Showing papers in "IEEE Transactions on Antennas and Propagation in 2019"
TL;DR: In this article, the authors exploit a connection between the deep neural network (DNN) architecture and the iterative method of nonlinear EM inverse scattering, and propose DeepNIS, which consists of a cascade of multilayer complex-valued residual convolutional neural network modules.
Abstract: Nonlinear electromagnetic (EM) inverse scattering is a quantitative and super-resolution imaging technique, in which more realistic interactions between the internal structure of scene and EM wavefield are taken into account in the imaging procedure, in contrast to conventional tomography. However, it poses important challenges arising from its intrinsic strong nonlinearity, ill-posedness, and expensive computational costs. To tackle these difficulties, we, for the first time to our best knowledge, exploit a connection between the deep neural network (DNN) architecture and the iterative method of nonlinear EM inverse scattering. This enables the development of a novel DNN-based methodology for nonlinear EM inverse problems (termed here DeepNIS). The proposed DeepNIS consists of a cascade of multilayer complex-valued residual convolutional neural network modules. We numerically and experimentally demonstrate that the DeepNIS outperforms remarkably conventional nonlinear inverse scattering methods in terms of both the image quality and computational time. We show that DeepNIS can learn a general model approximating the underlying EM inverse scattering system. It is expected that the DeepNIS will serve as powerful tool in treating highly nonlinear EM inverse scattering problems over different frequency bands, which are extremely hard and impractical to solve using conventional inverse scattering methods.
278 citations
TL;DR: A novel balanced open-slot antenna is designed as an array antenna element, in which this antenna design can yield a balanced slot mode that can enhance the isolation between two adjacent input ports and further mitigates the coupling between antenna elements.
Abstract: A high-isolation eight-antenna multi-input multi-output (MIMO) array operating in the 3.5 GHz band (3.4–3.6 GHz) for future smartphones is proposed. Here, a novel balanced open-slot antenna is designed as an array antenna element, in which this antenna design can yield a balanced slot mode (with reduced ground effects) that can enhance the isolation between two adjacent input ports. Furthermore, by meticulously arranging the positions of the eight antenna elements, desirable polarization diversity can also be successfully achieved, which further mitigates the coupling between antenna elements. A prototype was manufactured to validate the simulation. A good impedance matching (return loss > 10 dB), high isolation (>17.5 dB), high total efficiency (>62%), and low envelope correlation coefficient (ECC, <0.05) were measured across the desired operation bandwidth. To verify the MIMO performance, ergodic channel capacity using the Kronecker channel model was calculated. The effects of hand phantom were also studied.
201 citations
TL;DR: It is the first time that the contrast source is learned to solve full-wave inverse scattering problems (ISPs) and the proposed induced current learning method (ICLM) is compared with the state-of-the-art of deep learning scheme and a well-known iterative ISP solver.
Abstract: In this paper, to bridge the gap between physical knowledge and learning approaches, we propose an induced current learning method (ICLM) by incorporating merits in traditional iterative algorithms into the architecture of convolutional neural network (CNN). The main contributions of the proposed method are threefold. First, to the best of our knowledge, it is the first time that the contrast source is learned to solve full-wave inverse scattering problems (ISPs). Second, inspired by the basis-expansion strategy in the traditional iterative approach for solving ISPs, a combined loss function with multiple labels is defined in a cascaded end-to-end CNN (CEE-CNN) architecture to decrease the nonlinearity of objective function, where no additional computational cost is introduced in generating extra labels. Third, to accelerate the convergence speed and decrease the difficulties of the learning process, the proposed CEE-CNN is designed to focus on learning the minor part of the induced current by introducing several skip connections and to bypass the major part of induced current to the output layers. The proposed method is compared with the state-of-the-art of deep learning scheme and a well-known iterative ISP solver, where numerical and experimental tests are conducted to verify the proposed ICLM.
163 citations
TL;DR: In this paper, a miniaturized frequency-selective rasorber (FSR) was proposed, which has a wide transmission band with low insertion loss and a wide absorption band below the transmission band.
Abstract: This paper presents a miniaturized frequency-selective rasorber (FSR) that has a wide transmission band with low insertion loss and a wide absorption band below the transmission band. The FSR is composed of a resistive sheet and a bandpass frequency-selective surface (FSS). The unit cell of the resistive sheet is a resistor-loaded hexagonal metallic loop, each side of which is inserted with a circular spiral resonator (CSR) in the center. The CSR is equivalent to a parallel LC circuit that has a high inductance and low parasitic capacitance. At a high frequency of 10 GHz, the CSR resonates to be infinite impedance, around which a 0.5 dB transmission band of 8.68–11.34 GHz is produced. The bandpass FSS is a triple-layer FSS in which two layers of identical hexagonal patches are coupled through a layer of hexagonal aperture; it has a fast rolloff 0.5 dB transmission band of 8.2–11.33 GHz, which almost coincides with that of the resistive sheet. The 1 dB transmission band of the FSR by placing the resistive sheet on the bandpass FSS is 8.3–11.07 GHz. At low frequency, the FSR performs as an absorber, and the 10 dB absorption band is 2.4–7.1 GHz. In addition, due to its tiny physical sizes of only $1.2\,\,\text {mm}\times 1.6$ mm, the CSR can be viewed as a lumped element circuit with a high inductance, in which the parallel resonance is almost independent to the incident angle. The transmission performance of the FSR has a good independence of polarizations and incident angles. A prototype of the proposed FSR is fabricated and measured to validate the design.
144 citations
TL;DR: In this article, a dual-band shared-aperture antenna based on the concept of structure reuse is proposed, which consists of a patch antenna working at 3.5 GHz and a $12 \times 12$ substrate integrated waveguide (SIW) slot array antenna working on 60 GHz.
Abstract: The operating frequency of future communication systems will cover unlicensed millimeter-wave bands as well as existing microwave bands. Large frequency ratio antennas that can be applied to both frequency bands simultaneously and maintain the high isolation between the two channels are difficult to design. This paper presents a new design of dual-band shared-aperture antenna based on the concept of structure reuse. The antenna consists of a patch antenna working at 3.5 GHz and a $12 \times 12$ substrate integrated waveguide (SIW) slot array antenna working at 60 GHz. The frequency ratio of this shared-aperture antenna is 17. In this design, the overall structure of the SIW slot array antenna is employed as the radiator of the patch antenna. With this new scheme, the high aperture reuse efficiency can be achieved. Meanwhile, the millimeter-wave antenna based on the SIW technology has the high-pass nature to reject the lower frequency signal. A compact microstrip resonant cell that acts as a low-pass filter is connected in series on the feedline of the microwave antenna to suppress the upper frequency signal. Thus, the channel isolation between the patch and the SIW slot array antennas can be more than 130 dB at 3.5 GHz and 65 dB at 60 GHz.
141 citations
TL;DR: In this article, a dual-band dual-polarized base station antenna array is developed for 5G applications by introducing a frequency-selective surface (FSS) between radiators operating in the 0.69-0.96 GHz and 3.5-4.9 GHz bands.
Abstract: A dual-band dual-polarized base station antenna array is developed for fifth generation (5G) applications. Low-profile characteristic, high isolations, and shared-aperture are realized by introducing a frequency-selective surface (FSS) between radiators operating in the 0.69–0.96 GHz (B1) and 3.5–4.9 GHz (B2) bands. The dual-polarized B1-band antenna has a low-profile height of $0.12~\lambda _{L}$ ( $\lambda _{L}$ is the wavelength at the center frequency of B1). As for the B2 band, a $2 \times 2$ dual-polarized array sharing the same aperture with the B1-band antenna is developed for the sub-6 GHz band. Severe mutual coupling between B1- and B2-band antennas is reduced by the FSS. High port isolation (> 25 dB) between B1- and B2-band antennas is achieved. A prototype consisting of one B1-band antenna and a $2 \times 2$ B2-band antenna array is fabricated. Measured results show that the proposed dual-band dual-polarized array achieves 32.7% and 33.3% bandwidth in the B1 and B2 bands, respectively. Measured results also demonstrate that the proposed array offers stable radiation patterns, high gains, and high cross-polarization discriminations (XPD > 20 dB) across the two frequency bands. These attractive features make this array an ideal candidate for future 5G massive MIMO base station antenna developments.
137 citations
TL;DR: In this article, a dual-band linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed, which consists of two identical metallic layers with a combination of a connected Jerusalem cross (JC) and an I-type dipole for each layer.
Abstract: A dual-band linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The element of the converter consists of two identical metallic layers with a combination of a connected Jerusalem cross (JC) and an “I”-type dipole for each layer. The proposed converter is designed by using an equivalent circuit model (ECM). Left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) beams can be, respectively, generated at ${K}$ -band and Ka -band excited by a linearly polarized (LP) wave tilted 45° relative to the ${x}$ - and ${y}$ -directions of the converter. In addition, the converter covers two operation bands for ${K}$ -/ Ka -band satellite communications with high conversion efficiency and low polarization extinction ratio (PER). After full-wave optimization, the proposed converter is fabricated and measured. The measured results show a good agreement with the simulated ones. Even though there exists a tradeoff between the angular stability and the bandwidth of the dual-band LCPCs, the measured axial ratio (AR) remains stable in the lower operation band and a slight fluctuation in the higher band with the incident angle of 20°.
135 citations
TL;DR: In this paper, a bilayer subwavelength scatterer was proposed to generate orbital angular momentum (OAM) waves at microwave frequencies with high efficiency, which can be used for the design, fabrication, and characterization of an ultra-thin metasurface.
Abstract: Metasurfaces deployed for generating electromagnetic waves that carry orbital angular momentum (OAM) in the transmission mode are generally inefficient in operation. In this paper, we present a method for the design, fabrication, and characterization of an ultra-thin metasurface which could be used for generating OAM waves at microwave frequencies with high efficiency. We achieve this objective by proposing a novel bilayer subwavelength scatterer having $\pi $ retardation phase between two orthogonal polarizations of an incident circularly polarized (CP) wave that also have high amplitudes. When analyzed our setup using Jones matrices, we find that the scatterer inverts the spin direction of the incident CP wave with high efficiency. Furthermore, the setup provides full phase control with the spatial rotation of the scatterer as per Pancharatnam-Berry Phase Mechanism. To further illustrate the utility of the proposal, a metasurface was designed based on the proposed scatterer and the generation of OAM waves is validated through both simulations and experimental measurements. To further clarify the points, a rigorous analysis for the transmission and conversion efficiencies is presented.
131 citations
TL;DR: In this article, a novel decoupling technique for closely packed patch antennas using near-field resonator (NFR) above each antenna element is proposed, which can be easily applied to multiple-input multiple-output (MIMO) antennas having multiple patch elements.
Abstract: In this paper, a novel decoupling technique for closely packed patch antennas using near-field resonator (NFR) above each antenna element is proposed. The decoupling mechanism is illustrated by investigating the electric-field (E-field) and magnetic-field (H-field) distributions. The E-field distributions indicate that the NFRs above the patches serve as coupling-mode transducers to produce an orthogonal coupling mode at the desired resonance, leading to high port isolation between the patches. The H-field distributions demonstrate that the H-fields in the substrate are confined within the excited element, leading to the effective suppression of antenna mutual coupling. The NFR can be easily applied to multiple-input multiple-output (MIMO) antennas having multiple patch elements. Three practical decoupling examples are demonstrated and the simulation and measurement results show that impedance matching for each antenna port and isolation of better than 20 dB are achieved for all these examples using the NFRs. Moreover, for the H-plane and E-plane decoupling of wideband two-port MIMO antennas, wide decoupled impedance bandwidths of 6.1% and 5.8% are obtained, respectively. More results of radiation patterns reveal that good radiation performance is reserved with no reduction in realized gain or front-to-back ratio.
123 citations
TL;DR: In this paper, a closely located dual-band meander-line antenna array with isolation enhancement by inserting novel split electromagnetic bandgap (EBG) uniplanar structure is proposed.
Abstract: A closely located dual-band meander-line antenna array with isolation enhancement by inserting novel split electromagnetic bandgap (EBG) uniplanar structure is proposed. The meander-line antenna is coupled to a parasitic rectangular patch to achieve the dual-band operation. Splits are applied on the surface of an EBG structure to cause decoupling at the first resonant mode and utilizing an EBG structure to decouple at the second resonant mode. The prototype of the proposed structure achieves a dual band of 180 MHz (3.42–3.6 GHz) and 400 MHz (4.7–5.1 GHz). The mutual coupling is significantly reduced by 26 and 44 dB at 3.48 and 4.88 GHz, respectively, compared to the reference antenna. In addition, the structure has high front-to-back ratio radiation characteristics.
120 citations
TL;DR: Due to the advantages such as multiband operation, MIMO configuration for 5G communications, high isolation, and compact structure, the proposed antenna design is attractive for 4G/5G smartphones.
Abstract: In this paper, multiband antennas based on a single ring slot are proposed for 4G/5G smartphone applications. The basic structure of the antenna is consisted of a large metal ground and an unbroken metal rim, in which a single 2 mm-wide ring slots is realized between the metal ground and rim. Here, a reconfigurable 4G antenna (820–960 and 1710–2690 MHz) is initially devised by loading multiple grounded stubs and a simple dc controlling circuit with varactor diode into the upper section of the ring slot. To further cover the sub-6 GHz spectrum (3400–3600 MHz) for future 5G communications, a four-element multi-input multi-output (MIMO) slot antennas configuration is designed by utilizing the lower section of the ring slot. A prototype antenna was fabricated, and good agreement is shown between the measured and simulated results. Due to the advantages such as multiband operation, MIMO configuration for 5G communications, high isolation, and compact structure, the proposed antenna design is attractive for 4G/5G smartphones.
TL;DR: In this paper, a spatial reuse dual antenna pair consisting of a split on the metallic bezel and a slot on the mainboard ground, where the slot is centered on the split, was proposed for 5G smartphones with metallic bezels.
Abstract: This paper proposes a polarization-orthogonal co-frequency dual antenna pair suitable for fifth-generation (5G) multiple-input multiple-output (MIMO) smartphone with metallic bezels. The proposed spatial-reuse dual antenna pair consists of a split on the metallic bezel and a slot on the mainboard ground, where the slot is centered on the split. Two orthogonal degenerate characteristic modes operating at half wavelength including in-phase current and slot modes can be excited on the same antenna structure. An end-shorted microstrip line that crosses the split is used to excite the in-phase current mode, producing $y$ -polarized radiation, while a symmetrical slot-centered Y-shaped feeding network with its shorted ends crossing the slot is adopted to excite the slot mode, producing $x$ -polarized radiation. To the best of authors’ knowledge, this is the first time that a co-frequency dual antenna pair suitable for smartphone with metallic bezels is proposed. A sub-6 GHz dual antenna pair operating at 3.5 GHz that occupies a footprint of $25 \times 7 \times 1.5$ mm3 shows a simulated isolation better than −24.1 dB without any external decoupling measures and an envelope correlation coefficient (ECC) lower than 0.008. A four-antenna MIMO array is fabricated and measured to verify the feasibility. Across the operation band, the measured isolation of the antenna pair is better than −20.1 dB and other isolation levels are all better than −12.7 dB, the ECCs of any two antennas are lower than 0.13, and the total efficiency range of the four antennas is 35.2%~64.7%. The proposed dual antenna pair exhibits a great potential to be applied in future 5G MIMO smartphone.
TL;DR: In this paper, a novel filtering method based on the metasurface antenna (MSA) with radiation nulls is proposed without loading extra circuits, which can achieve the wideband filtering response in a low profile, as well as high gain with high aperture efficiency.
Abstract: A novel filtering method based on the metasurface antenna (MSA) with radiation nulls is proposed without loading extra circuits. Due to the specific multiunit structure of MSA, the filtering method is first realized on each radiating metasurface (MS) unit by introducing a multifolded U-shaped slot and a defected ground structure to generate lower edge radiation nulls. Meanwhile, coplanar parasitic patches are loaded around the MS units to provide upper edge nulls and simultaneously introduce extra in-band resonances for wide passband. Thus, a low-profile, wideband, and high-gain filtering antenna is readily constructed. To verify the concept, a prototype with a low profile of only $0.04\lambda _{{0}}$ is designed and fabricated. The simulated and measured results agree well, demonstrating a good performance with large impedance bandwidth of about 20%, high average gain of 8 dBi, and high aperture efficiency of about 90%, together with high out-of-band suppression levels of about 20 dB. In addition, the radiation patterns are symmetric in both the E- and H-planes with cross-polarization suppressions of over 20 dB. Compared with the reported filtering antennas, the proposed filtering MSA can achieve the wideband filtering response in a low profile, as well as high gain with high aperture efficiency.
TL;DR: In this paper, a dual-band metasurface based on a concentric rectangular arrangement was proposed to control the polarizations of both linearly and circularly polarized electromagnetic waves.
Abstract: Metamaterials offer the freedom to manipulate the polarization states of light at the subwavelength scale. However, previous designs generally made use of single resonance and, hence, only function for one specific incident polarization within a single-frequency band. In this paper, we present a dual-band metasurface based on a concentric rectangular arrangement to control the polarizations of both linearly and circularly polarized electromagnetic waves. We show that, on the one hand, the proposed metasurface structure can convert the polarization of linearly polarized waves to the cross direction in two broad frequency bands 4.40–5.30 GHz and 9.45–13.60 GHz. On the other hand, this design can also reflect circularly polarized waves without changing the handedness in two frequency bands 4.47–5.35 GHz and 9.57–13.57 GHz. For both cases, average polarization conversion efficiency larger than 86% was obtained in our experiment. The numerical simulations reveal that the dual-band cross-polarization coupling results from the strong electric and magnetic resonances between the top and bottom layers. The ultrathin polarization converter experimentally realized in this paper provides an important stepping stone for the future design of other dual-band metasurface devices and is believed to be extendable to higher frequency regimes.
TL;DR: In this article, a 3D-printed Luneburg lens with a simplified geometry is presented, where rod-type structures are employed as the unit cell of the gradient-index material to realize the required permittivity distribution in the lens.
Abstract: A 3-D-printed Luneburg lens with a novel simplified geometry is presented. The rod-type structures are employed as the unit cell of the gradient-index material to realize the required permittivity distribution in the lens. A prototype designed in the Ka -band is manufactured successfully by using a commercial 3-D printing facility. The substrate-integrated waveguide fed magnetoelectric (ME)-dipole antenna with endfire radiation is introduced as the feed for the Luneburg lens due to its wideband performance and compact configuration. By combining the lens with a set of the ME-dipoles, a millimeter-wave (mm-wave) multibeam Luneburg lens antenna is designed, fabricated, and measured. An overlapped impedance bandwidth of wider than 40% that can cover the entire Ka -band and mutual coupling below −17 dB are verified by the fabricated prototype. Nine stable radiation beams with a scanning range between ±61°, gain up to 21.2 dBi with a variation of 2.6 dB, and radiation efficiency of around 75% are achieved as well. With the advantages of good operating features, low fabrication costs, and ease of integration, the proposed multibeam Luneburg lens antenna would be a promising candidate for the fifth-generation (5G) mm-wave multiple-input multiple-output (MIMO) applications in 28 and 38 GHz bands.
TL;DR: The proposed design proves that 5G mm-wave antennas can be embedded to 4G systems without greatly sacrificing display size or sub-6 GHz antenna performance.
Abstract: Fifth generation (5G) mobile networks will introduce several new frequencies for short-range high-capacity communications. Future handsets must also support current frequency bands for backward compatibility and long-range communications. This paper presents a proof-of-concept solution for co-designed millimeter-wave (mm-wave) and Long Term Evolution (LTE) antennas in a metal-rimmed handset. The design shows that both antenna types can be accommodated in a shared volume and be integrated into the same structure. Presented antennas operate at 700–960 MHz, 1710–2690 MHz, and 25–30 GHz. Simulations and measurements suggest that the system can be designed in such a way that the mm-wave antenna does not hinder the low-band performance. LTE antennas generally reach over 60% total efficiency while the mm-wave module has a peak gain of 7 dBi with measurement-verified beam-steering capability. The proposed design proves that 5G mm-wave antennas can be embedded to 4G systems without greatly sacrificing display size or sub-6 GHz antenna performance.
TL;DR: In this paper, a dual-polarized band-absorptive frequency selective rasorber (FSR) is proposed in this communication, which is constructed by two-layer cascaded printed circuit boards, in which meanderline square loops with and without lumped resistors loaded on the top and bottom surfaces of the two substrates.
Abstract: A novel dual-polarized band-absorptive frequency selective rasorber (FSR) is proposed in this communication. The FSR is constructed by two-layer cascaded printed circuit boards, in which meander-line square loops with and without lumped resistors loaded on the top and bottom surfaces of the two substrates. Its operating principle is analyzed, and an accurate equivalent circuit model is presented. A prototype has been fabricated, assembled, and measured. The measured absorption band is from 4.8 to 6.81 GHz (34.6%), with a thickness of $\lambda _{\mathrm {a}}$ /8 at 4.8 GHz. Moreover, it is almost transparent to electromagnetic waves below 1.54 GHz. The measurement results achieve a good agreement with the simulated results, which verifies the effectiveness of the design.
TL;DR: In this article, a dual-band, low profile, high gain, and low specific absorption rate (SAR) triangular slotted monopole antenna with a $4\times 4$ artificial magnetic conductor (AMC) array is presented for WBAN applications.
Abstract: A dual-band, low profile, high gain, and low specific absorption rate (SAR) triangular slotted monopole antenna backed with a $4\times 4$ artificial magnetic conductor (AMC) array is presented for wireless body area network (WBAN) applications. The antenna is printed on a Rogers ULTRALAM 3850 substrate, whereas the AMC array is printed on a RO3003 substrate. The design operates at 3.5 GHz, for WiMAX wireless applications, and at 5.8 GHz for the ISM Band. The proposed antenna preserved the dual-band resonance and exhibited acceptable gain and SAR at a separation of 15 mm from the human body model. To reduce such separation and achieve enhancements to gain and SAR, an AMC array was utilized. In free space, gain enhancements by 6.8 and 3.7 dBi were achieved at both frequencies, respectively. Furthermore, over a gap of 1 mm from the human body, gain enhancements by 23.3 and 13.9 dBi were achieved at both frequencies, respectively. In addition, SAR reductions by almost 99% were attained. The antenna was fabricated and measured where a very good agreement was observed between simulated and measured results, with and without the incorporated AMC array. With such results, the proposed design can be highly recommended for wearable medical applications, specifically for diabetic patients.
TL;DR: The supervised descent method (SDM) for 2-D microwave imaging is studied to incorporate prior information into inversion and reduce the computational complexity in the online inversion.
Abstract: In mymargin this communication, we study the application of the supervised descent method (SDM) for 2-D microwave imaging. SDM contains offline training and online prediction. In the offline stage, a training data set is generated according to prior information. Then, the average descent directions between a fixed initial model and the training models can be learned by iterative schemes. In the online stage, model reconstruction is achieved through iterations based on learned descent directions. This scheme offers a new perspective to incorporate prior information into inversion and reduce the computational complexity in the online inversion. Synthetic examples validate the accuracy and efficiency of this method.
TL;DR: In this paper, a dual-linear polarized tightly coupled dipole array with integrated balun operating across a 9:1 bandwidth, from 2 to 18 GHz, is presented, where the traditional dielectric superstrate is replaced with double layers of frequency selective surfaces to enable scanning down to 60° in both E-, H-, and diagonal (D)-planes across the entire band.
Abstract: We present, for the first time, a novel dual-linear polarized tightly coupled dipole array with integrated balun operating across a 9:1 bandwidth, from 2 to 18 GHz. This dual-linear polarized array employs a tightly coupled dipole topology and scans down to 60° from boresight. The overall geometry consists of cross-located tightly coupled dipoles integrated with a folded Marchand balun that serves as an impedance transformer to achieve a wideband feeding network. Notably, the traditional dielectric superstrate is replaced with double layers of frequency selective surfaces to enable scanning down to 60° in both E-, H-, and diagonal (D)-planes across the entire band. The design achieves VSWR $\lambda _{low}$ /10). The design is validated through fabrication and testing of an $11 \times 11$ prototype. The measurements of this prototype are presented and are in good agreement with simulations.
TL;DR: In this article, a planar array antenna with omnidirectional radiation in horizontal plane is proposed for the 26 GHz fifth-generation (5G) broadcast applications, which is composed of two dipoles and a substrate integrated cavity (SIC) as the power splitter.
Abstract: In this paper, a compact, broadband, planar array antenna with omnidirectional radiation in horizontal plane is proposed for the 26 GHz fifth-generation (5G) broadcast applications. The antenna element is composed of two dipoles and a substrate integrated cavity (SIC) as the power splitter. The two dipoles are placed side-by-side at both sides of the SIC, and they are compensated with each other to form an omnidirectional pattern in horizontal plane. By properly combing the resonant frequencies of the dipoles and the SIC, a wide impedance bandwidth from 24 to 29.5 GHz is achieved. To realize a large array while reducing the complexity, loss, and size of the feeding network, a novel dual-port structure combined with radiation and power splitting functions is proposed for the first time. The amplitude and phase on each element of the array can be tuned, and therefore, the grating lobes level can be significantly reduced. Based on the dual-port structure, an eight-element array with an enhanced gain of over 12 dBi is designed and prototyped. The proposed antenna also features low profile, low weight, and low cost, which is desirable for 5G commercial applications. Measured results agree well with the simulations, showing that the proposed high-gain array antenna has a broad bandwidth, omnidirectional pattern in horizontal plane, and low side-lobes.
TL;DR: In this article, a wideband filtering patch antenna is investigated, which consists of one upper and two lower horizontal arms, as well as a vertical arm that connects them, and two probe modes along with a patch mode are simultaneously excited within the passband, producing a wide bandwidth of 21.3%.
Abstract: A wideband filtering patch antenna is investigated in this paper. The patch antenna is fed by an F-shaped probe, which consists of one upper and two lower horizontal arms, as well as a vertical arm that connects them. Owing to the novel excitation scheme, two probe modes along with a patch mode are simultaneously excited within the passband, producing a wide bandwidth of 21.3% with stable antenna gains and radiation patterns. Meanwhile, cross-coupling is constructed in the antenna, generating two symmetrical radiation nulls right at the two sides of the passband. Consequently, a compact filtering antenna with bandpass response and high selectivity is obtained, without utilizing any extra filtering circuit. This design is also extended to realize a reconfigurable filtering antenna. Two varactor diodes are embedded in the F-shaped probe to continuously tune the frequency of the operating band from 2.05 to 2.52 GHz. The antenna bandwidth can be flexibly tuned from 2.2% to 21.3%, and simultaneously good filtering performance is kept during the tuning of different states.
TL;DR: In this paper, the authors proposed a method of suppressing cross-band scattering in dual-band dual-polarized antenna arrays by introducing chokes into lowband (LB) elements to suppress high-band (HB) scattering currents.
Abstract: This paper presents a novel method of suppressing cross-band scattering in dual-band dual-polarized antenna arrays. The method involves introducing chokes into low-band (LB) elements to suppress high-band (HB) scattering currents. The experimental results show that by inserting LB-pass HB-stop chokes into LB radiators, suppression of induced HB currents on the LB elements is achieved. This greatly reduces the pattern distortion of the HB array caused by the presence of LB elements. The array considered is configured as two columns of HB antennas operating from 1.71 to 2.28 GHz interleaved with a single column of LB antennas operating from 0.82 to 1.0 GHz. The realized array with choked LB element has stable and symmetrical radiation in both HB and LB.
TL;DR: In this paper, a dual-polarized multiband array is proposed and developed for 2G/3G/4G base station applications, which consists of two-element lower band array, five-element higher band array and bowl-shaped reflector.
Abstract: A compact, dual-polarized multiband array is proposed and developed for 2G/3G/4G base station applications. The antenna is formed by two-element lower band array, five-element higher band array, bowl-shaped reflectors, bended baffles, and rectangular baffles, which are coexisting over one reflector. Miniaturized higher band element covering 2G/3G/4G bands and new square-shaped aperture lower band element covering LTE700/GSM850/GSM900 have been proposed. The higher band elements are placed upon the bowl-shaped reflector and composed of two pairs of loop dipoles with chamfers and vertical stubs for miniaturization. The bowl-shaped reflector is of great significance to the stable beamwidth, while the rectangular and bended baffles are designed further to improve the beamwidth. Moreover, the five-element higher band array is designed with electric downtilt from 0° to 10°. The measured results determined by VSWR <1.7 are with the whole broadband coverage from 0.698 to 0.96 and 1.7 to 2.7 GHz, which can cover the whole 2G/3G/4G bands. Furthermore, the stable half-power beamwidth of 65.9 ± 4.3° at the horizontal plane (H-plane) as well as stable gain and enhanced cross-polarization discrimination (XPD) are achieved within both higher and lower frequency bands.
TL;DR: In this article, a compact MIMO antenna for 5G mobile terminals is presented, which consists of four tightly arranged elements and three lumped components, and the measured −6 dB bandwidth of the antenna is 135 MHz, with port isolation higher than 11.6 dB.
Abstract: In this paper, a compact multiple-input multiple-output (MIMO) antenna is presented for 5G mobile terminals. The antenna consists of four tightly arranged elements and three lumped components. The edge-to-edge distance between adjacent elements is only 1 mm. It is found that adding an inductor at the current minimum location or a capacitor at the current maximum location of two elements can significantly reduce the mutual coupling. Based on high-isolated dual-element structures, a four-element MIMO antenna is experimentally analyzed for 3400–3600 MHz band. The size of the antenna is only $40.8 \times 3$ mm2. The measured −6 dB bandwidth of the antenna is 135 MHz, with port isolation higher than 11.6 dB. In addition, a vertically placed four-element MIMO antenna is designed with a size of $38.2\times3.2$ mm2. No ground clearance is needed between the antenna and the chassis ground.
TL;DR: In this article, a new type of metasurface with both phase and amplitude modulations is proposed, which is composed of C-shaped particles and can generate and control multiple beams using amplitude and phase responses simultaneously.
Abstract: Owing to the capability of providing a certain phase gradient on the interface between two media, metasurfaces have shown great promise for altering the directions of outgoing electromagnetic (EM) waves arbitrarily. With the suitable arrangement of particles on metasurfaces, anomalous reflection and refraction have been observed in wide frequency ranges. To completely control the propagation of EM waves, both phase and amplitude profiles are required in some applications. Herein, we propose a new type of metasurface with both phase and amplitude modulations, which is composed of C-shaped particles and can generate and control multiple beams using amplitude and phase responses simultaneously. An addition theorem of complex reflection coefficients is presented to acquire various states of multiple beams reflected from designed metasurfaces. Meanwhile, the intensities of multiple beams can be separately modulated as desired benefitting from the independent controls of phase and amplitude profiles. All the experimental results have good agreements with the numerical simulations. The presented method opens a new way to form and manipulate multiple beams using metasurfaces, which can find potential applications in beam shaping, radar detection systems, and high-quality holography.
TL;DR: A novel technique for surrogate modeling of antenna structures is proposed that involves a construction of two levels of surrogates, both realized as kriging interpolation models and allows uniform allocation of training data samples in a straightforward manner.
Abstract: Utilization of electromagnetic (EM) simulation tools is mandatory in the design of contemporary antenna structures. At the same time, conducting design procedures that require multiple evaluations of the antenna at hand, such as parametric optimization or yield-driven design, is hindered due to the high cost of accurate EM analysis. To a certain extent, this issue can be addressed using fast replacement models (also referred to as surrogates). Unfortunately, due to curse of dimensionality, traditional data-driven surrogate modeling methods are limited to antenna structures described by a few parameters with relatively narrow parameter ranges. This is by no means sufficient given the complexity of modern designs. In this paper, a novel technique for surrogate modeling of antenna structures is proposed. It involves a construction of two levels of surrogates, both realized as kriging interpolation models. The first model is based on a set of reference designs optimized for selected performance figures. It is used to establish a domain for the final (second level) surrogate. This formulation permits efficient modeling within wide ranges of antenna geometry parameters and wide ranges of performance figures (e.g., operating frequencies). At the same time, it allows uniform allocation of training data samples in a straightforward manner. Our approach is demonstrated using two microstrip antenna examples and is compared with conventional kriging and radial basis function modeling. Application examples for antenna optimization are also provided along with experimental validation.
TL;DR: In this article, a dual-function slot antenna at microwave and millimeter-wave (mm-wave) band is proposed, which consists of a slot printed on the edge of the structure ground plane.
Abstract: A dual-function slot antenna at microwave and millimeter-wave (mm-wave) band is proposed. The design consists of a slot printed on the edge of the structure ground plane. A short-circuited varactor diode (VAR) is used to achieve the frequency tunability from 2.05 to 2.7 GHz (4G, WLAN) with a maximum realized gain of 4.5 dBi. For mm-waveband, the slot works as a connected slot antenna array (CSAA) by using eight periodic feeders with a wide bandwidth of 23–29 GHz (5G) and a maximum realized gain of 12.5 dBi. To enhance the functionality, two slots are orthogonally arranged for multiple-input multiple-output (MIMO) application. The whole structure is implemented using Rogers 5880 substrate with a board size of $70\times 60\times 0.381$ mm3. The envelope correlation coefficient (ECC) and isolation are calculated, showing satisfactory MIMO characteristics. The minimum ECC value is 0.01, while the isolation is more than 20 dB among different feeding ports. Due to the integration of 4G and 5G operations into a single narrow slot, the proposed antenna system is compact, simple, and planar in structure and, thus, attractive for future mobile handheld devices.
TL;DR: In this paper, a single-layer corporate-feed antenna with single-layered corporate feed based on the ridge gap waveguide (RGW) technology in the 60 GHz band is presented.
Abstract: This paper presents an $8\times 8$ -element slot array antenna with single-layered corporate-feed based on the ridge gap waveguide (RGW) technology in the 60 GHz band. As is well known, a corporate-feed slot array antenna usually has backed cavities to increase the bandwidth and provides a space for its distribution network, and therefore three layers in total: one layer for radiating slots and two layers for feed network with one layer of back cavities and the other one of power dividers. The antenna in this paper is designed by utilizing only two separate metallic layers–a corporate-feed network layer and a radiating slot layer. Compared with the conventional three-layered slot array antennas, the proposed antenna avoids the utilization of the backed cavity layer so that its complexity and manufacture cost decrease. In order to solve the problem of the narrow bandwidth caused by taking away the backed cavities, we utilize double-ridged radiating slots instead of the conventional rectangular ones. A compact transition power divider from standard waveguide WR-15 to the RGW is introduced to excite the proposed array antenna. The $8\times 8$ -element slot array antenna has been fabricated by computerized numerical control machining technique. The measured results demonstrate that the −10 dB reflection coefficient has around 17% bandwidth covering 56.5–67 GHz frequency range, and the measured gain is better than 26 dBi with more than 70% antenna efficiency over 58–66 GHz.
TL;DR: In this paper, a 1-bit 256-element reconfigurable transmitarray antenna (RTA) at the Ku-band is presented, which consists of two orthogonal H-shaped slots as receiving and transmitting structures.
Abstract: A novel 1-bit 256-element reconfigurable transmitarray antenna (RTA) at the Ku-band is presented. The element consists of two orthogonal H-shaped slots as receiving and transmitting structures, and the power transmission is realized by a coupling microstrip line in between. Two p-i-n diodes integrated on the coupling line can be electronically controlled to reverse the excitation directions, thus generating two states with 180° phase difference and low transmission loss. A subwavelength element spacing of $\lambda _{0}$ /3 is utilized to stabilize the element performance under oblique incidence. A transmitarray prototype with $16 \times 16$ elements and aperture size of $5.3\lambda _{0}\times 5.3\lambda _{0}$ at 12.5 GHz is fabricated and measured for the experimental verification. The measured results show that the maximum gain is 17.0 dBi with an aperture efficiency of 14.0%, and 2-D scanning beams within ±50° angular range are obtained. The 3-dB gain bandwidth of the broadside beam is 9.6%.