Transmitarray Research Articles

Dual‐band dual‐polarized transmitarray with independent control of polarization at each band

This article presents a dual-band dual-polarized transmitarray (TA) with independent control of polarization at each band. Five-layer cross dipoles and rectangular patches are utilized to control the transmission characteristics at Ku (13.5 GHz) and K (22 GHz) bands, respectively. Cross loops are used to improve the independence between two bands and transmission response. The phases can be controlled independently at both bands because of the band independence of the element. The vertical polarization and horizontal polarization phases at each band can also be controlled independently because of the polarization independence of the element. A TA with the specific beam direction for each polarization at each band is designed to verify the characteristics of the element. The TA antenna is fabricated and measured. The simulated results are consistent with the experimental results.

A Low-Profile and Beam-Steerable Transmitarray Antenna: Design, Fabrication, and Measurement [Antenna Applications Corner

This article describes the design, fabrication, and measurement of a low-profile and beam-steerable transmitarray (TA) antenna based on ray-folding principles. The proposed TA antenna consists of a planar feeding source, phase-shifting surfaces, and a metal plate as a reflector. The electromagnetic (EM) wave radiating from the planar feeding source would first be reflected by the metal plate and then propagate through the phase-shifting surfaces to achieve a focused beam in a specific direction. In this configuration, the profile of the proposed TA antenna is decreased to half compared with a conventional TA antenna.

Mechanically Reconfigurable, Beam-Scanning Reflectarray and Transmitarray Antennas: A Review

We review mechanically reconfigurable reflectarray (RA) and transmitarray (TA) antennas. We categorize the proposed approaches into three major groups followed by a hybrid category that is made up of a combination of the three major approaches. We discuss the examples in each category and compare their performance metrics including aperture efficiency, gain, bandwidth and scanning range and resolution. We also identify opportunities to build upon or extend these demonstrated approaches to realize further advances in antenna performance.

A Wideband Metal-Only Transmitarray With Two-Layer Configuration

This letter presents a novel wideband metal-only transmitarray (TA). Up to date, existing works on metal-only TAs use at least three layers spaced by air gaps. Compared to these designs, the presented TA has only two layers and can realize a full 360 phase shift with low insertion loss and wide bandwidth. The TA unit cell consists of two metal layers connected by a metal post and converts the linearly polarized incident wave to the orthogonal direction. This type of configuration increases the mechanical robustness of the TA surface and improves the alignment accuracy of the layers. Through mirroring the slots on the bottom layer, the electrical field of the transmitted wave is rotated by 180°, which is equivalent to a phase shift of 180°. Using this characteristic and simultaneously adjusting the lengths of the slots, a continuously 360° phase shift range is obtained. To verify this design concept, a prototype consisting of 256- unit cells was designed, fabricated, and measured. The experimental results show that the TA has 14.6% 1 dB gain bandwidth and 47.6% aperture efficiency at 8.5 GHz. The proposed TA has the advantages of wideband, no dielectric loss, and robust performance.

A high‐gain circular polarization beam scanning transmit array antenna

A high-gain circular polarization (CP) beam scanning antenna based on planar transmit array (TA) is proposed. The planar TA is implemented using rectangular patches and square rings, and it has different frequency responses to two orthogonal polarized incident waves owing to different phase distributions in x- and y-direction. The TA can convert a linearly polarized spherical incident wave into a circularly polarized transmitted plane wave. In addition, beam scanning is achieved by in-plane translation of the feed antenna. The procedure is demonstrated for high-gain beam steering implementation operating in CP at the Ku-band. Full-wave simulation results demonstrate that the designed antenna enables elevation beam scanning from −33.6° to +33.6°, with a peak gain of 26.4 dBi. Scanning loss is better than 5 dB and the axis ratio remains below 3 dB for the entire scanning range in the frequency band of 13.9–14.9 GHz. Moreover, a prototype is fabricated and the measured results have good agreement with the simulated results, which confirms the feasibility of using this technology to achieve a high-gain, CP, low-cost and low cross-polarization beam scanning antenna.

Wideband and Low-Profile Integrated Dual-Circularly-Polarized Transmit-Arrays Enabled by Antenna-Filter-Antenna Phase Shifting Cells

In this article, the theory, design, and demonstration of wideband and low-profile dual-circularly polarized (dual-CP) transmit arrays (TAs) are reported, which support independent beamforming for left-/right-handed CP waves. This is achieved by utilizing an antenna–filter–antenna configuration for the TA unit cells with a profile of only about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.11\lambda _{0}$ </tex-math></inline-formula> , which consists of receiving and transmitting stacked patches connected by two microstrip delay lines. By utilizing the phase delay lines and unit cell rotation, the dynamic phase and the Berry phase can be simultaneously exploited for providing continuous dual-CP transmissive phase compensation insensitive to the angle of incidence. The diffraction analysis of a linear gradient array of the proposed cells confirms its wideband performance of abnormal refraction. In addition, broadband CP planar feed arrays were designed and verified for functioning as low-profile feeds with symmetrical patterns for the TAs. As proof-of-concept examples, two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -band dual-CP TAs integrated with the planar feeds were synthesized, fabricated, and measured, possessing a total profile of about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.1\lambda _{0}$ </tex-math></inline-formula> . The two prototypes offer either symmetrical or asymmetrical dual-CP beams over a wide bandwidth. Their measured peak gain is higher than 22 dBic, while the joint <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11} &lt; -15$ </tex-math></inline-formula> dB, axial ratio < 2 dB, beam squinting <3°, and 2–dB gain bandwidth is wider than 12%. The design methodology and the proposed dual-CP TAs are useful in communication systems for space and wireless applications.

Multifunctional Tri-Band Dual-Polarized Antenna Combining Transmitarray and Reflectarray

A multifunctional tri-band antenna combining transmitarray (TA) and reflectarray (RA) is presented in this communication. Five-layer patches etched on three dielectric substrates with two air gaps are used as the unit cell. Cross dipoles inserted in cross slots control transmission characteristics at Ku-band (14 GHz). Double square rings on the top and bottom layers control reflection characteristics at K (21 GHz)- and Ka (30 GHz)-bands, respectively. The antenna has dual-polarized characteristics in each band. The phase shift range that can be obtained is 360° for 3 dB transmission magnitude at Ku-band and 0.15 dB reflection magnitude at K- and Ka-bands. The tri-band dual-polarized TA/RA antenna is designed, manufactured, and measured to verify the performance. The simulated results keep consistent with the measured ones. The measured results show that the TA has a peak gain of 23.8 dBi with an aperture efficiency of 40% at 14.25 GHz and 1 dB gain bandwidth of 6.5%. The RA has a peak gain of 28 dBi with an aperture efficiency of 44% at 21 GHz and 1 dB gain bandwidth of 7.3%, and has a peak gain of 31.5 dBi with an aperture efficiency of 47% at 30.5 GHz and 1 dB gain bandwidth of 7.1%.

Hybrid Numerical Methodology for Efficient Design and Optimization of Transmit-Array Antennas, X-Band Application

This paper presents a complete hybrid numerical methodology for the efficient design and optimization of large-scale Transmit-Array (TA) antennas for modern telecommunication applications. There are four main components to the proposed work and methodology: 1) the implementation through Python scripts of a hybrid scheme based on the Friis analytical formula for linking gain and phase of the primary source and elementary cells of the studied transmit-array; 2) the implementation of a Particle Swarm Optimizer (PSO) for efficient characterization of the optimal phase distribution on the in-plane lens maximizing the gain of the antenna and minimizing the side-lobe levels for multiple fed TA antennas; 3) the implementation of a full-wave Finite element and Interconnecting domain decomposition (FETI) for the final analysis of the TA radiating performance; 4) the design, optimization, fabrication and proof of concept of an X band transmit-array including the focal source. This work presents the main functionalities of the hybrid Python/CST tool associated with phase compensation PSO, FETI implementation for transmit-arrays and as an application of this numerical strategy, a new compact unit-cell operating in the X-band (thickness of 3.2 mm) able to easily generate Phase Rotations (PR) necessary for TAs with phase compensation on the aperture. The proposed unit-cell is a completely symmetric design including a metallic via interconnecting two identical square patches (including a circular hole in the center and a microstrip line) by crossing through a ground plane. A particle swarm optimization (PSO) routine is proposed as a way to quickly optimize the phase distribution of the transmit-array unit-cells. The optimization routine is tested through multiple sources and focal ratios, demonstrating a reduction of over 50% of the volume occupied by the antenna, while keeping a high gain (19.5 dBi) and overall good performance.

Beam-Steerable Passive Transmitarray Optimized Based on an Adjacent Algorithm

This paper presents a novel adjacent algorithm for the design of a beam-steerable passive transmitarray (TA) antenna. Even if the beam of a feed antenna is steering by varying the phase offset of the antenna array forming the feed antenna, the existing passive TA, which improves the gain only in the boresight direction, cannot improve the gain in all directions in which the beam is steering. To minimize the difference in the phase shift between different phase offsets by adjusting the reference phase instead of searching the entire space made up of the reference phase of each phase offset, an adjacent algorithm to change the reference phase with an adjacent phase that minimizes the objective function was adopted. This strategy improved the $O$ ( $\text{n}^{\mathrm {k-1}}$ ) algorithm to a linear algorithm of $O$ (n). It was also experimentally shown that optimization using the adjacent algorithm did not change the final result regardless of the initial value. Weighing the magnitude of the electric field (E field), the average optimized phase shift was obtained to determine the phase shift of the passive TA unit cell. Simulation of a TA consisting of an effective simple medium with a thickness of 2.5 mm reflecting the previously determined phase shift showed that the gain was improved by less than 1 dB when the phase offset was 0° and by more than 1 dB when the phase offset was 75°.

Dual-Band Quad-Polarized Transmitarray for 5G Mm-Wave Application

A dual-band quad-polarized transmitarray (TA) is designed in a common aperture operating at 25.9/39.8 GHz. Using narrow strip patches as cells, the 25.9 GHz cells are arranged in the ±45° direction, and the 39.8 GHz cells are arranged in the 0/90° direction in the formed square gap of the 25.9 GHz cells to realize a compact design with four polarization directions. In each band of 25.9/39.8 GHz, the proposed TA is dual-polarization designed. Measurements show that the expected beams can be achieved, and their 3 dB gain bandwidth covers almost all of the 5G bands n258 (24.25–27.5 GHz) and n260 (37–440 GHz). This TA has potential application value in 5G construction.

Natural reconstruction coordinates for imperfect TRASE MRI

TRansmit Array Spatial Encoding (TRASE) Magnetic Resonance Imaging (MRI) encodes image information in the Nuclear Magnetic Resonance (NMR) signal using spatially varying phases in a multiple spin-echo radio frequency (RF) pulse sequence. When the TRASE transmit coils are perfect, the spatial isophase RF contours produced are straight and orthogonal for a UXY TRASE sequence and the data produced fall into a well-understood k-space of spatial frequencies. When the TRASE coils are imperfect the spatial isophase RF contours will be non-orthogonal and/or curved. In that case the data produced by the TRASE sequence no longer falls into the traditional k-space. Here we show that the data fall into an alternative k-space relative to non-Cartesian coordinates in the image space that are naturally defined by the spatial isophase RF contours produced by the imperfect TRASE coils. With the construction of these natural image space coordinates, a direct image reconstruction transform may be defined. Simulated TRASE MRI cases with imperfect virtual transmit coils were computed and images reconstructed using the direct image reconstruction transform. The mathematical set-up here is a new one for MRI and may be amenable to further mathematical development as TRASE technology evolves.

A Broadband and FSS-Based Transmitarray Antenna for 5G Millimeter-Wave Applications

This letter describes the design of a broadband and FSS-based transmitarray (TA) antenna for 5G millimeter-wave applications. Two different elements are proposed to avoid the issues of the geometrical parameter resizing of the elements to obtain a 2 bit transmission phase of {−π, −π/2, 0, π/2} to achieve a TA antenna with wideband behaviors. Both of the two proposed elements show low insertion loss of below 1 dB from 24 to 38 GHz. Moreover, the two elements can achieve two sets of discrete transmission phases of {– π, 0} and {−π/2, π/2} without resizing their dimensions, respectively. A TA prototype based on the proposed two elements is designed and fabricated. The measured results agree very well with the simulated ones. The measured 1 and 3 dB gain bandwidth is 28.0–37.5 GHz (29.0%) and 25.1–39.1 GHz (43.7%), respectively. A peak aperture efficiency of 44.7% at 30 GHz is experimentally obtained with a realized gain of 26.1 dBi.

Transmit array resource allocation for radar and communication integration system

This paper considers a joint scheme of array resource allocation and transmit beamforming for radar and communication integration (RCI) capable of multiple target tracking and channel communication. The primary objective is to jointly minimize the Cramér–Rao lower bound (CRLB) of tracking filtering and Bit Error Rate (BER) of the communication subsystem. Firstly, two constrained optimization models are constructed and combined to obtain the RCI. Next, Majorization minimization (MM) is employed to convert the resulting optimization into a surrogate simpler problem, which is then solved by projected gradient descent (PGD). In addition, a transmit beampattern design problem is considered through optimizing the waveform covariance matrix under the shared and separated deployment. An appropriate beampattern is obtained based on array resource constraint, employing the PGD, while the peak power of the transmit beam is guaranteed for each target. Furthermore, iterative shrinkage-thresholding is applied as acceleration to the PGD in each algorithm. Numerical experiments are provided to illustrate the efficient performance of the joint array allocation and transmit beamforming for the RCI system, where the convergence of the algorithms is also confirmed.

A High-Efficiency Double-Layer Transmitarray Antenna Using Low-Loss Dual-Linearly Polarized Elements

A high-efficiency double-layer transmitarray (TA) operating at 14.25 GHz is proposed using low-loss dual-linearly polarized elements. Each element comprises only two layers of patches printed on a dielectric substrate and four vias. Cross dipoles and spiral dipoles with four L-shaped patches are used as the first and second unit cells, respectively. L-shaped patches are employed to increase the transmission magnitude. The phase shift range is 360° for a transmission magnitude of −1 dB. A square TA composed of 400 elements is designed, manufactured, and tested to verify the design. The simulated results are consistent with the experimental results. The experimental results show that the TA has a gain of 29.18 dBi at 14.25 GHz, an aperture efficiency of 60.3%, and a 1 dB gain bandwidth of 6.8%.

The effects of coupled B1 fields in B1 encoded TRASE MRI - A simulation study

Transmit Array Spatial Encoding (TRASE) is a novel MRI technique that encodes spatial information by introducing phase gradients in the transmit RF (B1) magnetic field. Since TRASE relies on the use of multiple RF fields (B1 fields with different phase gradients) for k-space traversal, a TRASE pulse sequence requires RF pulses that are produced by switching between the transmit coils (B1 fields). However, interactions among the transmit RF coils can cause un-driven coils to produce unwanted B1 fields that impair the spatial encoding. Therefore, TRASE is sensitive to B1 field perturbations arising from inductive coupling among the RF transmit coils and any B1 field isolation (coil decoupling) technique requires an understanding of the effects of the B1 field interactions. The purpose of this study was to investigate the effects of B1 field coupling using Bloch equation based simulations and to determine the acceptable level of B1 field interactions for 2D TRASE imaging. The simulations show that 2D TRASE MRI (using a 3-coil setup) displays ideal performance for pairwise coupling constant lower than k = 0.01 while having acceptable performance up to k = 0.1. This translates into S12 measurements of range ~(− 50 dB to −30 dB) required for successful 2D TRASE MRI in this study. This result is of crucial importance for designers of practical TRASE transmit array systems.

A Broadband Filter Transmitarray Based on Quasi-Yagi Antenna Element

A transmitarray (TA) antenna operating at X-band with band-pass filtering performance is presented. The proposed antenna is composed of a wideband TA and a filter feed antenna. Two quasi-Yagi antennas are connected as the unit cell of the proposed TA, leading to high transmission efficiency over a broadband range. By simply changing the length of the transmission lines, 360° phase shift is obtained. To verify this idea, a design with 16×26-unit cells is simulated and optimized, showing that approximately 14.5% 1-dB and 24.6% 3-dB gain bandwidths are achieved, respectively, with the peak gain of 23.1 dBi. Moreover, by employing the bandpass filter feed antenna, good bandpass filtering property is achieved, showing that the upper and lower out-of-band suppression in the 0.3GHz range can reach 27.3dB and 24.2dB, respectively, with the passband range from 9.6GHz to 11.9GHz.

A Dual-Polarized and High-Gain X-/Ka-Band Shared-Aperture Antenna With High Aperture Reuse Efficiency

This article describes a dual-polarized and high-gain shared-aperture antenna operating in Xand Ka-bands. The proposed shared-aperture antenna is implemented by combining a folded transmitarray (TA) antenna operating in Ka-band and a Fabry-Perot (FP) cavity antenna operating in X-band together. In this configuration, the shared aperture serves as a phase-shifting surface for the TA antenna and as a partially reflective surface for the FP antenna simultaneously. Since both of the two antennas radiate into free space through the same physical aperture, the aperture reuse efficiency of the proposed shared-aperture antenna is 100%. A four-layered, metallic double-ring structure is selected as the unit cell (UC) to implement the shared aperture to fulfill the aforementioned requirements. It is found that the frequency responses of the UC in Xand Ka-bands are highly independent, which can be controlled separately to facilitate the antenna design and optimization. Two dual-polarized patch antennas operating in Xand Ka-bands are utilized to enable a dual-polarized manner of the proposed shared-aperture antenna. The simulated results reveal that the proposed shared-aperture antenna has -10 dB bandwidth of 9.8-10.2 GHz and 26.5-29 GHz with the realized gain of 14.8 dBi (at 10 GHz) and 24.4 dBi (at 28 GHz) in two polarizations. All the simulations are experimentally verified.

A High-Performance Transmitarray Antenna with Thin Metasurface for 5G Communication Based on PSO (Particle Swarm Optimization).

A 5G metasurface (MS) transmitarray (TA) feed by compact-antenna array with the performance of high gain and side-lobe level (SLL) reduction is presented. The proposed MS has two identical metallic layers etched on both sides of the dielectric substrate and four fixed vias connecting two metallic layers that works at 28 GHz to increase the transmission phase shift range. The proposed planar TA consisting of unit cells with different dimensional information can simulate the function as an optical lens according to the Fermat’s principle, so the quasi-spherical wave emitted by the compact Potter horn antenna at the virtual focal point will transform to the quasi-plane wave by the phase-adjustments. Then, the particle swarm optimization (PSO) is introduced to optimize the phase distribution on the TA to decrease the SLL further. It is found that the optimized TA could achieve 27 dB gain at 28 GHz, 11.8% 3 dB gain bandwidth, −30 dB SLL, and aperture efficiency of 23% at the operating bandwidth of 27.5–29.5 GHz, which performs better than the nonoptimized one. The advanced particularities of this optimized TA including low cost, low profile, and easy to configure make it great potential in paving the way to 5G communication and radar system.

Novel one-bit digital coding broadband transmitarray antenna

In this paper, a novel broadband transmitarray (TA) design based on one-bit digital coding. The double-layer transmitarray element is composed of a notched square ring patches which is etched the upper layer of the dielectric substrate, and the lower layer is the same metal slit having the same shape as the notched square ring patch, but the notch direction is rotated by 180°. By changing the physical dimensions of the notched square ring element, a phase coverage of about 360° can be achieved. To realize the coding transmitarray, the phase compensation is fuzzified. Two kinds of elements with 0 and π phase responses to represent “0” and “1” elements for 1-bit digital coding are introduced. Theoretical rules of phase compensation fuzzified and a broadband transmitarray antenna are designed by coding unit cell. We design, manufacture and measure a digital coding transmitarray antenna by using the proposed element. The measured results show that the transmitarray has the 1-dB gain bandwidth of 25% (8.4 GHz - 10.8 GHz). The proposed digital coding transmitarray antenna has a wide gain bandwidth. The measured results agree with the simulated results well, which verifies the feasibility and correctness of the proposed structure.

Diffusion Imaging in the Post HCP Era

Diffusion imaging is a critical component in the pursuit of developing a better understanding of the human brain. Recent technical advances promise enabling the advancement in the quality of data that can be obtained. In this review the context for different approaches relative to the Human Connectome Project are compared. Significant new gains are anticipated from the use of high-performance head gradients. These gains can be particularly large when the high-performance gradients are employed together with ultrahigh magnetic fields. Transmit array designs are critical in realizing high accelerations in diffusion-weighted (d)MRI acquisitions, while maintaining large field of view (FOV) coverage, and several techniques for optimal signal-encoding are now available. Reconstruction and processing pipelines that precisely disentangle the acquired neuroanatomical information are established and provide the foundation for the application of deep learning in the advancement of dMRI for complex tissues. Level of Evidence: 3 Technical Efficacy Stage: Stage 3.