB bandwidth of 15.7% from 24.1 to 28.2 GHz, fully covering the proposed 5G spectrum from 24.25 to 27.5 GHz. This proposed method greatly helps in the application of promoting planar lightweight low-cost broadband lens antennas in the coming 5G systems.
TL;DR: In this paper, a shared-surface dual-band antenna using characteristic mode analysis (CMA) is proposed for 5G operation using a metasurface at the S$ -band and a partially reflective surface (PRS) at the Ka-band.
Abstract: A shared-surface dual-band antenna is proposed for 5G operation using characteristic mode analysis (CMA). The surface is the integration of a metasurface at the ${S}$ -band and a partially reflective surface (PRS) at the Ka -band. The resonant mode of the metasurface is excited by a microstrip-fed slot, and the PRS with a pair of substrate-integrated waveguide (SIW)-fed slots are employed to form a Fabry–Perot resonator antenna (FPRA). Measurements realized on a physical prototype of the antenna show a 10 dB impedance bandwidth of 23.45% and 9.76% and a realized gain that varies from 7.27 to 10.44 dBi and from 11.8 to 14.6 dBi, over the ${S}$ -band (3.2–4.05 GHz) and the Ka -band (26.8–29.55 GHz), respectively.
TL;DR: In this article, the authors proposed a time-modulated reflective metasurface that causes a frequency shift to the impinging radiation, thus realizing an artificial Doppler effect in a nonmoving electrically thin structure.
Abstract: Metasurfaces consisting of electrically thin and densely packed planar arrays of subwavelength elements enable an unprecedented control of the impinging electromagnetic fields. Spatially modulated metasurfaces can efficiently tailor the spatial distribution of these fields with great flexibility. Similarly, time-modulated metasurfaces can be successfully used to manipulate the frequency content and time variations in the impinging field. In this article, we present time-modulated reflective metasurfaces that cause a frequency shift to the impinging radiation, thus realizing an artificial Doppler effect in a nonmoving electrically thin structure. Starting from the theoretical analysis, we analytically derive the required time modulation of the surface admittance to achieve this effect and present a realistic time-varying structure, based on a properly designed and dynamically tuned high-impedance surface. It is analytically and numerically demonstrated that the field emerging from the metasurface is up-/down-converted in frequency according to the modulation profile of the metasurface. The proposed metasurface concept, enabling a frequency modulation of the electromagnetic field “on-the-fly,” may find application in telecommunication, radar, and sensing scenarios.
TL;DR: In this article, a dual-polarized millimeter-wave (mm-wave) patch antenna with bandpass filtering response is proposed, which consists of a differential-fed cross-shaped driven patch and four stacked parasitic patches.
Abstract: This article presents a novel dual-polarized millimeter-wave (mm-Wave) patch antenna with bandpass filtering response. The proposed antenna consists of a differential-fed cross-shaped driven patch and four stacked parasitic patches. The combination of the stacked patches and the driven patch can be equivalent to a bandstop filtering circuit for generating a radiation null at the upper band edge. Besides, four additional shorted patches are added beside the cross-shaped driven patch to introduce another radiation null at the lower band edge. Moreover, by embedding a cross-shaped strip between these four stacked patches, the third radiation null is generated to further suppress the upper stopband. As a result, a quasi-elliptic bandpass response is realized without requiring extra filtering circuit. For demonstration, a prototype was fabricated with standard PCB process and measured. The prototype operates in the 5G band (24.25–29.5 GHz) and it has an impedance bandwidth of 20%. The out-of-band gain drops over 15 dB at 23 and 32.5 GHz, respectively, which exhibits high selectivity. These merits make the proposed antenna a good element candidate for the 5G mm-Wave massive MIMO applications to reduce the requirements of the filters in the mm-Wave RF front ends.
TL;DR: In this article, a ray-tracing model is used to evaluate the phase distribution in the aperture of a geodesic lens with respect to the relative permittivity distribution of axially symmetric surfaces.
Abstract: This article describes a design procedure that enables a time-efficient evaluation of the focusing properties of modulated geodesic lenses using ray tracing on the equivalent gradient-index planar lens. The method uses transformation optics to define the equivalent planar relative permittivity distribution of axially symmetric surfaces and a ray-tracing model to evaluate the phase distribution in the aperture of the lens. This approach is of interest to optimize modulated geodesic lenses having polynomial profiles, reducing their height while preserving their wideband behavior and wide angular focusing properties. The approach is validated with a specific lens design. The profile is optimized at 30 GHz, while the focusing properties are monitored over the complete Ka up-link frequency band allocated to satellite communications (i.e., 27.5–31 GHz). The manufactured prototype produces 21 beams equally spaced every 7.5° over the extended angular range of ±75°. The ray-tracing model results are compared in detail with the corresponding full-wave model results and experimental data. The manufactured design has return loss better than 15 dB over a fractional frequency bandwidth larger than 30%, in line with the predictions. Excellent scanning properties are demonstrated over an angular range of ±60° with scan losses below 1 dB and good pattern stability, including on sidelobe levels. A height reduction by a factor of 4, when compared to a conventional geodesic lens, is demonstrated with this specific design.
TL;DR: Flexible and lightweight textile-integrated rectenna arrays for powering wearable electronic devices and several tests are presented to demonstrate the proposed system’s applicability for charging and powering low-power wearable electronics devices.
Abstract: In this article, we demonstrate flexible and lightweight textile-integrated rectenna arrays for powering wearable electronic devices. We propose a method to exploit large clothing-areas to integrate arrays consisting of $2\times2$ and $2\times3$ rectenna elements. Each element comprises a patch antenna and a rectifier which are fabricated using embroidery of conductive thread on the textile substrates. The rectifier used single-diode circuit configuration and showed a radio frequency (RF)-to-dc conversion efficiency of 70% for an applied input RF-power of 8 dBm at its input port. We also present several tests to demonstrate the applicability of the rectenna array. Specifically, in boosted-Wi-Fi modality, a dc power of $600~\mu \text{W}$ was collected at 10 cm from the source and $80~\mu \text{W}$ was collected at 60 cm from the source. These demonstrations show the proposed system’s applicability for charging and powering low-power wearable electronic devices.
TL;DR: A new self-decoupling method, namely weak-field-based decoupling technique, is proposed and validated based on inset-fed patch antenna arrays, which is very promising for MIMO applications.
Abstract: In this article, a new self-decoupling method, namely weak-field-based decoupling technique, is proposed and validated based on inset-fed patch antenna arrays. The self-decoupling effect is realized by taking advantage of the inherent weak-field area created by the feeding structure and proposed inset-fed patch. By strategically arranging the array element in the weak-field area of the adjacent antenna element, the coupling strength between adjacent elements can be controlled under a very low level without the need of any additional decoupling circuitry or structures. A two-element patch antenna array was first developed and analyzed, achieving a peak isolation level of 61 dB. Afterward, a four-element linear patch antenna array was designed, fabricated, and measured to further validate the proposed technique. With the distinct advantages of simple structure and effective isolation enhancement, the proposed self-decoupling method is very promising for MIMO applications.
TL;DR: In this paper, a flexible high-permittivity dielectric substrate is developed using silicon-based poly-di-methyl-siloxane (PDMS) matrix and microscale of aluminium oxide (Al2O3) and graphite (G) powders.
Abstract: An approach toward designing and building of a compact, low-profile, wideband, unidirectional, and conformal imaging antenna for electromagnetic (EM) head imaging systems is presented. The approach includes the realization of a custom-made flexible high-permittivity dielectric substrate to achieve a compact sensing antenna. The developed composite substrate is built using silicon-based poly-di-methyl-siloxane (PDMS) matrix and microscale of aluminium oxide (Al2O3) and graphite (G) powders. Al2O3 and G powders are used as fillers with different weight-ratio to manipulate and control the dielectric properties of the substrate for attaining better matched with the human head and reducing antenna’s physical size while keeping the PDMS flexibility feature. Using the custom-made substrate, a compact, wideband, and unidirectional on-body matched antenna for wearable EM head imaging system is realized. The antenna is configured as a multi-slot planar structure with four shorting pins, working as electric and magnetic dipoles at different frequency bands. The measured reflection coefficient (S11) shows an operating frequency band of 1–4.3 GHz. The time-average power density and the amplitude of the received signal inside the MRI-based realistic head phantom demonstrate a unidirectional propagation and high-fidelity factor (FF) of more than 90%. An array of 13 antennas are fabricated and tested on a realistic 3-D head phantom to verify the imaging capability of the proposed antenna. The reconstructed images of different targets inside the head phantom demonstrate the possibility of utilizing the conformal antenna arrays to detect and locate abnormality inside the brain using multistatic delay-multiply-and-sum beamforming algorithm.
TL;DR: The automated techniques are shown to provide an efficient, flexible, and reliable framework to identify optimal design parameters for a reference dual-band double T-shaped monopole antenna to achieve favorite performance in terms of its two bands.
Abstract: In this communication, we propose using modern machine learning (ML) techniques including least absolute shrinkage and selection operator (lasso), artificial neural networks (ANNs), and $k$ -nearest neighbor (kNN) methods for antenna design optimization. The automated techniques are shown to provide an efficient, flexible, and reliable framework to identify optimal design parameters for a reference dual-band double T-shaped monopole antenna to achieve favorite performance in terms of its two bands, i.e., between 2.4 and 3.0 and 5.15 and 5.6 GHz. In this communication, we also present a thorough study and comparative analysis of the results predicted by these ML techniques, with the results obtained from high-frequency structure simulator (HFSS) to verify the accuracy of these techniques.
TL;DR: This time-varying coding strategy provides a new way to design higher bit programmable metasurface and simplify the structural design and control system, which will find many potential applications such as high-resolution imaging and high-capacity wireless communications.
Abstract: Recently, digital coding metasurfaces have attracted significant attention due to their capability to dynamically control electromagnetic waves in programmable ways. When the digital bit of a metasurface is higher, its controlling capability will be stronger. However, it is extremely difficult to realize 3-bit and higher digital coding metasurfaces since an $n$ -bit digital element will require many active devices (e.g., p-i-n diodes) to achieve $2^{n}$ digital states. Here, we propose to realize arbitrary multi-bit programmable phases using 2-bit time-domain digital coding metasurface at the central frequency or harmonic frequencies. We introduce the method of vector synthesis to design the phase coverages, from which 4-bit and arbitrarily higher-bit coding phases are synthesized by a physical coding metasurface with only 2-bit phases, simply by manipulating the time-coding sequences. A prototype controlled by a field-programmable gate array is used to validate this methodology. The experimental results are in good agreement with the theoretical analysis, which demonstrate good performance of the proposed method in dynamically realizing arbitrary multi-bit programmable phases. This time-varying coding strategy provides a new way to design higher bit programmable metasurface and simplify the structural design and control system, which will find many potential applications such as high-resolution imaging and high-capacity wireless communications.
TL;DR: In this paper, wave attenuation through rain with different rainfall rates at millimeter wave and low-terahertz (Low-THz) ( $f = 300$ GHz) frequencies is studied.
Abstract: Wave attenuation through rain with different rainfall rates at millimeter wave ( $f = 77$ GHz) and low-terahertz (Low-THz) ( $f = 300$ GHz) frequencies is studied in this article. Rain has pronounced impacts on electromagnetic wave propagation and one of the well-known effects is attenuation of the transmitted wave. Attenuation at both frequencies and hydrometeor properties [rainfall rate and drop size distribution (DSD)] are measured simultaneously. The measured DSD is fit with gamma and Weibull distributions and is also compared to the frequently used distribution Marshall and Palmer (MP) model; Weibull is shown to be a better fit to the measured DSDs. Theoretical prediction of attenuation as a function of rainfall rate (up to about 20 mm/h) is determined using Mie scattering theory, and the fit gamma and Weibull, and MP distribution models; as well as using the International Telecommunications Union Radiocommunication Sector (ITU-R) recommendation. The calculations are evaluated by comparing them to the experiment. The measured results at 77 GHz best agree with the ITU-R recommendation whereas at 300 GHz, the calculation based on Mie scattering and the Weibull distribution exhibits the best fit to the measured data. The measured data that exceed the theoretical prediction are analyzed and interpreted based on their corresponding observed drop size properties, for the first time.
TL;DR: A learning-based inversion approach in the frame of the U-net convolutional neural network to quantitatively image unknown scatterers located in homogeneous background from the amplitude-only measured total field is proposed and found that the proposed PD-CSI and PD-DICs perform better in terms of accuracy, generalization ability, and robustness compared with DIS.
Abstract: Without phase information of the measured field data, the phaseless data inverse scattering problems (PD-ISPs) counter more serious nonlinearity and ill-posedness compared with full data ISPs (FD-ISPs). In this article, we propose a learning-based inversion approach in the frame of the U-net convolutional neural network (CNN) to quantitatively image unknown scatterers located in homogeneous background from the amplitude-only measured total field (also denoted PD). Three training schemes with different inputs to the U-net CNN are proposed and compared, i.e., the direct inversion scheme (DIS) with phaseless total field data, retrieval dominant induced currents by the Levenberg–Marquardt (LM) method (PD-DICs), and PD with contrast source inversion (PD-CSI) scheme. We also demonstrate the setup of training data and compare the performance of the three schemes using both numerical and experimental tests. It is found that the proposed PD-CSI and PD-DICs perform better in terms of accuracy, generalization ability, and robustness compared with DIS. PD-CSI has the strongest capability to tackle with PD-ISPs, which outperforms the PD-DICs and DIS.
TL;DR: In this article, a planar lens antenna with the size of $10 ε ε + ε − ε is proposed and characterized for full-dimensional massive MIMO and multibeam systems at sub-6 GHz bands.
Abstract: A metasurface lens antenna fed by a planar $8\times8$ dual polarized antenna array is proposed and characterized for full-dimensional massive multiple-input multiple-output (MIMO) and multibeam systems at sub-6 GHz bands. The lightweight multilayer metasurface structure consisting of Jerusalem cross elements is used for a planar lens design. The lens antenna with the size of $10\lambda _{0} \times 10\lambda _{0} \times 5\lambda _{0}$ is fed by an $8\times8$ dual-polarized stacked patch array to operate over the range from 5.17 to 6.10 GHz, where $\lambda _{0}$ is the free-space operating wavelength at the center frequency of 5.6 GHz. This article shows the scanning range of ±25° with a maximum gain of 22.4 dBi and the gain variation of 3.3 dB at 5.6 GHz. Beam coverage performance, pattern envelope correlation coefficient, and port isolation properties demonstrate its full-dimension access capability of the antenna. Besides, the multibeam antenna system with high-gain coverage is achieved by beams operating at the same frequencies, while the frequency division multiplexing can be realized for the isolated beams. The proposed metasurface lens antenna, featuring lightweight, compactness, and low cost compared to a 3-D dielectric lens and low-complexity compared to the array scenarios, can be an alternative for fifth-generation (5G) sub-6 GHz frequency bands.
TL;DR: An aperture-sharing technique is developed, so that a four-unit linear 28 GHz array and a 3.5 GHz dipole antenna can be integrated and the same aperture can be shared, and the proposed dual-frequency antenna is suitable for some terminal applications in the next-generation wireless networks.
Abstract: The integration of the sub-6 GHz and millimeter-wave (mmWave) antennas has become an important issue for the next-generation wireless communication. For the mmWave band, adaptive beam steering is required to solve the path loss and coverage range problems. In this communication, an aperture-sharing technique is developed, so that a four-unit linear 28 GHz array and a 3.5 GHz dipole antenna can be integrated and the same aperture can be shared. The SIW is utilized to enable the integration and maintain the radiation of both antennas, without mutual interference. By adopting a separate feeding network, each mmWave array unit is independently excited, so that a beam steerable in the E-plane can be synthesized in the mmWave band. A prototype is fabricated with a compact size owing to the shared aperture. The measured results show good radiation characteristics and broad 10 dB impedance bandwidth exceeding 20% in both bands. Furthermore, the mmWave beam steering is obtained with a stable gain level. The proposed dual-frequency antenna is suitable for some terminal applications in the next-generation wireless networks.
TL;DR: In this paper, a hybrid topology of fully metallic spatial phase shifters is developed for the AMPCS, resulting in an extremely lower prototyping cost as that of other state-of-the-art substrate-based PCSs.
Abstract: This article addresses a critical issue, which has been overlooked, in relation to the design of phase-correcting structures (PCSs) for electromagnetic bandgap (EBG) resonator antennas (ERAs). All the previously proposed PCSs for ERAs are made using either several expensive radio frequency (RF) dielectric laminates or thick and heavy dielectric materials, contributing to very high fabrication cost, posing an industrial impediment to the application of ERAs. This article presents a new industrial-friendly generation of PCS, in which dielectrics, known as the main cause of high manufacturing cost, are removed from the PCS configuration, introducing an all-metallic PCS (AMPCS). Unlike existing PCSs, a hybrid topology of fully metallic spatial phase shifters are developed for the AMPCS, resulting in an extremely lower prototyping cost as that of other state-of-the-art substrate-based PCSs. The APMCS was fabricated using laser technology and tested with an ERA to verify its predicted performance. The results show that the phase uniformity of the ERA aperture has been remarkably improved, resulting in 8.4 dB improvement in the peak gain of the antenna and improved sidelobe levels (SLLs). The antenna system including APMCS has a peak gain of 19.42 dB with a 1 dB gain bandwidth of around 6%.
TL;DR: In this paper, a zero-ground-clearance dual antenna pair with high isolation and balanced high performance was proposed, where a T-shaped monopole intersects with a Tshaped slot that is etched on a large ground edge.
Abstract: For the first time, zero-ground-clearance dual antenna pair with high isolation and balanced high performance is proposed. A T-shaped monopole intersects with a T-shaped slot that is etched on a large ground edge, constituting the CPW-fed dual antenna pair. By exploiting the odd and even modes of the CPW structure, two orthogonal characteristic modes including the in-phase current and monopole modes can be excited, generating high port isolation. Both modes are unbalanced mode, which means that the ground currents can be fully excited, so the two antennas are with balanced high performance. A sub-6 GHz antenna pair that occupies a footprint of $15\times 7$ mm2 ( $0.18\,\,\lambda \,\times 0.08\,\,\lambda$ ) is analyzed and the simulated results show an isolation of better than −24 dB and an envelope correlation coefficient (ECC) of lower than 0.0016, −6 dB bandwidths of 230 and 240 MHz, and average efficiencies of 57.9% and 57.4%. A four-antenna multiple-input multiple-output (MIMO) array is fabricated and measured to verify the feasibility. The measured isolations and ECCs of the two modes are, respectively, better than −20.0 dB and 0.04, −6 dB bandwidths are 230 MHz/240 MHz and 220 MHz/230 MHz, and average efficiencies are 54.5%/50.2% and 49.9%/48.6%. The proposed dual antenna pair exhibits a great potential for 5G MIMO smartphone application.
TL;DR: In this paper, a dual-polarized end-fire phased array for 5G handset devices at 28 GHz was proposed, which achieved a −10 dB frequency bandwidth of 5.3% and a −6 dB bandwidth of 25% overlapping between the vertical and horizontal polarization.
Abstract: This communication proposes a dual-polarized end-fire phased array for 5G handset devices at 28 GHz. The proposed four-element array has low profile of 1.1 mm, small clearance of 2.7 mm, and symmetric patterns in the vertical plane. The array element is fed by substrate-integrated waveguide (SIW), which works as a waveguide (WG) antenna with vertically polarized radiation pattern. Two transition plates are introduced to improve the impedance matching of the WG antenna. The horizontal polarization is generated by exciting one of the transition plates as an antenna. The other transition plate is modified as a group of triangle strips to minimize its reflection to the horizontal radiation patterns. A −10 dB frequency bandwidth of 5.3% and a −6 dB bandwidth of 25% are achieved, overlapping between the vertical and horizontal polarization. The array scanning angle is from −54° to 44° at 29 GHz for both polarization. Within the scanning range, the end-fire gain varies from 7.48 to 8.14 dBi for the horizontal polarization, whereas from 4.49 to 8.05 dBi for the vertical polarization. Good agreements between simulations and measurements are well achieved and shown in this communication.
TL;DR: In this paper, a 1-bit reconfigurable transmitarray antenna (RTA) using an equivalent magnetic dipole element for wide-angle beam scanning at Ku-band is presented.
Abstract: A novel 1 bit reconfigurable transmitarray antenna (RTA) using an equivalent magnetic dipole element for wide-angle beam scanning at Ku -band is presented. The RTA element consists of a rectangular patch and a side-shorted patch with an equivalent magnetic dipole radiation. A 1 bit phase difference is achieved by controlling two p-i-n diodes on the side-shorted patch based on the current reversal mechanism. The half-power beamwidth of the presented antenna element is 142° in E-plane, which is significantly larger than other conventional elements. A RTA prototype with $16\times16$ elements is designed, fabricated, and tested. The measured results show good beam scanning capabilities of the 1 bit RTA. The measured gain in the broadside direction is 21.4 dBi, and the scan gain loss is 3.6 dB for the 60° scanned beam in E-plane.