Transmitarray Antenna Research Articles

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%.

An ultra-thin high-efficiency plasmonic metalens with symmetric split ring transmitarray metasurfaces

Metasurface lenses (or metalenses) have aroused great attentions and efforts in the community of metamaterials or metasurfaces due to its ultrathin device dimension and superior focusing performances. High-efficiency transmissive metalenses with an ultra-thin device thickness are an important aspect especially in the low frequency by using plasmonic transmitarray antennas. In this paper, an ultra-thin plasmonic metalens with only 0.1λ (λ is working wavelength, the aperture size is 7λ) device thickness is designed by changing the radius of the proposed symmetric complementary split ring resonator antenna metasurfaces. Thanks to its high transmittance and large phase shift of the plasmonic meta-atoms, the designed metalens achieves both high transmissive efficiency of 80% and high focusing efficiency of 50% on the focal plane of F = 4.6λ in the simulations. The designed ultra-thin plasmonic metalens has a moderate large numerical aperture of 0.67 (NA = 0.67). In order to verify its high working efficiency of the proposed plasmonic metalens, a sample is also fabricated and a much higher focusing efficiency of 65% is realized in the measurements. The influence of the open angles of the symmetric split ring transmitarray metasurface on the focusing performances such as working efficiency and NA of the designed metalens is also studied and analyzed finally, which can add new degree of freedoms to optimize its focusing performance. The presented studies can facilitate the development of high-efficiency metalenses in the low frequency and have significant potential applications in high-resolution microwave imaging, high-gain metalens antennas and others.

Reconfigurable Folded Transmitarray Antenna With Low-Profile Based on Metasurfaces

A reconfigurable folded transmitarray antenna (RFTA) with fully planar structure is presented in this letter. It consists of an electronically reconfigurable metasurface and a polarization rotating metasurface (PRMS). A pair of PIN diode switches is integrated on the reconfigurable meta-atom to realize the 1-bit transmission phase manipulating, and a patch antenna is integrated on the center of the PRMS to feed the RFTA. Through twice reflecting, polarization rotating, and transmission phase compensation, the spherical wave from the feed is transformed into the scannable pencil-shaped beam. Meanwhile, the antenna profile is reduced to about 1/3 compared to the traditional reconfigurable transmitarray antenna (RTA). The RFTA prototype with 12 × 12 elements is designed, fabricated, and measured. Experimental results show that the gain of 13.4 dBi at 5.8 GHz is obtained and the two-dimensional beam scanning angle covers ±60°. This work significantly reduces the profile of traditional RTA, making it a promising candidate for the wireless communication system with limited space.

Broadband circularly polarized folded transmitarray antenna based on polarization conversion metasurfaces

In this communication, a novel design of compact and low-profile broadband circularly polarized folded transmitarray antenna (CPFTA) is reported. A broadband linear-to-circular polarization conversion metasurface (PCM) with multi-mode operation is initially developed as the sub-reflector, to reflect the y-polarized waves and transmit x-polarized waves into right-handed circularly polarized waves. Additionally, by rotating the circularly polarized transmitters, geometric phase can be exploited for phase compensation. Then, a linear-to-linear PCM with high efficiency is designed as the main reflector. As verification, a CPFTA integrated with a broadband planar feed source and the proposed high-efficiency PCMs at X band is designed, fabricated, and experimentally characterized. The measured results are in good accordance with the simulated ones, revealing a −10 dB impedance bandwidth of 28.7%, a 3 dB gain bandwidth of 22.9%, and a 3 dB axial ratio bandwidth of 31.9%. Meanwhile, the achieved peak gain is 25.2 dBi at 10.35 GHz with a maximum aperture efficiency of 28.3%. Combining the advantages of broadband operation, flat gain, and ease of integration, the proposed CPFTA is an attractive candidate for modern wireless communications.

Design and analysis of microstrip transceiver array antennas with the function to suppress beam deflection for 77 GHz automotive radar

A microstrip transceiver array antenna with high beam pointing accuracy is designed for automotive radar. Considering the influence of the lossy conductor on the excitation current, the beam deflection problem formed by the passive microstrip series-feed linear array is analyzed and solved. Compared with the traditional microstrip series-feed linear array, the microstrip series feeder array designed in this paper has good beam pointing accuracy. A power divider based on substrate-integrated waveguide (SIW) and microstrip line (MSL) with Chebyshev amplitude distribution(applied to the transmit array antenna) and binomial amplitude distribution(applied to the receive array antenna), respectively, is designed as the feeding network of the linear array. The fabrication and measurement of the prototype transceiver array antenna are completed to verify its beam directivity. The simulation and measurement results show that the E-plane main beam of the transceiver array antenna radiation pattern has good pointing accuracy, which makes the detection accuracy of the automotive radar significantly improved.

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.

A Wideband Circularly Polarized Transmitarray Antenna for Millimeter-Wave Applications

A wideband circularly polarized (CP) transmitarray antenna (TA) is presented for millimeter-wave applications. First, a wideband CP TA element is designed by combining two wideband antennas, one of which is a linearly polarized (LP) magnetoelectric (ME)-dipole antenna, and the other is a CP antenna with orthogonal electric-dipole mode and patch mode. Both of the two antennas are fed by a probe from the center of the unit cell; thus, the CP antenna can be rotated freely to realize the required phase shift. Then, a CP TA with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15\times 15$ </tex-math></inline-formula> elements is designed based on the unit cell proposed here. To excite the proposed TA, a fully metallic ME-dipole-based antenna array featuring wide operating bandwidth with a low profile and ease for assembling is used as the source antenna. Finally, by integrating the CP TA with the source antenna, a prototyped millimeter-wave CP TA is designed, fabricated, and measured. Experimental results show that the gain of the proposed CP TA is up to 25.6 dBic at 33 GHz with a peak aperture efficiency of 44%. The 3 dB gain bandwidth is 33.8%, and the axial ratio (AR) is smaller than 2 dB within a bandwidth of 37.5% from 26 to 38 GHz.

다기능 투과배열 안테나 단위셀 소형화 설계를 위한 360° 반사형 축소형 아날로그 위상 천이기 설계

This study compares the designs of one-stage and two-stage reflection-type phase shifters for miniaturized S-band multi-functional transmit-array antennas. Both phase shifters have areas smaller than 0.2 λ0×0.4 λ0, which is less than half of the conventional unit cell size of 0.5λ λ0×0.5 λ0, and both phase shifters have a phase shifting range of more than 360°. The one-stage phase shifter requires a miniaturized hybrid coupler, 1/4 wavelength transmission line, and additional elements to implement a wide phase shifting range; hence, the phase shifter has a non-uniform insertion loss distribution and a peak insertion loss of 4.3 dB. The two-stage phase shifter outperformed the one-stage phase shifter; it had a relatively uniform insertion loss distribution of 2.5 dB because of its simple circuit structure.

Reflect–Transmit-Array Antenna With Independent Dual Circularly Polarized Beam Control

In this letter, we propose a dual circularly polarized reflect–transmit-array (RTA) antenna with independent beam control. It can transmit left-hand circularly polarized (LHCP) wave as transmitarray antenna and reflect right-hand circularly polarized (RHCP) wave as reflectarray antenna at 8.7–10.2 GHz. In addition, 360° phase shift for each circularly polarized wave can be achieved by rotating the top and bottom patches. A 20 × 20-unit cell RTA is designed, fabricated, and measured. For the LHCP radiation, the measured results show that the 3 dB gain bandwidth and axial ratio (AR) bandwidth are 13.7% (8.8–10.1 GHz) and 15.9% (8.7–10.2 GHz), respectively. For the RHCP radiation, the measured 3 dB gain bandwidth and AR bandwidth are 11.4% (9.1–10.2 GHz) and 12.6% (8.9–10.1 GHz). The peak aperture efficiencies for LHCP and RHCP radiations are 45.5% at 9.2 GHz and 41.8% at 9.6 GHz, respectively.

Performance Improvement of Mechanically Beam-Steerable Transmitarray Antennas by Using Offset Unifocal Phase Symmetry

This communication presents the concept of offset unifocal phase symmetry to improve the performance (gain, gain roll-off, sidelobe level, etc.,) of mechanically beam-steerable transmitarray (TA) antennas. The phase shifts are initially determined from an offset feed source to make the corresponding TA antenna radiate a tilted beam with high gain. The phase shifts are asymmetric and can be broadly divided into dominant and ordinary phase shifts with respect to the offset feed source. By mirroring the dominant phase shifts to make the phase shifts symmetric, it can enable symmetric radiation beams for symmetric offset feed sources and improve phase error. When the offset feed source is moving inward to steer the main beam, the phase error of the phase-shifting surface with respect to the feed source starts to occur, while the electric-field spillover/illumination from the feed source is improved, which can maintain the gains of scanning beams. To verify the validity of the concept, the performance of a beam-steerable TA antenna enabled by the offset unifocal phase symmetry has been simulated and compared with the counterparts of unifocal and bifocal beam-steerable TA antennas. The measured results agree well with the simulated ones, revealing that the beam-steerable TA antenna enabled by the offset unifocal phase symmetry can maintain realized gains of scanning beams, suppress sidelobe levels, and reduce gain roll-off within the beam-scanning coverage. The offset unifocal phase symmetry, in principle, is a generalized approach and applicable to reflectarray antennas to improve the beam-steerable performance as well.

Far-Field Wireless Power Transfer for the Internet of Things

A complete end-to-end far-field wireless power transfer (WPT) is proposed and studied in this paper for the application of the Internet of Things (IoT) at the industrial, scientific, and medical (ISM) band of 2.4 GHz. The radiative WPT has achieved a remarkable attraction for the capability to transfer power in the long range. We propose two approaches. In the first approach, a 2×4 microstrip patch transmitter antenna array with a high gain and a narrow beamwidth is proposed that is rotated toward the IoT device using a small stepper motor. The performance of the rectifier in the receiving circuit was separately analyzed, and 17.54% efficiency was achieved with a load of 0.6 kΩ for the circuit, while the input power was 10 dBm. The overall system test was performed and the targeted result was investigated considering the distance between the transmitter and the receiver, and an input radio frequency (RF) power of 5 dBm to 15 dBm at 2.4 GHz. The second approach uses a 1×4 transmitter antenna array fed through a Butler matrix to provide four individual beams with a 22.5∘ angular separation, and 90∘ total angular coverage. The goal was to focus the power into four angular locations and to reduce the power waste in other directions. A mobile app was developed to control the direction of the beam. A system efficiency of as much as 19% was measured for an input RF power of 0 dBm and a resistive load of 62 kΩ.

A Method for Transmitarray Antenna Profile Reduction Based on Ray Tracing Principle

In this letter, a method named double phase-compensation is first proposed to drastically reduce the profile of traditional transmitarray antenna (TA) based on ray tracing principle. Previously, the folded transmitarray antenna (FTA) has realized the profile reduction to 1/3. It is known that there is an urgent need for more compact antenna nowadays. If the FTA's profile is further reduced, the focus-to-diameter ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> ) ratio should be decreased which will result in obvious aperture efficiency reduction. To further reduce the FTA's profile with unchanged <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> for keeping high efficiency, the extra phase compensation is innovatively added on the FTA's reflector. Hence the TA's profile can be reduced to lower than 1/3 and be flexibly adjusted as needed. Three FTA models are designed for comparison and demonstration. The simulation and experimental results indicate that the extra phase compensation successfully alleviates the efficiency drop caused by directly reducing the profile of FTA. Significantly, the method provides an efficient approach to further improve the compactness of antenna system and is very meaningful for TA miniaturization.

A One-bit Transmit Phased Array with Spatial Excitation for Sub-6 GHz Wireless Systems

Introduction. Due to the increasing number of users, growing rates of data transmission, and rapid advancement of the Internet of Things, the parameter of channel capacity is acquiring greater importance in modern communication systems. In wireless communication systems, capacity limitation occurs due to a low signal-to-noise ratio, one reason for which consists in high losses associated with the propagation of electromagnetic waves. These losses can be compensated using high-gain antenna systems, such as metasurfaces, transmitarrays, or reflectarrays.Aim. Development and research of a one-bit transmit phased antenna array with spatial excitation for use in wireless communication networks across sub-6 GHz frequencies. The issues of reducing the insertion losses associated with the cell geometry and control components are discussed. Account is taken of the parasitic parameters of p–i–ndiodes used as control elements for phase adjustment in a unit cell. Methods for suppressing cross-polarization in a unit cell with the purpose of reducing insertion losses are studied.Materials and methods. The characteristics of unit cells in a transmit antenna array were studied by numerical electrodynamic modeling in the CST Microwave Studio computer-aided design system. The obtained results were confirmed by an experimental study of samples.Results. A unique design of a unit cell comprising the main element of a transmitarray was proposed. On its basis, a transmitarray was designed and manufactured, whose measurements proved the level of insertion losses to be lower than 1.5 dB in the operating frequency band of 210 MHz (3.6 %). The level of cross-polarization was found to be lower than 24 dB, and the gain attenuation did not exceed 2.5 dB in the range of beam deflection from 45° to -45°.Conclusion. The design simplicity, low losses, and acceptable cross-polarization levels of the developed one-bit transmit phased antenna array with spatial excitation confirm its feasibility for modern communication systems.

Signal processing in passive radar with multi-user MIMO-OFDM signal

In this paper, we propose a signal processing method in passive radar using the multi-user (MU) multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) signal as the illuminator of opportunity. The MU-MIMO-OFDM modulation is adopted in the fifth-generation (5G) communication. We consider the scenario where multiple mobile users share the same time–frequency resources but separate spatially in different beams formed a prior by the MU-MIMO transmitter antenna array, which is a quite general case in realistic 5G communication. A beam-by-beam matched filter is proposed for weak target sensing. Interference suppression is also discussed. The interference in this scenario is more complicated than that in the traditional passive radar. In the MU-MIMO communication system, the base station (BS) transmits multiple signals to different beam regions simultaneously for the communication between the BS and mobile users. For a specific beam region where the radar receiver is located, the interference consists of not only the direct and multipath interference (DMI) of the signal transmitted by the BS to this beam region, but also the inter-user interference (IUI) from the other beam regions. The DMI and IUI degrade the weak target detection capability significantly. In this paper, we propose a suppression method for jointly eliminating the DMI and IUI. Simulations verify the effectiveness of these methods.

Wide‐angle beam‐scanning transmitarray antenna with low scan loss

AbstractIn this letter, a mechanical beam‐scanning transmitarray antenna with a wide scan coverage is presented. A wide‐band element is designed to provide a linear transmission phase shift with a low transmission loss, which comprises a double‐arrow and two orthogonal grid polarizers printed on two substrates. Then, a dual‐beam phase matching method is introduced to reduce the scan loss. To verify the design, a 437‐element transmitarray with a circular aperture (D = 150 mm) is simulated, fabricated, and measured. The measured results indicate that the transmitarray antenna achieves a ±40° scan coverage while keeping a low scan loss (&lt;1.8 dB). The side lobe levels keep lower than −15 dB in the entire scanning range. Moreover, a 1‐dB gain bandwidth of 21% (14–17.2 GHz) can be achieved in terms of boresight radiation, and the measured peak gain is 23.5 dBi at 15 GHz.

Phase controllable FSR design and its application into a high-gain transmitarray antenna with a low radar cross-section

In this study, a high-gain transmitarray antenna (TAA) is proposed to achieve a low radar cross-section (RCS) with polarization-insensitive characteristic. Initially, an anisotropic frequency selective rasorber (FSR) structure is constructed by a detailed analysis of the current distributions and parameter adjustments. Hence, manipulations of absorption and transmission are achieved, along with covering a transmission phase cycle by rotating the element at 90°. Then, employing a phase-controllable FSR and focal length optimization, a low-RCS and high-gain TAA is presented. For the radiation case, the proposed antenna has a pencil pattern with a peak gain of 21.8 dBi. The F/D ratio is low when a wide-beam feed is utilized. At scattering state, in-band and out-of-band 6 dB RCS reductions are realized ranging from 7.6 to 10.4 GHz and 11.6–12.4 GHz compared to the reference TA. Moreover, its bistatic RCS is reduced in approximately ±90° of angular space under normal incidence. The effectiveness of the proposed design is verified by experiments.

Circularly Polarized Double-Folded Transmitarray Antenna Based on Receiver-Transmitter Metasurface

In this communication, a circularly polarized (CP) double-folded transmitarray antenna (DFTA) is proposed and experimentally verified for the first time in the open literature. It is designed based on a receiver–transmitter metasurface (RTMS) and a polarization rotating (PR) metasurface (MS). A linearly polarized (LP) patch antenna is integrated on the RTMS instead of a horn antenna to feed the DFTA. Through double-folded reflecting, twice PR, LP wave receiving, CP wave transmitting, and transmission phase manipulating, the LP spherical wave from the feed is transformed into the high-gain pencil-shaped CP beam. The strategies innovatively break the restriction that the previous folded reflectarray (FRA) and folded transmitarray (FTA) antennas are only LP. Moreover, the double-folded design further reduces the antenna profile to about 1/4 of the focal length. The simulation and experiment results are in good agreement, which exhibits a peak gain of 21.8 dBic at 9.8 GHz and a maximum aperture efficiency of 40%. Meanwhile, the DFTA obtains a −1 dB gain bandwidth of 6% (9.6–10.2 GHz), in which the axial ratio is lower than 1.5 dB.

Circular-Polarization-Selective Metasurface and Its Applications to Transmit-Reflect-Array Antenna and Bidirectional Antenna

In this article, a cascaded metasurface (MS) with circular-polarization-selective properties is proposed, which can achieve high reflection for left-handed circular polarization (LCP) and high transmission for right-handed circular polarization (RCP). Such MS, constructed by cascading two kinds of MS sheets, can conduct decoupled geometric phase modulations for the LCP reflection channel and RCP transmission channel by respectively rotating the two elements in the two MS sheets. In order to show its practical applications, first, the proposed MS is applied to design a reconfigurable circularly polarized (CP) transmit-reflect-array antenna (TRA) that can be switched between a high-gain LCP transmitarray antenna and a high-gain LCP reflectarray antenna (RA) dependent on the polarization state of the feed antenna. The simulated results validate its function-switchable and high-gain characteristics. Second, a CP bidirectional antenna is designed utilizing the proposed MS and validated by a fabricated prototype with good agreement between the measured and simulated performances. The results indicate that the joint bandwidth (BW) for both forward and backward aperture efficiencies larger than 20% and axial ratios smaller than 3 dB is about 16% (9.4–11 GHz), across which the antenna realizes bidirectional high-gain and high-purity LCP radiations.

Transmitarray Antenna for Conical Beam Scanning

Conventional transmitarray antennas are designed to produce a directional pattern with the beam peak in a single direction when the feed is placed at a distinct location. A real-life application requiring conical beam scanning necessitates the development of antennas with patterns that sweep out a cone in space through successive excitation of feeds placed at multiple locations along the body of the revolution ring focus. In this communication, we propose transmitarrays as an antenna solution that can achieve the conical beam sweep. Compared to the previously reported transmitarrays, the development of an off-axis-fed transmitarray for conical beam scanning requires significant advancements regarding the synthesis and optimization of the off-axis-fed transmitarray. A novel synthesis algorithm is presented based on the optimization of the feed location and a modified transmitarray phase compensation. To validate the approach, an 18 cm transmitarray with a thickness of 0.8 cm operating at 13.4 GHz is designed, simulated, prototyped, and measured. Predictions obtained by full-wave simulations agree well with the measured results. The conical beam scanning capability of the transmitarray is demonstrated through measurements taken with the feed placed at five locations within the ring focus.

Hybrid phase compensation method for ultrathin folded transmitarray antenna

The folded transmitarray antenna (FTA) attracts a lot of attention for its low-profile, high gain beam as well as easy fabrication. By adding a reflector to conventional transmitarray antenna (TA), multi-folded reflection is obtained and the profile between the feed and transmitarray is reduced to about 1/3 compared with that of TA, while it does not satisfy the requirement of integration property for modern communication systems. In this work, to further reduce the profile of FTA and keep the optimal focus-to-diameter ratio, a general strategy is firstly proposed by hybridizing the reflection and transmission phase compensation for the FTA design. Owing to the extra reflection phase compensation, the FTA’s profile can be further reduced and can be set arbitrarily. As an example, an ultrathin FTA with a profile reduction to 1/4.2 is designed based on the proposed method, and another two conventional FTAs are used for comparison. The simulation and test results indicate that the hybrid design method provides an effective strategy to improve the compactness of antenna system.