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In this research, we present an innovative method for estimating the beams of array antennas. Traditional beam analysis methods rely on placing receiving antennas in the far-field region, which requires moving or rotating the Tx or Rx, and using radiation pattern measurements. However, such methods often demand vast spatial requirements and the use of high-cost network analyzers. In contrast, the technique proposed in this study utilizes a board patterned with coupling lines strategically placed in the antenna’s near-field zone. Signals intercepted by these coupling lines undergo conversion into DC voltage via a power detector situated at the line terminus. Interestingly, this method enables beam estimation solely based on the DC voltage level output of the power detector, thus offering a cost-effective and space-efficient solution that represents a significant advancement from traditional beam estimation methods.

Background Purpose Methods Results Conclusion During magnetic resonance‐guided focused ultrasound (MRgFUS) surgery for uterine fibroids, ablation of fibrous tissues in proximity to the hips and spine is challenging due to heating within the bone that can cause patients to experience pain and potentially damage nerves. This far‐field bone heating limits the volume of fibroid tissue that is treatable via MRgFUS.To investigate transducer module apodization for improving the ratio of focal‐to‐bone heating (ΔTratio$\Delta T_{\mathrm{ratio}}$) when targeting fibroid tissue close to the hips and spine, to enable MRgFUS treatments closer to the bone.Acoustic and thermal simulations were performed using 3D magnetic resonance imaging (MRI)‐derived anatomies of ten patients who underwent MRgFUS ablation for uterine fibroids using a low‐frequency (0.5MHz$0.5 \ \text{MHz}$) 6144‐element flat fully‐populated modular phased array system (Arrayus Technologies Inc., Burlington, Canada) at our institution as part of a larger clinical trial (NCT03323905). Transducer modules (64elements$64 \ \text{elements}$ per module) whose beams intersected with no‐pass zones delineated within the field were identified, their output power levels were reduced by varying blocking percentage levels, and the resulting temperature field distributions were evaluated across multiple sonications near the hip and spine bones in each patient. Acoustic and thermal simulations took approximately 20min$20 \ \text{min}$ (7min$7 \ \text{min}$) and 1min$1 \ \text{min}$ (30s$30 \ \text{s}$) to run for a single near‐spine (near‐hip) target, respectively.For all simulated sonications, transducer module blocking improved ΔTratio$\Delta T_{\mathrm{ratio}}$ compared to the no blocking case. In just over half of sonications, full module blocking maximized ΔTratio$\Delta T_{\mathrm{ratio}}$ (increase of 82% ±$\pm$ 38% in 50% of hip targets and 49% ±$\pm$ 30% in 62% of spine targets vs. no blocking; mean ± SD), at the cost of more diffuse focusing (focal heating volumes increased by 13% ± 13% for hip targets and 39% ± 27% for spine targets) and thus requiring elevated total (hip: 6% ± 17%, spine: 37% ± 17%) and peak module‐wise (hip: 65% ± 36%, spine: 101% ± 56%) acoustic power levels to achieve equivalent focal heating as the no blocking control case. In the remaining sonications, partial module blocking provided further improvements in both ΔTratio$\Delta T_{\mathrm{ratio}}$ (increased by 29% ± 25% in the hip and 15% ± 12% in the spine) and focal heating volume (decrease of 20% ± 10% in the hip and 34% ± 17% in the spine) relative to the full blocking case. The optimal blocking percentage value was dependent on the specific patient geometry and target location of interest. Although not all individual target locations saw the benefit, element‐wise phase aberration corrections improved the average ΔTratio$\Delta T_{\mathrm{ratio}}$ compared to the no correction case (increase of 52% ± 47% in the hip, 35% ± 24% in the spine) and impacted the optimal blocking percentage value. Transducer module blocking enabled ablative treatments to be carried out closer to both hip and spine without overheating or damaging the bone (no blocking: 42±1mm$42\pm 1 \ \text{mm}$/17±2mm$17 \pm 2 \ \text{mm}$, full blocking: 38±1mm$38\pm 1 \ \text{mm}$/8±1mm$8\pm 1 \ \text{mm}$, optimal partial blocking: 36±1mm$36\pm 1 \ \text{mm}$/7±1mm$7\pm 1 \ \text{mm}$ for hip/spine).The proposed transducer apodization scheme shows promise for improving MRgFUS treatments of uterine fibroids, and may ultimately increase the effective treatment envelope of MRgFUS surgery in the body by enabling tissue ablation closer to bony structures. [ABSTRACT FROM AUTHOR]

Two-dimensional leaky-wave antennas (LWAs) are a class of planar, traveling-wave radiators with attractive features of a low profile, ease of feeding, frequency reconfigurability of the radiation pattern, and polarization agility. Their use in conjunction with array feeders has been the subject of various investigations in recent decades, thanks to the additional degrees of freedom provided by the presence of multiple independent sources. Here, we provide a review of some of the most recent and promising array-fed two-dimensional (2-D) LWAs, selecting a couple of the most significant structures in application, namely Fabry–Perot cavity antennas and bull's-eye antennas, and discussing some of their recently proposed advanced features. [ABSTRACT FROM AUTHOR]

In a software-defined radar (SDR) system, most of the signal processing usually implemented in hardware is implemented by software, thus allowing for higher flexibility and modularity compared to conventional radar systems. However, the majority of SDR demonstrators and proofs of concept reported in the open literature so far have been based on simple antenna systems. As a result, the full potentialities of an SDR approach have not been completely exploited yet. In this work, we propose a flexible antenna module to be integrated into an active electronically scanning array (AESA) with controlled sidelobe level over a wide angular range, exhibiting polarization reconfigurability with a low cross-polarization level and high isolation. For this purpose, analytical and numerically efficient techniques for the synthesis of the aperture distribution and the correct evaluation of the radiating features (e.g., beamwidth, pointing angle, sidelobe levels, etc.) are presented in order to grant real-time control of the digital beamforming network. A sub-array module demonstrator is fabricated and measured to corroborate the concept. [ABSTRACT FROM AUTHOR]

In this paper we describe a class of printed patch antennas that involve 3 metal layers completely integrated within a single dielectric, which are of very high efficiency and significant gain. The antennas presented have dual linear polarization and sufficient impedance matching bandwidth to be suited for sub-6 5G applications, producing advantageous antenna arrays monolithically integrated into a single planar PCB that are thin and lightweight. The feeding mechanism of the antennas is through an intermediate dedicated metal layer designed appropriately as a coupler, coupling the input power at the feeding ports of the structure to the antenna without a direct metal contact to the radiating patch. The multilayer design allows monolithic integration of multi-element combiners and phase shifters within the PCB of antenna arrays and results in compact monolithic scanning arrays. Theoretical full-wave simulations and measurements of fabricated prototypes are in very good agreement and validate the proposed designs. [ABSTRACT FROM AUTHOR]

An inverted-L monopole radiating element is proposed for antenna-in-package modules at the 151.5-164 GHz band. Its radiation pattern is half-isotropic and is well-suited for phased arrays for mobile communications. The ideal inverted-L monopole is analyzed and initial design parameters are found. A radiating element structure designed for planar technology is proposed, which consists of eight copper layers and is fed by a stripline. Impedance matching and fabrication constraints are taken into consideration when designing the structure. An array is designed and fabricated with the same size and technology as the module. To prove its scanning capabilities, a scaled-up version of the array is fabricated and measured at 28 GHz. The beam coverage of the proposed arrays is very high, able to cover 80% with a realized gain of 10 dBi by using just 2 modules.

In this paper, a novel ultrawideband phased array is presented based on exponential curve modified dipoles. A tightly-coupled exponential curve modified dipole arm is used to extend the operating bandwidth with a simple coplanar strip structure, which avoids the use of additional complex impedance conversion networks and reduces the processing difficulty and cost. The problematic common-mode resonance is moved out of the required operating bandwidth by the shorting pin. A wide angle impedance matching layer is used to improve beam scanning ability of the array. The proposed antenna array achieves 8.5:1 (2.06-17.6 GHz) bandwidth at broadside, with a scanning range of ±45° from 2.06-17.6 GHz (8.5:1 bandwidth) in the E-plane and ±45° from 2.2-17.6 GHz (8:1 bandwidth) in the H-plane, subject to active VSWR < 3. A $6\times6$ prototype was fabricated and measured with good agreement in measured and simulated results, which verify the ultrawideband performance of proposed array.

A low-profile dual-polarized magneto electric (ME) dipole antenna configuration implemented on standard multilayer PCB technology is here reported. The proposed radiator is conceived for dual-polarized 28 GHz 5G phased array applications. Wideband operation is achieved by applying several low-frequency techniques which allow to fulfil the 5G requirements without increasing the dielectric core thickness. A $4\times8$ ME-dipole phased array is then designed, fabricated, and tested. The measured beam scanning range without the blindness in the E-plane is ±55° for the vertical polarization. Stable radiation patterns and a gain of up to 22 dBi are also achieved. The thickness of the antenna layers is significantly lower with respect to the other configurations in the literature while providing similar performance. Having reduced the antenna core thickness results in a structurally balanced stack-up, lighter and easier to fabricate with high yield. In addition, high isolation between the elements allows superior beam scanning performances. The proposed design is well suited to both packaging technologies and standard PCB processes and is an attractive candidate for the millimeter-wave applications in the fifth generation (5G) mobile systems.

Distance sensors are important for mobile robots to perceive surrounding environment. Typical sensors like LiDARs and depth cameras have been widely used, yet each has its limitations, such as LiDARs’ relatively high cost, depth cameras’ limitation to indoor use, and their poor performance in detecting transparent objects directly. On the other hand, ultrasonic phased array that integrates multiple ultrasonic sensors not only enables 3D ranging and imaging, but also provides advantages of strong environmental adaptability, being cost-effective and being able to detect transparent objects. To explore the application of in-air ultrasonic phased arrays for mobile robots, we simulate a 40 kHz $5\times 5$ non-uniform sparse ultrasonic phased array. The simulator emulates the process of phased array transmission and reception, and utilizes algorithms such as beamforming and matched filtering to obtain depth information in three-dimensional space. Then, a multi-view indoor 3D reconstruction method fusing the ultrasonic phased array and a monocular camera is proposed, where two scanning strategies are developed to handle different scenarios. Finally, the method is validated in different Gazebo scenarios and compared with other baseline methods like LiDARs and depth cameras. The experimental results reveal the method’s strong performance in terms of accuracy, consistency and completeness.

Reconfigurable intelligent surface (RIS)-aided near-field communications are investigated. First, the necessity of investigating RIS-aided near-field communications and the advantages brought about by the unique spherical wave-based near-field propagation are discussed. Then, the family of patch array-based RISs and metasurface-based RISs is introduced along with respective near-field channel models. A pair of fundamental performance limits of RIS-aided near-field communications, namely, their power scaling law and effective degrees of freedom (EDOF), are analyzed for both patch array-based and metasurface-based RISs, which reveals the potential performance gains that can be achieved. Furthermore, associated near-field beam training and beamforming design issues are studied, where a two-stage hierarchical beam training approach and a low-complexity element-wise beamforming design are proposed for RIS-aided near-field communications. Finally, a suite of open research problems is highlighted for motivating future research. [ABSTRACT FROM AUTHOR]

Performance of digitally beamformed phased arrays relies on accurate calibration of the array by obtaining gains of each antenna in the array. The stations of the Square Kilometer Array‐Low (SKA‐Low) are such digital arrays, where the station calibration is currently performed using conventional interferometric techniques. An alternative calibration technique similar to holography of dish based telescopes has been suggested in the past. In this paper, we develop a novel mathematical framework for holography employing tensors, which are multi‐way data structures. Self‐holography using a reference beam formed with the station under test itself and cross‐holography using a different station to obtain the reference beam are unified under the same formalism. Besides, the relation between the two apparently distinct holographic approaches in the literature for phased arrays is shown, and we show that under certain conditions the two methods yield the same results. We test the various holographic techniques on an SKA‐Low prototype station Aperture Array Verification System 2 (AAVS2) with the Sun as the calibrator. We perform self‐holography of AAVS2 and cross‐holography with simultaneous observations carried out with another station Engineering Development Array 2. We find the results from the holographic techniques to be consistent among themselves as well as with a more conventional calibration technique. Key Points: A framework for phased array holography using tensors is presentedMultiple holographic techniques are unifiedSelf‐holography and cross‐holography of Aperture Array Verification System 2 are performed and the results compared [ABSTRACT FROM AUTHOR]

Two-dimensional leaky-wave antennas (LWAs) are a class of planar, traveling-wave radiators with attractive features of a low profile, ease of feeding, frequency reconfigurability of the radiation pattern, and polarization agility. Their use in conjunction with array feeders has been the subject of various investigations in recent decades, thanks to the additional degrees of freedom provided by the presence of multiple independent sources. Here, we provide a review of some of the most recent and promising array-fed two-dimensional (2-D) LWAs, selecting a couple of the most significant structures in application, namely Fabry–Perot cavity antennas and bull’s-eye antennas, and discussing some of their recently proposed advanced features.

In a software-defined radar (SDR) system, most of the signal processing usually implemented in hardware is implemented by software, thus allowing for higher flexibility and modularity compared to conventional radar systems. However, the majority of SDR demonstrators and proofs of concept reported in the open literature so far have been based on simple antenna systems. As a result, the full potentialities of an SDR approach have not been completely exploited yet. In this work, we propose a flexible antenna module to be integrated into an active electronically scanning array (AESA) with controlled sidelobe level over a wide angular range, exhibiting polarization reconfigurability with a low cross-polarization level and high isolation. For this purpose, analytical and numerically efficient techniques for the synthesis of the aperture distribution and the correct evaluation of the radiating features (e.g., beamwidth, pointing angle, sidelobe levels, etc.) are presented in order to grant real-time control of the digital beamforming network. A sub-array module demonstrator is fabricated and measured to corroborate the concept.

This paper presents an innovative technique to synthesize a virtual antenna array (VAA) that consumes less energy than conventional antenna arrays that are used in mobile communications systems. We have shown that for a specific spectral efficiency a wireless system using the proposed virtual antenna array consumes significantly less energy per bit (∼3 dB) than a wireless system using a conventional multiple-input multiple-output (MIMO) array. This means the adoption of the proposed VAA technology in smartphones, iPad, Tablets and even base-stations should significantly reduce the carbon footprint of wireless systems. The proposed VAA is realized by employing a pair of linear antenna arrays that are placed in an orthogonal configuration relative to each other. This orthogonal arrangement ensures the radiation is circularly polarized. The size of the standard radiating elements constituting the VAA were miniaturized using the topology optimization method. The design of the VAA incorporates substrate integrated waveguide (SIW) and metasurface technologies. The function of SIW in the design was twofold, namely, to reduce energy loss in the substrate on which the VAA is implemented, and secondly to mitigate unwanted electromagnetic interactions between the neighboring radiating elements and thereby enhancing isolation which otherwise would degrade the radiation characteristics of the array. Metasurface technology served to effectively increase the effective aperture of the array with no impact on the footprint of the array. The consequence of SIW and metasurface technologies was improvement in the gain and radiation efficiency of the array. The proposed four orthogonal 4-element VAA covers the entire sub-5 GHz frequency range, and it radiates bidirectional in the azimuth plane and omni-directional in the elevation plane. Moreover, it is relatively easy to design and fabricate. The proposed VAA has dimensions of 0.96λ0 × 0.96λ0 × 0.0016λ0 at mid-band frequency of 3 GHz. VAA has a measured gain of 25 dBi and radiates with 90% efficiency. The average isolation between the linear arrays constituting the virtual array is better than 27 dB.

Currently, phased arrays are increasingly used in ultrasonic nondestructive testing. One of the most important parameters of ultrasonic nondestructive testing with the application of phased arrays is the angular resolution. This paper presents the results of studies of the angular resolution of concave and convex acoustic arrays in ultrasonic testing with the application of the total focusing method. Computer modeling of concave and convex acoustic arrays consisting of 16, 32 and 64 elements with distances between elements of 0.5 and 1 mm and arc radii of 30 and 60 mm have been performed. The results obtained by computer modeling were confirmed via in situ experiments. [ABSTRACT FROM AUTHOR]

The development of novel and innovative phased array designs toward affordable and performance‐oriented solutions has become the dire need of modern‐age wireless communication technologies. This paper proposed an unconventional method to design phased array antennas by eliminating the need of phase shifters. A cost‐effective alternative is presented by using "time‐modulation" based arrays capable of beam steering and electronic scanning. Controlling the high‐speed absorptive switches connected with each radiating elements in a periodic manner to generate the desired amplitude and phase tapering is the main purpose of these time‐domain arrays. So, the need for expensive phase shifters and erroneous attenuators can be avoided. This article explored the idea of "time‐modulation" to design innovative and efficient phased arrays for monopulse and multifunction radar systems. Suitable switching sequences are designed to produce simultaneous sum‐difference radiation patterns for monopulse tracking radars, and simultaneous scanned beam patterns for multifunction radars. To achieve the desired objectives, time‐modulated linear arrays of 10, 20, and 30 elements are proposed with appropriate switching sequences. The parameters of the arrays such as switch‐ON instants, switch‐ON periods, and switch‐OFF instants are controlled by employing the crow search optimization (CSO) algorithm. Representative results for both the applications are elaborated and compared with recently published counterpart designs to present the potentialities of the proposed concept for electronic steering and beam scanning applications. [ABSTRACT FROM AUTHOR]

This letter presents a novel method used to find the constant false alarm rate (CFAR) threshold after coherently compressing one or more dimensions of the radar image, generally the ones obtained from a phased array or multiple input multiple output (MIMO) diversity. The method provides a significantly large improvement in the numerical complexity of the processing chain at the cost of a slightly lower probability of detection for a fixed probability of false alarm. The method is particularly useful for real-time applications such as assisted and autonomous driving, where CFAR is applied to the range-Doppler map to generate a point cloud before angular estimation is done. The method may also be extended for Earth observation (EO) or surveillance applications where real-time processing is required. The proposed method is intended as a pre-processing step to the CFAR detection and is compatible with any CFAR algorithm that assumes Gaussian noise. The method implies finding a CFAR threshold calculated from a low-SNR non-coherent integrated radar signal and analytically mapping it to the high-SNR coherent integrated radar signal for improved detection. The proposed method is first presented theoretically and then evaluated in both simulated and experimental environments. [ABSTRACT FROM AUTHOR]

Slanting of subarrays in a hybrid MIMO configuration is known to mitigate loss from directional antenna elements typical of mmWave integrated circuit arrays, under the line-of-sight (LOS) plane wave model (PWM) of propagation. This paper considers optimal slanting of subarrays under the spherical wave model (SWM) of propagation, because the SWM is known to be more appropriate than PWM for short-range LOS MIMO channels. The capacity of MIMO under the LOS SWM is known to depend on subarray spacing for non-slanted subarrays, so this paper derives the optimal spacing for slanted subarrays, which is shown to be the same as for non-slanted subarrays. The paper goes on to show that slanting only degrades hybrid MIMO capacity under the SWM model. By comparing the capacities under the PWM and SWM, the authors explain why slanting is beneficial under one model and not under the other.

To enhance the capabilities of high-resolution imaging or beamforming, the trend goes towards arrays with high-channel count and large aperture sizes. The operation at increasing mm-wave frequencies exacerbates the consequences of manufacturing tolerances on the array performance, further necessitating the development of high-quality calibrations. Thereby, a large number of array response vectors, addressed in the following as data points, is stored. Typically, one data point is measured at a time for each angle. To reduce the calibration effort, hereby defined as the number of required measurements, a calibration setup employing active calibration targets (ACT) is proposed. This setup allows the storage of a multitude of data points within a single measurement. In addition, this measurement setup is placed in the near-field of the array to relax the requirements on the size of the anechoic chamber. Employing multiple targets makes it challenging to compensate the near-field effects. Therefore, methods are discussed to ensure a consistent quality of the calibration considering the near-field influences from the ACTs. Exemplary measurements deploying an antenna array operating at 78.5 GHz demonstrate that this calibration measurement setup employing three ACTs placed in the near-field of the array reduces the calibration effort by a factor of 3 compared to state-of-the-art setups. The average deviation of the antenna phase relations amounts to 4.1 degree, proving that the presented setup achieves the same calibration quality as state-of-the-art setups.

The utilization of efficient digital self-interference cancellation technology enables the simultaneous transmit and receive (STAR) phased array system to meet most application requirements through STAR capabilities. However, the development of application scenario requirements makes array configuration technology for STAR phased arrays increasingly important. Thus, this paper proposes a sparse shared aperture STAR reconfigurable phased array design based on beam constraints which are achieved by a genetic algorithm. Firstly, a design scheme for transmit and receive arrays with symmetrical shared apertures is adopted to improve the aperture efficiency of both transmit and receive arrays. Then, on the basis of shared aperture, sparse array design is introduced to further reduce system complexity and hardware costs. Finally, the shape of the transmit and receive arrays is determined by constraining the side lobe level (SLL), main lobe gain, and beam width. The simulated results indicate that the SLL of the transmit and receive patterns under beam-constrained design have been reduced by 4.1 dBi and 7.1 dBi, respectively. The cost of SLL improvement is a reduction in transmit gain, receive gain, and EII of 1.9 dBi, 2.1 dBi, and 3.9 dB, respectively. When the sparsity ratio is greater than 0.78, the SLL suppression effect is also significant, and the attenuation of EII, transmit, and receive gains do not exceed 3 dB and 2 dB, respectively. Overall, the results demonstrate the effectiveness of a sparse shared aperture design based on beam constraints in producing high gain, low SLL, and low-cost transmit and receive arrays. [ABSTRACT FROM AUTHOR]

In this paper, we propose for the first time a novel feed approach to a tightly coupled dipole array (TCDA). Firstly, compact zigzagging microstrip feedlines are utilized as baluns to feed our array elements to obtain wideband impedance-matching characteristics. Secondly, this array is designed on ultrathin substrates aiming at obtaining ultra-tight coupling between the dipole arms of two neighboring elements. Some irreplaceable parasitic pads are developed and added to the radiating arms to improve both the impedance and radiation characteristics of the TCDA. With these technologies, a 12 × 12 TCDA prototype is designed, fabricated and measured for verification. The array achieves an impressive impedance bandwidth spanning of 4–18 GHz for S 11 < − 10   dB . Its radiation patterns and realized gain are measured to verify its stable electromagnetic characteristics. Its realized gain is from 15 dB to 25 dB within the operating frequency band. Its efficiency is around 91%. Its measured results show good agreement with simulations. [ABSTRACT FROM AUTHOR]

Future wireless communications require higher security as well as a higher data rate. We have been studying physically secured wireless transmission systems and previously proposed encryption/decryption techniques based on the AND operation caused by coherent detection between two encrypted data sequences on two different terahertz carriers. Furthermore, we suggested that by employing the XOR operation as the decryption, the proposed system can be made more secure because XOR increases the computational complexity for eavesdroppers to recover the plaintext. In this paper, we propose the XOR operation between two data sequences on FSK-modulated terahertz waves. By constructing the XOR encryption transmitters/receivers, which consisted of high-speed wavelength tunable lasers and arrayed uni-traveling-carrier photodiodes (UTC-PDs), we successfully demonstrated the XOR operation between two data sequences on 200 GHz waves from the two transmitters. [ABSTRACT FROM AUTHOR]

This paper presents an innovative technique to synthesize a virtual antenna array (VAA) that consumes less energy than conventional antenna arrays that are used in mobile communications systems. We have shown that for a specific spectral efficiency a wireless system using the proposed virtual antenna array consumes significantly less energy per bit (∼3 dB) than a wireless system using a conventional multiple-input multiple-output (MIMO) array. This means the adoption of the proposed VAA technology in smartphones, iPad, Tablets and even base-stations should significantly reduce the carbon footprint of wireless systems. The proposed VAA is realized by employing a pair of linear antenna arrays that are placed in an orthogonal configuration relative to each other. This orthogonal arrangement ensures the radiation is circularly polarized. The size of the standard radiating elements constituting the VAA were miniaturized using the topology optimization method. The design of the VAA incorporates substrate integrated waveguide (SIW) and metasurface technologies. The function of SIW in the design was twofold, namely, to reduce energy loss in the substrate on which the VAA is implemented, and secondly to mitigate unwanted electromagnetic interactions between the neighboring radiating elements and thereby enhancing isolation which otherwise would degrade the radiation characteristics of the array. Metasurface technology served to effectively increase the effective aperture of the array with no impact on the footprint of the array. The consequence of SIW and metasurface technologies was improvement in the gain and radiation efficiency of the array. The proposed four orthogonal 4-element VAA covers the entire sub-5 GHz frequency range, and it radiates bidirectional in the azimuth plane and omni-directional in the elevation plane. Moreover, it is relatively easy to design and fabricate. The proposed VAA has dimensions of 0.96λ 0 × 0.96λ 0 × 0.0016λ 0 at mid-band frequency of 3 GHz. VAA has a measured gain of 25 dBi and radiates with 90% efficiency. The average isolation between the linear arrays constituting the virtual array is better than 27 dB. [ABSTRACT FROM AUTHOR]

We developed a theoretical formalism for the generation of optical vortices by phased arrays of atoms. Using the Jacobi–Anger expansion, we demonstrated the resulting field topology and determined the least number of individual atoms necessary for the generation of vortices with a given topological charge. Vector vortices were considered, taking into account both the spin and orbital angular momenta of electromagnetic fields. It was found for the vortex field that, in the far field limit, the spatial variation in spin-density matrix parameters—orientation and alignment—is independent of the distance to the radiation source. [ABSTRACT FROM AUTHOR]

A programmable metasurface antenna based on electrically tunable elements operating in 5G millimeter‐wave band, which has the features of low cost, easy manufacturing, low profile, easy integration with planar circuits, is proposed herein. The prototype consists of a 128‐element metasurface array, an 8‐channel beamforming chip as equal amplitude power divider networks, and a control network. Elements mounted with varactors to realize different states are controlled by DC bias signal from the back of a printed circuit board (PCB). By assigning different voltage values, array coding can be dynamically changed, thereby realizing beam steering. Both element dimensions and its location along substrate integrated waveguide (SIW) are optimized to better antenna performance. Experiment results show that the proposed metasurface can achieve not only the scanning range of ±70° for unidirectional beam in azimuth and ±40° in elevation but also ±50° for dual beam in azimuth. The whole prototype is fabricated based on PCB technologies, and good agreements among simulated and measured results are obtained. The proposed electrically tunable metasurface array is a good alternative to the traditional expensive phased array and has a great potential application prospect in radar and communication systems. [ABSTRACT FROM AUTHOR]

Diffraction gratings and photonic crystals are widely used to control light. However, their capabilities are less effective in the case of extreme ultraviolet (XUV) radiation due to the high absorption of the optical material in this frequency range. In this work, we study the possibility of enhancing the angular dispersion of XUV radiation due to scattering by plasma clusters whose dimensions are smaller than the incident radiation wavelength. An analytical model was developed using the plasma Drude dielectric function and the Mie scattering theory in the quasi-static approximation. The resonant parameters of the target for the tenth harmonic of the Ti:Sa-laser are determined, and a significant enhancement of the scattered field in this case compared to the laser one is shown. Under resonance conditions for one cluster, the diffraction of radiation by an array of such clusters is simulated using the CELES code. The results obtained show a significant enhancement of the scattered field in the resonance case for large angles corresponding to the theory of Bragg–Wulf diffraction, which makes it possible to control high harmonics of laser radiation in the XUV range using ionized cluster gas. [ABSTRACT FROM AUTHOR]

Free-space transmission of terahertz (THz) waves opens great opportunities for wireless applications including sensing and communication in the 6G era and beyond. Owing to their wider bandwidths and shorter wavelengths, the use of THz waves enhances information capacity and spatial resolution while downsizing aperture sizes compared to microwaves. On the other hand, the shorter wavelengths of THz waves can involve severe path loss. To compensate for the path loss, directional transmission based on beam steering is indispensable. In this article, we review the development of THz beam steering, which has been a longstanding challenge as well as the generation of high-power THz waves. While the use of active or passive phased arrays is the predominantly utilized approach to implement beam steering, other approaches based on variable diffractive structures and frequency dispersive structures offer low-cost alternatives. We also emphasize that application-driven system design approaches, in which THz beam steering is tightly coupled to signal processing, have been emerging to overcome hardware limitations. [ABSTRACT FROM AUTHOR]

Ultramassive multiple-input, multiple-output (MIMO) is one of the key enablers in the forthcoming 6G networks to provide high-speed data services by exploiting spatial diversity. In this article, we consider a new paradigm, termed holographic radio for ultramassive MIMO, where numerous tiny and inexpensive antenna elements are integrated to realize high directive gain with low hardware cost. We propose a practical way to enable holographic radio by a novel metasurface-based antenna, i.e., reconfigurable holographic surface (RHS). Specifically, RHSs incorporating densely packed tunable metamaterial elements are capable of holographic beamforming. Based on the working principle and hardware design of RHSs, we conducted full-wave analyses of RHSs and built an RHS-aided point-to-point communication platform supporting real-time data transmission. Both simulated and experimental results show that the RHS has great potential to achieve high directive gain with a limited size, thereby substantiating the feasibility of RHS-enabled holographic radio. Moreover, future research directions for RHS-enabled holographic radio are also discussed. [ABSTRACT FROM AUTHOR]

Featured Application: The significant feature of Wi-Fi 6 and beyond generations is a beamforming technology that allows the antenna arrays in a router or a client device (such as a tablet) to send and receive information over Wi-Fi in a desired direction. Conventionally, this is achieved using the commercially available phase shifters connected to the antennas. In contrast to commercially available phase shifters, the proposed novel phase shifters do not require additional electronics biasing circuitry, thus saving space and reducing the burden of additional power requirements at the Wi-Fi router. A linear phased array antenna excited with a novel composite right/left-handed (CRLH) phase shifters structure is proposed. The phase of the conventional CRLH transmission line is controlled with magnetically aligned micron-sized particles embedded inside the unit cell of the CRLH transmission line. The cascading of unit cells produces the desired phase shifts for the main beam scanning of the linear antenna array operating at a 5.5 GHz center frequency for Wi-Fi 6 applications. The proposed phase shifter design has a very low insertion loss (0.5–2 dB), excellent matching characteristics with the antenna array (less than −10 dB) and a small phase error (1–2 degrees). A 1 × 4 linear patch antenna phased array operating at a 5.5 GHz center frequency of the Wi-Fi 6 band is simulated using the Method of Moments (MoM) simulator platform. Then, the array is driven with the proposed novel CRLH phase shifters for the main beam at broadside and the main beam steered at 15- and 30-degree scan angles toward the desired users. For experimental validation, multiple unit cells of the proposed phase shifters are fabricated, and the 1 × 4 patch antenna array is fed with these fabricated unit cells of the phase shifters. The phased array radiation patterns are measured using an in-house fully calibrated anechoic chamber and were compared with simulated phased array patterns. The measured phased array patterns are in good agreement with the simulated patterns. As compared with commercially available phase shifters, the proposed novel CRLH phase shifters do not need external complex biasing circuitry, which is a major advantage in space constraint limitations at the router side of multi-user MIMO-OFDM systems. [ABSTRACT FROM AUTHOR]

This article presents the design method of a compact MEMS switched-line true-time delay line (TTDL) network over a wide frequency range extending from 2 to 42 GHz using TTDL units. The TTDL units, namely the cascading radio frequency micro-electromechanical system (RF MEMS) switches and GCPW, were employed in the proposed TTDL network to improve the delay-bandwidth product (DBW) while maintaining its compact size and low delay variation (DV). For comparison, a theoretical analysis of the RF MEMS switch was performed while observing the switch performance with various top electrodes. The MEMS TTDL network has a compact size of 5 mm × 5 mm, with a maximum delay of 200 ps and a minimum of 30 ps. The maximum insertion loss of 9 states is 10 dB, and the in/out return loss is better than 20 dB across 2-42 GHz. The group delay variations are within ±2.5% for all the delay states over the operating frequency range. To the best of our knowledge, the proposed TTDL network obtains the most control bits among the TTDL networks offered to date. [ABSTRACT FROM AUTHOR]

A broadband, unidirectional, phased array is proposed. Single antenna element of the prototyped array is a broadband windmill-like shaped antenna. Four elements of this antenna are fed by a power divider and are configured in a novel semicircular-shaped, angular-phased array. A phase difference of $\pi $ /4 was introduced by optimizing the angular path difference among four antenna elements in the array. Total 21.5% of size reduction is achieved by introducing angular-phased array in comparison with the conventional linear-phased array. The array of radius 65 mm is prototyped on the Rogers RO4232 substrate for the operating frequency range 9.35–42.89 GHz. The proposed array configuration can maintain an average gain of 8.54 dB and average radiation efficiency of 69.71% in the entire operating frequency range while exhibiting a peak gain of 11.86 dB. The presented array exhibits highly directional behavior in the endfire direction, with the 3-dB angular beamwidth in the range from 15.1° to 76.7°. To the best of the authors’ knowledge, any comparable state-of-art has not been reported yet in the literature that could provide such a large impedance bandwidth in sub-mmWave range. The proposed array may find its applications for future indoor and outdoor short-range communication networks. [ABSTRACT FROM AUTHOR]

Over the past decades, many radome designs to extend the angular scan range of phased-array antennas have been devised by utilizing dielectric materials and metamaterials. More recently, metasurface technology such as planar lenses and beam deflectors have been applied to phased arrays, enabling scan-angle enhancers to have a low profile. In this work, a physical Huygens’ metasurface (HMS) two-lens system for scan-angle doubling of a phased array is presented. For the HMS unit cells, the wire-loop topology is deployed to achieve high transmission for the required phase-angle shift. The proposed two-lens system is analyzed by full-wave simulations and experiments. The simulation results demonstrate that the scan angle doubles when the incident angle is below 15° in accordance to the design specification. Furthermore, the directivity degradation of the refracted beams by the two-HMS lenses is in good agreement with theory. Finally, a fabricated two-lens system with two $15\lambda $ long by $15\lambda $ wide metasurface lenses and a $16\times 16$ -element patch antenna array as a source is experimentally verified at ${\mathrm {10 \text {GHz}}}$ . The experimental results are in good agreement with the simulated results by showing angle-doubling performance with ±2° scan errors.

Distributed phased arrays based on unmanned aerial vehicle (UAV) swarm with small antenna elements on each micro-UAV are expected to achieve much better performance than the traditional phased arrays due to a large amount of swarm mobile individuals and deployment flexibility. To avoid the possible collisions of the flying UAVs, a large separation distance between UAVs is required, but grating lobes can appear when the array element spacing is larger than one-half wavelength. To solve this issue, array antennas with aperiodic element placement are normally used to mitigate the grating lobes, while suffering from a high collision risk for UAVs due to the reduced array element separation in the aperiodic array. This paper proposes a novel 3-D aperiodic array design by adding an additional degree of freedom in the optimization of array configuration. The sidelobe levels can be largely reduced from the planar periodic arrays. In addition, the collision risk for UAVs represented by the minimum separation distance between array elements can be largely decreased from the planar aperiodic arrays. This work provides a feasible strategy for the design and optimization of the UAV swarm-based phased arrays for practical applications.

We report on the first demonstration of dynamic beam steering using a scanning lens phased array. A scanning lens phased array relies on a combination of mechanical and electrical phase shifting to dynamically steer a high-gain beam beyond the grating-lobe free region using a sparse array. These two concepts have been demonstrated separately in the past, here we present, for the first time, a prototype demonstration where active mechanical and electrical phase shifting are combined. For this purpose, we have developed a sparse 4x1 scanning lens phased array at W-band (75-110 GHz) capable of beam steering a directive beam (>30 dBi) towards ± 20° with low grating lobe levels (around -10 dB). The lens array is fed by a waveguide-based leaky-wave feeding architecture that illuminates the lenses with high aperture efficiency over a wide bandwidth, which is required in the proposed scanning lens phased array architecture. The electrical phase shifting has been implemented using IQ-mixers around 15 GHz in combination with x6 multipliers to reach the W-band. The mechanical phase shifting relies on a piezo-electric motor, which is able to achieve displacements of the lens array of 6 mm with an accuracy of a few nanometers. The entire active array is calibrated over the air with an ad-hoc quasi-optical measurement setup. Resulting measurements show excellent agreement with the anticipated performance.

Low-profile foldable array antennas are becoming increasingly more important for a wide range of applications such as satellite communications and wearable electronic devices. The conventional arrays formed by patch-like antennas have been extensively studied on surfaces with a curvature but they have exhibited limited bandwidth and polarization performance. This study investigates a coupling enhanced crossed rings antenna array with two typical configurations for dual polarization, which inherently produces ultrawide bandwidth, dipole-like polarization characteristics and a fully curved array (FCA) eventually. The fractional bandwidth of the array is over 100% on a planar surface and expanded to approximately 140% on the curved surface. For the bent array of slant polarization, the beamwidth increases by over 20° compared to the planar array and cross polarization discrimination (XPD) maintains above 15 dB. The effects of curvature on the impedance matching and polarized radiation patterns for such arrays are investigated by measuring the performance of the fabricated prototype arrays. The results revealed that the tightly coupled crossed rings antenna array on a curved surface has a potential to form multiple beams on a limited aperture size through smaller subarrays which can yield ultrawide bandwidth due to concentrated mutual coupling mechanism. This characteristic is promising in applications where traditional flat panel arrays are difficult to implement such as in mobile stations, moving platforms and for satellite communication on-the-move.

A cavity-fed, dual-slot element and its 4-element linear array configurations for beam-steering applications at 28 GHz are described. The element cavity is formed from rectangular substrate integrated waveguide (SIW), perturbed at one of its corners to excite dual slots for increasing the impedance bandwidth. With a mobile terminal in mind, we look to both classical array principles and to the available theories for finite arrays with mutual coupling, to help guide the design. The impact of the finite ground-plane required to support the slot elements and array is investigated by simulation, including the impact on the patterns of using a cellphone chassis as a platform. A chassis-born 4-element (8 slots) configuration, suitable for beamforming in 28 GHz 5G networks is demonstrated for both linear polarizations. The simulation results are supported by pattern measurements of prototypes, a challenging task at 28 GHz.

To overcome the limited payload dedicated to onboard antennas for CubeSat/SmallSat applications, this paper presents a novel, foldable, dual-polarized Tightly Coupled Dipole Array (TCDA). In comparison to previous vertical feeds used for TCDAs, this array integrates a planar microstrip balun feed to enable foldability. The proposed array attains 5.4:1 (0.6-3.20 GHz) impedance bandwidth with VSWR < 3 at broadside and scans down to 45° at all azimuth planes. Notably, a substrate-integrated in-plane folding mechanism based on Lamina Emergent Torsion (LET) joints is employed to achieve foldability coupled with a simple fabrication process. The average simulated radiation efficiency was 95% across the band. A $5\,\, \times8$ prototype array was fabricated and tested to verify the finite array’s foldability, bandwidth, and gain performance. This prototype achieves 80% one-dimensional size reduction, yielding 60% overall volume reduction. Consequently, the array prototype can be folded and stowed in a compact volume of 1.4U (25 cm $ \times7.2$ cm $ \times9$ cm).

In this paper, we present an 8-bit precision passive true-time delay (TTD) operating at 5–11 GHz in 65-nm CMOS technology. To achieve a precision time delay control, the 8-bit TTD employs a 4-bit time delay circuitry that utilizes two LC delay networks in parallel to reduce the effects of the nonideal lumped components and layout imbalance of a conventional TTD. To design an 8-bit TTD, a 4-bit TTD with conventional LC networks was also used for the 5th bit to the 8th bit (MSB) time-delay for coarse delay control. The implemented 8-bit TTD circuit achieved a minimum delay of 1.56 ps and a maximum delay of 400 ps, demonstrating the smallest loss per delay among the recently reported state-of-the-art silicon-based TTDs without dissipating any DC power and with a chip area of $2.76\times 1.01$ mm2.