Millimeter-wave Band Research Articles

Experimental and numerical validation of tape-based metasurfaces in guiding high-frequency surface waves for efficient power transfer

We present an effective method for transmitting electromagnetic waves as surface waves with a tape-based metasurface design. This design incorporates silver square patches periodically patterned on an adhesive tape substrate. Specifically, our study proposes a strategy to enhance the efficiency of power transfer in high-frequency bands by guiding signals as surface waves rather than free-space waves. Both the numerical and experimental results validate the markedly enhanced efficiency in power transfer of high-frequency signals compared to that achieved with conventional methods, such as wireless power transfer and microstrips. Importantly, our metasurface design can be readily manufactured and tailored for various environments. Thus, our study contributes to designing power-efficient next-generation communication systems such as 6G and 7G, which leverage high-frequency signals in the millimeter-wave and terahertz bands.

23.5–27.5 GHz Band Doherty Power Amplifier Integrated Circuit Using 28 nm Bulk CMOS Process Based on Dynamic Power Dividing Network

This paper presents a Doherty power amplifier (DPA) integrated circuit (IC) designed to have enhanced gain, efficiency, and AM-AM characteristics through a dynamic power dividing technique, which can control the power dividing ratio according to the input power. Since this multi-purpose dynamic power dividing network also provides the phase offset and impedance matching at the interstage network needed for appropriate DPA operation, the active IC area could be reduced. To verify the proposed technique and its analysis, the DPA was implemented with a 28 nm bulk CMOS process for the fifth-generation (5G) new radio (NR) millimeter-wave frequency band of 23.5–27.5 GHz. The measured results showed a gain of 20.3–21.9 dB, saturated output power of 14.0–15.2 dBm, power added efficiency (PAE) of 22.8–26.7% at the peak power, and PAE of 14.6–17.6% at the 6 dB output power back-off (OBO).

Compact and Simple Antenna Inspection Testing Range for 5G Smartphones

Abstract Over-the-air (OTA) antenna performance evaluation in the millimeter-wave (mmWave) band often relies on Compact Antenna Test Range (CATR) systems, which require large reflectors and a substantial measurement range volume. Such setups are impractical for rapid testing in space-constrained environments such as antenna fault diagnosis in smartphone manufacturing facilities. This paper presents a novel design methodology for highly compact antenna inspection testing range utilizing offset parabolic reflectors specifically designed for 5G smartphones. The proposed design system employs three small offset parabolic reflectors configured to account for beam tilting caused by smartphone back covers, eliminating the need to physically reposition the smartphone during testing. By directing electromagnetic fields toward a fixed receiver antenna from multiple angles corresponding to different antenna module positions, the system streamlines the test procedure, significantly reducing measurement time and measurement range volume. The proposed antenna inspection testing range provides a cost-effective and efficient solution for 5G antenna fault diagnosis in manufacturing facilities, ensuring rapid and reliable inspection while minimizing space requirements on the production line.

Miniaturized tri-band integrated microwave and millimeter-wave MIMO antenna loaded with metamaterial for 5G IoT applications

This study presents a revolutionary tri-band combined microwave (MW) and millimeter wave (MMW) multiple-input-multiple-output (MIMO) antenna. The antenna is built on a Rogers RT-5880 substrate with dimensions of 32 × 32 × 1.6 mm³. This integration increased the isolation from 18 dB to 27 dB in the MW band and 28 dB–40 dB in the MMW band. The effective bandwidths for the MW and MMW bands were initially 3.3–3.7 GHz, 5.45–9.2 GHz, and 24–28 GHz, respectively. The MTM increased these bandwidths to 2.6–4.1 GHz, 5.3–11.3 GHz for the MW band, and 22.5–29.3 GHz for the MMW band. In addition, the realized gain increased significantly, from 1.5 dBi, 3.5 dBi, and 6.5 dBi to 4.5 dBi, 6.1 dBi, and 11 dBi at 3.5 GHz, 6.9 GHz, and 28 GHz. The antenna's overall efficiency increased by 10–12 % across all operational bandwidths. The suggested antenna has excellent diversity performance, with an envelope correlation coefficient of less than 0.0002, a diversity gain greater than 9.998, and a channel capacity loss of less than 0.12 bits/s/Hz. The proposed antenna addresses the increasing demand for IoT devices by efficiently supporting both MW and MMW frequency bands, offering high performance in wireless communication and modern infrastructures. The proposed design not only improves connectivity and efficiency in IoT devices but also supports the Sustainable Development Goals (SDGs) by contributing to the development of smart city infrastructure (SDG 11) and fostering innovation and sustainable industrial practices (SDG 9), thereby promoting sustainable development and industrial innovation.

Beam steerable MIMO antenna based on conformal passive reflective metasurface for 5G millimeter wave applications

A conformal reflective metasurface fed by a dual-band multiple-input multiple-output (MIMO) antenna is proposed for low-cost beam steering applications in 5G Millimeter-wave frequency bands. The beam steering is accomplished by selecting a specific port of MIMO antenna. Each MIMO port is associated with a beam that points in a different direction due to a conformal reflective metasurface. This novel conformal metasurface antenna design has the advantages of higher gain, lower cost, a simpler feeding source, and a lower profile when compared to traditional reflective metasurfaces using bulky horn antennas and phased arrays with complex feeding networks and phase shifters for beam steering. The proposed beam steering antenna consists of a compact five-element dual-band MIMO and a 32×32\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$32 \ imes 32$$\\end{document} unit-cell conformal dual-band reflective metasurface placed at the top of the MIMO antenna to obtain the beam steering capability as well as gain enhancement. The proposed reflective metasurface has a stable response under oblique incidence angles of up to 600\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$60^0$$\\end{document} at 24 GHz and 38 GHz and its symmetric, single-layer structure, ensures polarization insensitivity and stable response under conformal conditions. The presented MIMO antenna design is not only compact but also offers a wideband response effectively covering the desired 5G mm-wave frequency bands. The overall size of the MIMO antenna alone is 70 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 12 mm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {mm}^2$$\\end{document} with a maximum gain of 5.4 and 7.2 dB. It is further improved up to 13.1 and 14.2 dB at 24 and 38 GHz respectively, with a beam steering range of ś400\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$40^0$$\\end{document} by using a conformal reflective metasurface. Unlike the existing beam steering strategies, the suggested method is not only cost-effective but also increases the overall directivity and gain of the source MIMO antenna. The measured results agree with the simulated results, making it a potential candidate in the 5G and beyond beam steering applications.

A scalar method for measuring the reactive element in microwave and millimeter-wave bands

This paper introduces a novel scalar method to determine the value of reactive elements by only measuring the amplitude value of the reflection coefficient. The methodology is illustrated using a Smith Chart, integrating reactive elements in series or parallel with a standard resistance element, and deriving a corresponding equation. Simulation results closely align with theoretical predictions. This approach extends beyond reactive elements, applying universally to π/T-network circuits. It obviates the need for Vector Network Analyzers (VNA) in measurement, reduces equipment requirements, and holds substantial importance for measuring diverse types of reactive microwave elements.

Advanced Metamaterial-Integrated Dipole Array Antenna for Enhanced Gain in 5G Millimeter-Wave Bands

A metamaterial-based non-uniform dipole array antenna is presented for high gain 5G millimeter-wave applications with a wideband characteristic. Initially, a non-uniform dipole array is designed on a 0.202 mm thick Rogers RO4003C substrate, offering a wide operating bandwidth ranging from 23.1 GHz to 44.8 GHz. The dipole array antenna emits unidirectional end-fire radiation with a maximum gain of 8.1 dBi and an average gain of 6.7 dBi. Subsequently, to achieve high gain performance, a 5 × 7 metamaterial structure is designed in the direction of the antenna radiation. The implemented metamaterial structure is optimized for the operating frequency, enhancing the directivity of the antenna radiation and resulting in a gain increment of more than 3 dBi compared to the dipole array alone. The developed metamaterial-integrated dipole array antenna offers an operating bandwidth (S11 < −10 dB) of more than 21 GHz (63.92%), ranging from 23.1 GHz to 44.8 GHz, covering the most commonly used 5G millimeter-wave frequency bands (n257, n258, n259, n260, and n261). Furthermore, the presented antenna yields a stable high gain with a peak gain of 11.21 dBi and a good radiation efficiency of more than 64%. The proposed antenna is an excellent option for millimeter-wave 5G systems due to its overall properties, particularly its high gain and end-fire radiation characteristics, combined with a wide operating bandwidth.

A 2–36 GHz CMOS LNA with π-Network-Based wideband interstage matching technique for software-defined radio systems

With the advance in wireless communication, next-generation software-defined radio (SDR) systems require transceivers to operate in both sub-6GHz and millimeter-wave (mmWave) band and support multiple standards. However, bridging sub-6GHz frequencies with millimeter-wave bands exceeding 30 GHz remains a challenge for conventional wideband LNAs. To surmount this, a 2–36 GHz CMOS low-noise amplifier (LNA) designed for SDR systems is introduced in this paper. An innovative wideband input matching network capable of spanning both frequency domains is proposed. The methodology effectively mitigates the impact of vast parasitic capacitances, achieving wideband input matching against Electrostatic Discharge (ESD) and on-chip decoupling capacitor parasitic. In addition, a π-network-based wideband interstage matching technique is adopted to extend bandwidth of gain. A tri-stage prototype of the proposed LNA, designed using a 40-nm CMOS process, is designed to validate our design strategies. The post-simulation outcomes reveal a peak gain of 14 dB with a -3dB bandwidth ranging from 2 to 36 GHz, equating to a fractional bandwidth of 178 %. The Noise Figure (NF) is commendably uniform across the frequency spectrum, stabilizing at 5 dB. Furthermore, the third-order input intercept point (IIP3) is −4.2dBm to -3dBm across the bandwidth. The performance is achieved with a power of 19.4 mW and within a core area of 0.1 mm2.

A 132–170 GHz high-gain driving amplifier utilizing asymmetric broadside coupled line in 40-nm CMOS

This paper presents a driving amplifier (DA) utilizing the proposed asymmetric broadside coupled line. In contrast to conventional coupled line, the balun devised with proposed asymmetric coupled line and enhanced wideband balance compensation technique is utilized, thereby achieving wideband impedance matching and mitigating insertion loss. Additionally, the utilization of the lossy over-neutralization technique substantially enhances the power gain of amplifiers operating in the upper millimeter-wave band (150 GHz–300 GHz). The DA is fabricated utilizing a 40-nm CMOS process without aluminum layers. The fabricated amplifier demonstrates a compact total area of 0.135 mm2 (0.031 λ2), with a core area of 0.027 mm2 (0.0061 λ2). It achieves a high gain of 19.4 dB, high power of 11.05 dBm, and high power-added efficiency (PAE) of 11.05% at 160 GHz. Moreover, both the 3-dB power gain bandwidth and the 3-dB saturated power bandwidth extend from 132 GHz to 170 GHz, covering a bandwidth of 38 GHz. This configuration underscores the robust performance of the DA in the upper millimeter-wave band.

A Low-Profile Dual-Band Millimeter Wave Patch Antenna for High-Speed Wearable and Biomedical Applications

This paper presents a low-profile, dual-band patch antenna designed for the mmWave frequency range. The antenna, fed by a microstrip line, is fabricated on a thin, flexible substrate (Rogers 3003) with dimensions of 12 × 3 × 0.25 mm³. The radiating patch includes two circular slots, enabling dual-band operation at 28 GHz and 38 GHz. Key performance metrics, including realized gain, efficiency, and radiation patterns, are analyzed across these frequency bands, with measured results compared to simulations performed using CST Microwave Studio. Furthermore, the antenna's parameters are evaluated in a bent configuration, demonstrating its suitability for wearable applications. The study also assesses the antenna's impact on human tissues, calculating average SAR values of 0.914 W/Kg and 1.140 W/Kg at 28 GHz, and 0.720 W/Kg and 1.360 W/Kg at 38 GHz, for 1/10 gm tissue. Furthermore, the link margin is calculated to verify effective wireless communication over distances up to 80 meters. This antenna effectively covers key millimeter-wave frequency bands, making it ideal for high-speed 5G and biomedical applications.

Performance Evaluation of Reconfigurable Intelligent Surfaces-Assisted Millimeter-Wave Network Using Stochastic Geometry-Based Model

Millimeter-wave (mm-wave) bands have received significant attention due to their large bandwidth and high frequency. However, mm-wave signals experience high attenuation primarily as a result of their high directivity and vulnerability to blockage, leading to non-line-of-sight (NLOS) conditions and signal outages. Buildings, structures, and natural obstacles can cause signal blockage, which increases connection challenges and creates coverage gaps. A reconfigurable intelligent surface (RIS) is a potential technique that can improve the coverage of mm-wave networks by intelligently reconfiguring the wireless propagation environment. RIS offers novel solutions to blockage issues by passively reflecting and rerouting mm-wave signals in desired directions. This paper presents a simulation-based evaluation of the signal-to-interference ratio coverage probability in RIS-assisted mm-wave networks based on stochastic geometry. We will use random shape theory to represent the blockages within the network. Furthermore, the impact of increasing the density of RIS and the number of reflective elements on network performance will be examined. The results show that RIS can enhance network coverage and decrease the effects of blockages, with considerable increases in coverage probability when compared to networks without RISs.

A planar-structured circularly polarized single-layer MIMO antenna for wideband millimetre-wave applications

This paper presents a planar multiple-input-multiple-output (MIMO) antenna with dual circular polarization (CP) and a simple geometry for millimetre-wave band. The proposed design is featuring a fully grounded coplanar waveguide (CPW) and a systematically perturbed feedline radiator. The symmetry of the electric field is disrupted using varying stub sizes and offsets between the stubs, resulting in wideband operation and circularly polarized waves. Following full optimization of the physical parameters, the numerical design is validate experimentally. The results indicate that the proposed antenna design achieves a −10 dB impedance bandwidth from 24.6 GHz to 32.1 GHz, with an axial ratio (AR) of 3 dB or less from 26 GHz to 31.8 GHz. The peak realized gain is 10.3 dBic, with steady broadside radiation. The envelope correlation coefficient (ECC) is 0.01, and the diversity gain is 10 dB across the operating band. The planar structure and the wideband performance of the proposed design makes it suitable for application necessitating fix beam applications in the mm-wave band.

Transmissive invisibility cloak using phase gradient metasurfaces

Different from the reflective approach of the carpet cloak designed to conceal surface irregularities on highly reflective surfaces, the transmission invisibility cloak, often capable of achieving perfect invisibility, operates within a transmission geometry. In this configuration, the cloaking mechanism ensures that an object neither reflects nor refracts incoming waves in free space, presenting opportunities for more versatile applications, though with the requirement for intricate designs. This paper introduces a novel methodology for designing a transmissive invisibility cloak, employing a simplified combination structure of two phase-gradient metasurfaces based on the generalized Snell’s law. Initially, we designed a highly transparent metasurface for the millimeter-wave band to yield diverse phase gradients. We confirmed the effectiveness of this metasurface through the observation of abnormal refraction. Then, through a deliberate arrangement of these phase gradients, we construct a transmissive invisibility cloak that guides electromagnetic waves around the cloaked region. Simulations and experimental measurements conducted under plane-wave conditions demonstrate the cloak’s effectiveness and practical applicability. The ensuing comparative investigations of results among free space, uncloaked objects, and cloaked objects validate the expected cloaking effect, offering valuable insights into the design and functionality of transmissive invisibility cloaks.

Experimental results of multiplexing transmission of 256-QAM 5G NR signal with control signal by SCM over 20-km analog RoF link

Analog radio over fiber is attracting interest as a low-cost solution for high-frequency band distributed antenna systems (DAS). DAS demands the beamforming, TDD timing switching, and CLK synchronization of each distributed antenna section (or remote radio unit (RRU)), but as the number of optical carriers used for RRU control increases, the result is an undesirable increase in RRU complexity. In this paper, we propose and demonstrate a wireless system that can simultaneously transmit, via a single optical carrier, an analog main signal and a control signal (beamforming, TDD, and CLK signals) by subcarrier multiplexing (SCM). Simulations show that the signal quality degradation caused by nonlinearities in the optical modulator during SCM transmission can be avoided by properly designing the input power balance between the analog main signal and the control signal. We also conducted experiments on the downlink transmission of 256 QAM-modulated 5G NR signals by connecting a CS-RRU pair with a 20-km SMF. According to our OTA evaluation using a millimeter-wave band antenna, the EVM value was about 3.41%, which satisfies the 3GPP specification. In addition, control signals were found to be demodulated successfully.

Wideband meander-line-antipodal-vivaldi slot-antenna for millimeter-wave applications

An antipodal Vivaldi monopole radiator is employed in an innovative wideband planar slotted meander antenna. A quarter-wave microstrip feed is coupled to the antenna for a ground reflector plane over a meander line with five right and left antipodal Vivaldi (RLAV) slots on either side and a series of Z, inverted U and inverted Z-shaped turns. The FR4 substrate with a relative permittivity of 4.4 and modest dimensions of 50 × 20 × 1.6 mm3 is used to implement the proposed antenna. A 17.39% fractional bandwidth of -29.10dB (S11 <-10dB), an average radiation efficiency of 73%, and a gain of 6.7dBi at the central frequency of 28GHz. The outcomes of using RLAV arms at the centre of the meander structure enhance the antenna’s performance validated using the high-frequency structural software Ansys 2022R1, which is a finite element method (FEM) tool. The measured results indicate that the bandwidth enhancement has been fine-tuned for use in the 5G millimetre wave band in the Frequency Range 2 (FR2) n261 frequencies, the 3rd generation partnership project (3GPP) band n257, and the Federal Communications Commission’s (5G) high-band spectrum (25-30GHz).

Millimeter-Wave Band Electro-Optical Imaging System Using Polarization CMOS Image Sensor and Amplified Optical Local Oscillator Source.

In this study, we developed and demonstrated a millimeter-wave electric field imaging system using an electro-optic crystal and a highly sensitive polarization measurement technique using a polarization image sensor, which was fabricated using a 0.35-µm standard CMOS process. The polarization image sensor was equipped with differential amplifiers that amplified the difference between the 0° and 90° pixels. With the amplifier, the signal-to-noise ratio at low incident light levels was improved. Also, an optical modulator and a semiconductor optical amplifier were used to generate an optical local oscillator (LO) signal with a high modulation accuracy and sufficient optical intensity. By combining the amplified LO signal and a highly sensitive polarization imaging system, we successfully performed millimeter-wave electric field imaging with a spatial resolution of 30×60 µm at a rate of 1 FPS, corresponding to 2400 pixels/s.

Multilayer-laminated optically transparent 300-GHz-band transmissive beamforming metasurface for wireless communication

A 300-GHz-band transmission-type multilayer metasurface beamformer based on a Jerusalem cross geometry is presented. A metamaterial cell with a continuous 2π phase variation for the radius change was designed and used in the fabrication of a reference device and three types of beamforming devices. The beamforming metasurface devices achieved steering angles of θ = 18°, θ = 30°, and θ = 38°, which were in good agreement with simulated results. A broadband operation in a 40 GHz band, from 280 GHz to 320 GHz was evaluated, showing only minor frequency dependence of the beamforming angles. The design and fabrication methodology can be applied to various types of metasurface devices, such as circular and fan lenses, beamformers, polarization switches, and so on for millimeter-wave frequency bands that are considered to be used in future 6 G wireless network systems.

Enhanced 2-port MIMO antenna with composite two-step metasurface for 77 GHz Vehicle-to-Everything applications

The article presents a 2-port multiple-input multiple-output (MIMO) antenna array designed for millimeter-wave band operation, specifically optimized for Vehicle-to-Everything (V2X) applications. To enhance performance, a novel approach employing two types of metasurfaces on a single plate is utilized. The first metasurface, based on a loop structure, aims to improve the frequency bandwidth, while the second metasurface, utilizing a composite right/left-handed (CRLH) design, focuses on reducing mutual coupling. These two steps result in an improved frequency bandwidth exceeding 45% and a decreased structure width of about 50% compared to other designs. Notably, the compact nature of these metasurfaces, measuring approximately 32 × 3 mm2, is a significant feature that reduces manufacturing costs. The arrayed antenna, with 20 series elements, is suitable for medium-range radar in V2X applications, although our method is generally applicable to other ranges. Additionally, the radiation pattern exhibits a 40-degree beam rotation within the frequency bandwidth, making it well-suited for V2X applications. The results demonstrate impressive diversity performance, with a consistent maximum gain of 16 dB across the entire frequency bandwidth of approximately 68 GHz to 82 GHz, representing an 18.2% coverage.

Ultra-Compact 4-Port MIMO Antenna with Defected Ground Structure and SAR Analysis for 28/38 GHz 5G Mobile Devices

To tackle the challenge of keeping 5G mobile devices compact while supporting millimeter-wave bands, we've created an ultra-compact 4-port dual-band MIMO antenna with a defected ground structure (DGS). This design minimizes mutual coupling and covers a broad frequency range. Built on a Rogers TMM4 substrate with dimensions of 17.76×17.76 mm2, the antenna includes four planar patch antennas positioned perpendicularly at the corners. Each antenna operates at 28/38 GHz and features a rectangular patch with four rectangular slots and a full ground plane. The patches are separated by 0.5 λo, with the DGS further reducing mutual coupling. Both simulations and measurements indicate a significant reduction in mutual coupling (−39 to −60 dB), improving ECC, TARC, MEG, and DG. Time-domain and SAR analyses confirm the antenna's efficiency and its suitability for 5G devices.

Exquisite regulation of LZ-BaM/PPy composites for compatible absorption across centimeter-wave and millimeter-wave bands

The increasing complexity of the electromagnetic environment necessitates materials to exhibit superior microwave absorption performance for multitudinous bands. However, reaching satisfactory compatibility for absorption across centimeter-wave and millimeter-wave bands still remains a formidable challenge. In this work, a composite composed of Polypyrrole (PPy) and La3+-Zr4+ co-doped barium ferrite (LZ-BaM) is elaborately designed to address the issue facing us today. By exquisitely regulating the chemical composition, absorption peaks ascribed to different integral orders of interference can appear simultaneously in millimeter-wave and centimeter-wave bands. Ultimately, the as-prepared LZ-BaM/PPy composite reveals an efficient absorption (RL < −5 dB, absorptivity of 68.37 %), covering the centimeter-wave band of 8∼17 GHz and millimeter-wave band of 27∼40+ GHz concurrently under a matching thickness of 2.4 mm. This study thus offers valuable insights for the development of high-efficient absorbers across multiple frequency bands.