Transmitarray Research Articles

Metasurface Source Antenna Gain Improvement Using Simple Side Metal Structure.

As metasurfaces are in the spotlight, research is being conducted to incorporate them into transmitarray (TA) antennas. Among these, as an attempt to create a low-profile design, a patch antenna classified as low-gain can be utilized as an appropriate source antenna. However, for high efficiency of the TA, the gain of the source antenna must be fundamentally improved. For this, a simple side metal structure was applied to a metallic cross-type slot transmitarray. This acts as a resonant element and reflector by utilizing the electromagnetic wave radiated from the source antenna. The changes in the center frequency and gain due to the application of the side metal structure to the source antenna were analyzed. The gain of the source antenna was improved by a total of 4.63 dB. This is expected to be applied to create various source waves and to conduct future research on improving the gain in transmitarray antennas.

A microwave/millimeter-wave triple-band shared-aperture antenna integrating differentially-fed patch and transmitarray

This paper presents a microwave (MW)/millimeter-wave (MMW) triple-band shared-aperture antenna. It is implemented by integrating a differentially-fed patch (3.6 GHz) and a dual-band transmitarray (TA) (26 GHz and 39 GHz) through structure reuse. To realize an efficient integration, the patch antenna is evolved from a single-layer structure to a multi-layer one, with an extended ring-shaped patch added in each layer to obtain a proper transmitting surface (TS) size. For the TA, it adopts a unit cell (UC) consisting of two interleaved slots. By adjusting the lengths of the slots, independent dynamic phase shifts covering 360∘ can be attained for the 26 GHz and 39 GHz bands, respectively. To achieve an appropriate focal-to-diameter ratio (F/D) for the TA, a frequency selective surface (FSS) is employed to replace the ground plane of the patch antenna. Thanks to the spatial feeding architecture of the TA, the proposed antenna eliminates the need of complicated feeding network and features low feeding loss and high gain in the MMW bands. To validate the design idea, a prototype is fabricated and measured. The experimental results demonstrate that the proposed antenna can successfully operate in the three bands with peak gain of 7.6 dBi, 19.3 dBi and 19.5 dBi, respectively. In the 26 GHz and 39 GHz bands, beam scanning ranges of ±25∘ and ±13∘ can be obtained, respectively. The proposed antenna can be a promising candidate for 5G multi-band applications.

A 77 GHz Transmit Array for In-Package Automotive Radar Applications

A packaged transmit array (TA) antenna is designed for automotive radar applications operating at 77 GHz. The compact dimensions of the proposed configuration make it compatible with standard quad flat no-lead package (QFN) technology. The TA placed inside the package cover is used to focus the field radiated by a feed placed in the same package. The unit cell of the array is composed of two pairs of stacked patches separated by a central ground plane. A planar patch antenna surrounded by a mushroom-type EBG (Electromagnetic Band Gap) structure is used as the primary feed. An analytical approach is employed to evaluate the primary parameters of the suggested TA, including its directivity, gain and spillover efficiency. The final design has been refined using comprehensive full-wave simulations. The simulated gain is 14.2 dBi at 77 GHz, with a half-power beamwidth of 22°. This proposed setup is a strong contender for highly integrated mid-gain applications in the automotive sector.

Gain and mode purity filtering dual polarized OAM beam generation using cavity waveguide-based 3D transmitarray

A 3D transmitarray (TA) is proposed to generate dual-polarized orbital angular momentum (OAM) beams with gain and mode purity filtering responses. The TA units are realized by square cavity filters with the same passband and different orders and inner widths, resulting in different coupling cavity numbers. The evanescent modes in the coupling cavities will greatly decrease the propagation constant, thus generating a large phase variation. The square structure of the cavity filter makes it able to support dual-polarized wave propagation with the same phase delay and insert loss. Based on these transmission characteristics, eight different TA units are designed to realize a 3-bit phase gradient within the passband of 25.4–26.7 GHz. It should be emphasized that the dispersed transmission phase and magnitude of the eight TA units in the stopbands will deteriorate the purity of the OAM beam. Therefore, the gain and mode purity filtering responses can be realized simultaneously. In order to verify the performance of the proposed OAM TA design, a TA prototype with the mode number l = −1 is fabricated by 3D printing technology. The TA can realize the maximum gain of 25.9 dB in the passband, and the rejection level is below −15.0 dB within the main beam direction. The purities of dual-polarized OAM beams are over 0.5 in the passband, and the cross-polarization is below −16.5 dB. The advantages of the OAM TA, including gain-filtering and mode purity-filtering responses, dual-polarization, and high efficiency make it a promising solution for millimeter-wave OAM sensing and communication applications.

A Novel Approach to Remote Detection in Medical Radar Applications Using Flexible Transmit Array Lenses

A Novel Approach to Remote Detection in Medical Radar Applications Using Flexible Transmit Array Lenses

Flat-topped Beams using Phase Compensation based on Low-profile Transmitarray

This paper proposes a method to add an additional phase compensation to conventional phased arrays to achieve flat-topped beam forming, which can convert the spherical waves emitted by common conical horn antennas into cylindrical flat-topped beams, at the same time, there is also a certain power enhancement. A centrosymmetric unit composed of four layers of F4B and metal patches is designed. By changing the value of the parameters, a 360∘ phase change can be achieved, and it has the advantages of small size and low-profile. To validate the design concept, a prototype of the transmitarray (TA) was designed, fabricated, and measured by calculating the phase distribution of the front. The measurement results show that the designed TA can achieve flat-topped beams at 5.2GHz, the maximum gain is 1.15dB higher than that of the horn antenna, and the flat-topped range is about ±10∘. The results are in good agreement with the simulation within the test range.

FSS-inspired transmitarray for dynamic beamforming and gain control.

In this paper, we propose a concept of combining the methodology of phase coding modulation with frequency selective surface (FSS) inspired transmitarray (TA) to achieve the ability of dynamical beamforming and gain control in microwave regime. The TA element composed of five-layer stacked bandpass FSS units separated by small air gaps. Each FSS unit comprises a metallic octagon slot with a pair of varactor diodes loaded along the polarization direction. The elaborately designed feeding network makes it possible to modulate the transmission phase of each element. Different phase coding sequences are performed through changing the bias voltage configurations, then the radiation far field of the proposed TA can be tailored in real time. Dynamic beamforming and gain control under different encoding arrangements are exhibited to demonstrate the physical mechanism of electromagnetic (EM) manipulation with this method. The proposed strategy is verified by numerical simulations and experiment. This work adds new function for TA and can reshape its application prospect, such as reconfigurable beam emitter for multilink data transmission, long range point-to-point (PTP) wireless links and radio frequency energy harvesting.

Highly‐efficient optically transparent planarized transmit‐arrays using heterogeneous unit cells

AbstractTwo K‐band optically‐transparent (OT) transmit‐arrays (TAs) are proposed and demonstrated, which realize pencil beam and flat‐top beam, respectively. Based on the equivalent circuit analysis approach, the TA unit cells are designed using cascaded low‐loss cyclic olefin copolymer substrates and transparent conductor films with a 360° phase shifting and a total panel thickness of 0.46λ0. Phase compensation and an intersection approach are utilized to synthesize the pencil beam TA, with an aperture efficiency of 39.2%, and flat‐top beam TA, respectively. Both TAs are fabricated and characterized, showing a good agreement between the simulated and measured results. The pencil beam TA achieves a peak gain of 31.8 dBi with an 1‐dB gain bandwidth of 6.5%, while the flat‐top beam TA realizes a peak gain of 20.3 dBi with an 1.8‐dB beamwidth of 13°. The verified OT TAs can be useful candidates for communication and satellite applications in the 5G millimetre‐wave band.

Generalized Risley Prism for Beam-Steering Transmit Arrays With Reduced Grating Lobes

Generalized Risley Prism for Beam-Steering Transmit Arrays With Reduced Grating Lobes

A dual-band dual-polarized low-side-lobe transmitarray using independent amplitude and phase controllable elements

In this paper, a novel transmitarray (TA) element with independent control capability of amplitude and phase under dual-band dual-polarized operation is proposed. By changing the physical size of the TA element, the phase variation of the element can cover 360° at two bands. Moreover, the phase change of the frequency band is less than 30° when the phase of the other band is changed. Meanwhile, a higher maximal transmission amplitude can be maintained when varying the phase. Amplitude modulation is achieved by rotating the TA element. Utilizing the proposed TA element, a dual-band dual-linear polarization (LP) TA with low side lobe level (SLL) operating at 12.5 GHz and 14.25 GHz is designed. The SLL can be decreased by amplitude modulation of the elements. The measured peak gains of the proposed TA are 25.96 dBi and 25.89 dBi at 12.5 GHz and 14.25 GHz. In addition, the measured SLLs of the yoz/xoz planes are −22.4 dB/−22.4 dB and −22.5dB/−22.3 dB at 12.5 GHz and 14.25 GHz, respectively. The proposed TA shows good SLL performances and great application potential in satellite communication systems.

Electromagnetic Transmit Array With Optical Control for Beamforming

This proof-of-concept paper demonstrates the feasibility of using a slide projector to steer the beam of a transmit array by adding solar cells and varactor diodes to each unit cell. By irradiating each solar cell with the light of different intensities from a slide projector, the measured phase of the wave transmitted by the 4×4 transmit array shifts within 92° at 4.26 GHz, while the variation in magnitude is measured within 4 dB. Different light configurations are identified via a searching algorithm to achieve peak/null beamforming in a particular direction. The beam of the prototypical 4×4 transmit array can be shifted by ±24° in terms of the peaks and -30° to 36° in terms of the nulls. The concept of adding light modulation to the transmit array with a slide projector can provide update rates of 10s of milliseconds with control of brightness and color distributed over a large area of the array.

Wideband Transmit-Array Antenna Design With Dual-Layer Ultrathin Huygens’ Meta-Surface for Vehicular Sensing and Communication

This paper proposes a wideband high-gain transmit-array (TA) antenna for vehicular sensing and communication, which employs a dual-layer ultrathin Huygens' meta-surface (HMS). It consists of a 33 × 33 HMS unit cells-based TA, a feeder horn, and a three-dimensional printed fixture to hold them. Each HMS unit cell has two identical metal patterns (MPs) of two symmetrical U-shaped patches and one H-shaped patch, which are distributed on both surfaces of the ultrathin substrate. A pair of top U-shaped patches form the first single-wavelength loop mode, and another pair of bottom U-shaped patches forms the second single-wavelength loop mode. Due to the different phases of the incident waves on the top and bottom U-shaped patches, the two loop modes are generated at different frequencies. A third half-wavelength dipole mode is provided by the H-shaped patch. The three modes correspond to three different frequencies, forming a wide transmission frequency band. Three near-unity transmission peaks are yielded to ensure high and stable aperture efficiency (AE). As well, the transmission phase of the HMS unit cell varies with geometric dimensions, and five unit cell types are quantized to obtain 360° phase range with a low loss of less than 2.6 dB. To verify the design concept, a prototype is fabricated. Measurements show a 3-dB gain bandwidth of 17.9%, a maximum gain of 30.5 dBi at 26.2 GHz, and a high AE of 41.9%. It has unidirectional radiation pattern while reducing backlobe.

A W-Band High-Gain Bilayer Transmit-Array Antenna Employing Huygens’ Resonance

A special type of transmissive phase plate, named Huygens' metasurfaces (HMS), is capable of efficiently manipulating transmitted electromagnetic wavefronts with extremely low back-scattering. Here, in contrast to conventional planar multilayer lens arrays, a transmit-array (TA) antenna based on Huygens' resonance is proposed for high-gain applications at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band. The proposed meta-cell is comprised of a pair of parallel metallic strips on opposite sides of a single dielectric substrate connected by a pair of vias, and can independently control the electric and magnetic dipole responses and induce the desired Huygens' resonance. An equivalent circuit model (ECM) is used to describe its operation principle in detail. A full 360 degrees phase coverage and a high transmission amplitude can be obtained simultaneously using the proposed unit cell. To experimentally verify the proposed concept and design, a TA antenna is fabricated and tested. The Huygens' TA prototype exhibits good radiation performance. The measured peak gain of the TA prototype is 34.341 dBi at 87 GHz with an aperture efficiency of 45.7%, and the measured 3-dB gain bandwidth is from 79 to 90 GHz.

Analysis of transmitarray antenna elements using polarizability tensors

This paper presents an analytical approach to analyze transmitarray (TA) antenna elements using generalized boundary conditions (GBCs) and polarizability tensors. The proposed method analyzes multi-layer TA elements, which are composed of scatterers and dielectric substrates. The method combines an equivalent circuit model and network theory to evaluate total transmission matrix of multi-layer elements. Initially, each layer of scatterers is modeled by its collective polarizability tensor, which is calculated from individual polarizabilities of scatterers and their interactions. Next, analytical sheet admittance of layers is derived from their collective polarizabilities. Finally, total transmission matrix of multi-layer elements is calculated, taking into account the effect of resonant layers and dielectric spacers.This method determines the contribution of different items in the scattering properties of the elements separately, including the angle and polarization of the incident wave, the geometry and material of scatterers, and the array period. To validate the proposed model, several examples of multi-layer elements are analyzed, and the analytical results are compared with full-wave simulation results. A good agreement between them is achieved.The proposed approach is an efficient tool for the precise and fast design of transmitarray antennas, particularly where the effect of the incident angle needs to be considered.

A Wideband High-Efficiency Transmit-Reflect-Array Antenna for Bidirectional Radiations With Distinct Circular Polarizations Based on a Metasurface

In this communication, we present the modeling, design, and experiments of a wideband high-efficiency transmit-reflect-array (TRA) antenna with independent manipulations for transmitted and reflected beams with distinct circular polarizations working in the millimeter-waveband. A polarization-dependent full-space metasurface is designed to transmit the left-handed circularly-polarized (LCP) wave for a transmitarray (TA) operation, and at the same time to reflect the right-handed circularly-polarized (RCP) wave for a reflectarray (RA) operation. The TRA is then optimized with a rectangular shape for a high aperture efficiency (AE) based on a system-level analysis combining the characteristics of a Fermi feed antenna. The experimentally measured results are in good agreement with the simulated ones, achieving a peak gain of 22 dBi (21.5 dBi), a 1 dB gain bandwidth of 18.2% (24.6%), and a 3 dB axial ratio (AR) bandwidth of 38.6% (38.5%) for TA (RA) operation. A total AE as high as 61.2% is realized by comprehensively considering TA and RA operations. The design strategy and the well-performed TRA may find promising applications in wireless and satellite communication systems with bidirectional communication scenarios.

Design of Low-Profile Transmitarray Antennas With Wide Mechanical Beam Steering at Millimeter Waves

Mechanical beam steering using a single transmitarray (TA) can be a cost-effective solution for a high-gain antenna with wide-angle scanning. Elevation scanning can be achieved by a linear displacement of the feed in the focal plane parallel to the aperture of diameter D. When designing compact terminals with a short focal length F and with high gain, the aberrations caused by this mechanical movement become the main limiting factor for the maximum scanning range. This work presents a novel design method for devising the TA phase correction with an even distribution of these aberrations among all beam directions. A significant improvement in the scanning performance is achieved when compared with the conventional single-focus phase correction approach. To validate the proposed approach, we consider a TA design at the Ka-band (30 GHz) F/D <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cong ~0.34$ </tex-math></inline-formula> . A multifocal TA design was manufactured using 3-D printed unit cells. To highlight the proposed concept, the antenna configuration is stripped to the bare minimum: a perforated dielectric slab with in-plane mechanical movements in front of an open-ended standard waveguide used as feed. This antenna scans up to 50°, with a gain of 25 dBi at 30 GHz, 2.5 dB of scan loss, sidelobe level (SLL) <–10, and 1 dB bandwidth of 6.7%.

A shared-aperture transmissive/reflective bi-functional metasurface for both transmitarray and reflectarray

In this paper, a shared-aperture transmissive/reflective bi-functional metasurface is proposed. On metasurfaces, antisymmetric dipole pairs as transmissive elements and symmetric dipole pairs as reflective elements are interleaved in orthogonal polarization. By utilizing Huygens’ resonance, the metasurface can achieve near full phase coverage for orthogonally polarized transmitted and reflected wave. Then the bi-functional metasurface is used for the design of transmitarray (TA)/reflectarray (RA) bi-functional antenna. The measured results show that, for TA, the maximum gain is 30.26 dBi with antenna efficiency of 45.6 % and the 3-dB gain bandwidth is 26.3–29.3 GHz (10.79 %), and for RA, the maximum gain is 30.29 dBi with antenna efficiency of 45.7 % and the 3-dB gain bandwidth entirely covers the frequency region of 26–30 GHz. The bi-functional metasurface has important applications in the field of antenna engineering.

Generation of Mixed-OAM-Carrying Waves Using Huygens’ Metasurface for Mm-Wave Applications

Antennas that generate orbital angular momentum (OAM) have the potential to significantly enhance the channel capacity of upcoming wireless systems. This is because different OAM modes that are excited from a shared aperture are orthogonal, which means that each mode can carry a distinct stream of data. As a result, it is possible to transmit multiple data streams at the same time and frequency using a single OAM antenna system. To achieve this, there is a need to develop antennas that can create several OAM modes. This study employs an ultrathin dual-polarized Huygens' metasurface to design a transmit array (TA) that can generate mixed-OAM modes. Two concentrically-embedded TAs are used to excite the desired modes by achieving the required phase difference according to the coordinate position of each unit cell. The prototype of the TA, which operates at 28 GHz and has a size of 11 × 11 cm 2, generates mixed OAM modes of -1 and -2 using dual-band Huygens' metasurfaces. To the best of the authors' knowledge, this is the first time that such a low-profile and dual-polarized OAM carrying mixed vortex beams has been designed using TAs. The maximum gain of the structure is 16 dBi.

High Gain Millimeter-Wave Transmitarray Antenna Based on Asymmetric U-Shaped Metasurface Using Characteristic Mode Analysis

An asymmetric U-shaped millimeter-wave (MMW) metasurface (MS) transmitarray (TA) antenna is proposed based on characteristic mode analysis (CMA). The CMA of U-type unit shows two modes in the required frequency band and excites these two modes with a certain phase difference, so that the transmittance of the unit in the working band is greater than 0.8. The difference of lens unit is 360° by controlling the size change of the unit, and the transmission array is designed according to the phase distribution of the array. Through optimization simulation, the total size of the lens is 92.4 × 92.4 mm2, composed of 21 × 21 components and focal ratio of 0.85. The feed source is a SIW antenna, and then, the MS converts the quasispherical wave emitted from this feed source into a plane wave. The measured results show that the peak gain at 28 GHz is 22.3 dBi, the gain bandwidth at 3 dB is 5.8°, and the radiation efficiency is 81.6%. Due to the high gain and low-cost design, the proposed MS transmitarray antenna is suitable for MMW communication.

W-Band Low-Profile Transmit Array Based on Wideband Partially Reflecting Surface

This communication presents a wideband low profile transmit array (TA) with a small height-to-diameter (H/D) ratio of 0.285 working at a center frequency of 100 GHz, which consists of a waveguide feed source, a metal ground plane, a partially reflective surface (PRS), and a transmission surface (TS). A PRS with not only a positive reflection phase gradient, but also a negative transverse reflection magnitude gradient is designed above the ground plane to reduce the height as well as to broaden the bandwidth of the TA. The proposed TS is composed of eight unit cells (UCs) with a high transmission magnitude and phase differences of 45° in a broadband range. Four passive antenna prototypes with different beam directions are fabricated to validate the design concepts, and good agreements are obtained between the radiation patterns, gain curves, and return losses. The measured peak gain is 20.7 dBi with aperture efficiency (AE) of 10.5% at 99.5 GHz. A relative bandwidth of 15.2% is obtained within 3 dB gain variations, making it a promising candidate for sixth-generation (6G) wireless communication applications.