Zhi Ning Chen

• PhDs
• National University of Singapore at National University of Singapore

Simultaneously suppressing self-interference (SI), cross-talk interference (XI), and MIMO interference over a wide band presents significant challenges in a simultaneous transmit and receive (STAR) MIMO antenna. This paper presents a 2×2 STAR MIMO antenna that utilizes a usual stacked patch array while effectively suppressing all three types of int...

The miniaturized cage-like metacell is proposed for TE-TM balanced wide-angle transmission using the prior knowledge (PK)-guided generative deep learning (DL) method, enabling a low scan-loss metalens antenna. An initial metacell topology and pattern generation rules are proposed, guided by physical constraints and engineering experience, and effic...

An effective epsilon-mu-near-zero photonic crystal (EMNZPC) can be realized by degenerating three bands at the Г point with scattering from the high-permittivity dielectric. This paper presents a method to realize an EMNZPC by achieving triply degenerate bands at the Г point using gap metal rods in low-permittivity dielectric substrates. Open apert...

An efficient beamforming synthesis method is proposed for high-order-mode dipoles using artificial neural networks (ANN). Beamformed radiation pattern features and antenna parameters are set as the inputs and outputs of an ANN model to expedite antenna design by reducing the complexity and training volume of ANN. The flat-top beamforming of compres...

A method of mode conversion from the anti-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode to TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode is proposed to suppress the H-plane mutual coupling of slot-fed metasurface mosai...

In this paper, a conditional deep convolutional generative adversarial network (cDCGAN) for the metasurface (MTS) to reduce radar cross section (RCS) of the phased array is proposed. To reduce the calculation burden of collecting training data for cDCGAN, an equivalent circuit model is presented based on the mechanism of MTS. This method suppresses...

Wireless communications are rapidly advancing toward the next generation with much higher expectations for data rates, reliability, coverage, capacity, efficiency, connection, and latency, compared with existing systems. The antenna, as the most unique and innovative passive device, plays a crucial role in shaping the future of wireless communicati...

A henge-like metaring (HMR) is proposed for improving the radiation pattern roundness of monopole antennas off-center mounted on a finite ground by localizing the radiation from the monopole and suppressing the scattering by the ground. The improved patterns enhance uniform coverage of multiple-input and multiple-output (MIMO) systems. The study re...

In this paper, a compact wideband dual-polarized Luneburg lens antenna (LLA) with reduced anisotropy and improved impedance matching is proposed in Ka band with a wide 2D beamscanning capability. Based on transformation optics, the spherical Luneburg lens is compressed into a cylindrical one, while the merits of high gain, broad band, wide scanning...

An ultrathin dual polarization Huygens’ element (HE) is proposed based on a novel degeneracy method for electric and magnetic resonance modes. This HE exhibits a wider operation bandwidth and higher transmittance than the other hole-free dual-polarization lens antenna (LA) elements of similar thickness. By arranging three pairs of bilayer-dipole-pa...

In this paper, a scheme of outlier detection-aided supervised learning (ODASL) is proposed for analyzing the radiation pattern of a thinned cylindrical conformal array (TCCA), considering the impact of mutual coupling. The ODASL model has the advantage in speed improvement and memory consumption reduction, which enables a quick generation of the sy...

Most planar absorbers are designed under normal incidence, leading to a sharp decline in absorber performance under oblique incidence, especially when the incidence angle exceeds 30°. Three‐dimensional structured absorbers ensure the performance of the absorber under oblique incidence, but they lack practicality due to their complex processing and...

A novel integrated antenna supporting polarization and radiation beam reconfigurability is proposed for emerging millimeter-wave vehicular communication. To meet the reconfigurability requirement of the vehicular communication system, a compact shared-aperture two-dimentional leaky-wave antenna (LWA) is designed. The LWA is generated by the paralle...

A hat feed loaded with low-profile electromagnetic band gap (EBG) structure is proposed to reduce the radiation side lobe levels (SLLs) of reflector antennas. A mushroom shaped EBG structure is designed to suppress the surface currents along the external wall of the feeding waveguide distorting the primary radiation and elevating the SLLs of the re...

Cherenkov radiation (CR) is available for a wide variety of terahertz (THz) radiation sources, but its efficiency is deeply affected by intrinsic losses. We find that if the tilted angle (α) of anisotropic material and radiation angle (θ) meet the condition of θ + α = π/2, the intensity of radiation fields for the charged particle bunch (CPB) movin...

A characteristic mode (CM)-guided trust-region-based optimization technique for dual-band metantenna design is proposed. The technique automatically manipulates the CMs of a metantenna to achieve desired radiation patterns at desired frequency bands. Mode selection and tracking as the key steps of the technique are developed to track and detect des...

This communication proposes a reconfigurable reflectarray (RA) with decoupled right-/left-handed circularly polarized (RHCP/LHCP) 2-D beam steering. A simple-structured unit with mechanical reconfigurability is designed to achieve the 1 $\times $ 1-bit dual-circularly polarized (dual-CP) phase modulation, which enables the decoupled 2-D scanning...

Based on the Lorentz model of dispersive metamaterials (Lorentz dispersive metamaterials, in short), a method of generating single-mode dual-band operation of microwave patch antennas is presented. This method is inspired by the unique properties of Lorentz dispersive materials, which exhibit a higher refractive index at lower frequencies and a low...

Antennas have historically been the most common electromagnetic (EM) technology for wireless communication systems. Antenna as hardware is entirely dependent on the EM properties of the materials used, mostly related to the permittivity and permeability. In addition to natural materials, such as good conductors and low-loss dielectrics, metamateria...

A modified Jerusalem-cross absorber (MJCA) based on resistors is presented to minimize mutual coupling at two independent bands of a very compact quad-port multiple-input-multiple-output (MIMO) antenna. The double E-shaped radiating element features sectoral slots, enabling the antenna to function at two distinct frequencies: a lower band of 6.5 GH...

In this paper, a low-profile high-order-mode (HOM) antenna fed by an embedded L-shaped probe is proposed for high gain and broadband operation. Mode distribution in this low-profile cavity is studied. Three feeding structures, including substrate integrated waveguide, probe, and embedded probe, are discussed thoroughly regarding their effect on the...

This letter presents the design principle and experimental verification of a Ku‐band wideband low‐profile dual‐circularly polarized (dual‐CP) reflectarray (RA) with independent control of left‐/right‐handed circularly polarized (LHCP/RHCP) beams. Both the dynamic phase (DP) and Berry phase (BP) compensating methods are employed in the design of the...

A multiple tri-beam low scanning loss millimeter-wave (mmW) transmissive metasurface antenna for wide-angle coverage is proposed. The aperture phase distribution of the proposed metasurface is the superposition of the focusing phase and the periodic phase. Theoretical studies show that the size of the periodic phase element determines the direction...

In this letter, a flexible and ultra-thin uniplanar endfire antenna employing spoof surface plasmon polariton (SSPP) is proposed. The single-metal layered groundless structure is an inherent advantage of the SSPP. At the SSPP transmission line's end, a metallic strip is added asymmetrically for wideband radiation, resulting in an observed tilting o...

Recently, there has been growing interest in the use of metamaterial (MTM)-based lenses, also known as metalenses, as innovative antenna technology. Increasingly widespread applications of metalenses in modern microwave communication and sensing systems have been found, following the development of the first microwave artificial lens in the 1940s b...

A dual-polarized multi-resonant metantenna (MRMTA) is proposed for quasi-independent radiation and multiple in-band x -polarized scattering manipulations using characteristic mode analysis. The MRMTA unit cells in radiation and scattering modes have different resonance behaviors around meandering edges and inner slots, respectively. Moreover, tun...

A prior-knowledge-guided deep-learning-enabled (PK-DL) synthesis method is proposed to design the metacells with the full-range amplitude and phase control for suppressing the sidelobe levels of a metalens antenna. The PK-DL synthesis method is based on conditional deep convolutional generative adversarial network (cDCGAN). First, the metacells are...

This letter presents a low-profile, single-layer wide�band metamaterial-inspired circularly polarized (CP) multiple�input multiple-output (MIMO) antenna array. An 8×8 antenna array is manufactured on the Rogers RT/Duroid 5880 substrate with a partial ground plane. The dimensions of the proposed MIMO antenna array are 0.285λ × 0.11λ × 0.001λ at 28 G...

In order to design the wideband patch antenna, a hybrid method based on the artificial neural network (ANN) and the simulated annealing (SA) algorithm is proposed in this communication. The ANN is employed to describe the nonlinear relationship between the geometric parameters and the $S$ -parameters of the antenna. The ANN is trained by the data...

A millimeter-wave Yagi–Uda antenna comprising a third-order-mode driven dipole and a short reflector is proposed for gain enhancement. First, new design considerations for the director or reflector are proposed because of the reverse current along the third-order-mode driven dipole. Four schemes of the parasitic elements are analyzed when the drive...

A non-uniform compressed high-order mode dipole with suppressed sidelobe is proposed and investigated. The main performance characteristics, such as directivity, sidelobe, and radiation resistance of a 3^rd-order mode dipole with two independent compression coefficients are fully investigated. The investigation shows that enhanced directi...

An ultrathin and low-profile metalens antenna based on chain Huygens’ metasurface is proposed for 28-GHz band applications. The metasurface consists of an array series of modified dipoles etched onto a piece of dielectric substrate, and there is a half-unit dislocation along y-axis between these dipoles on top and bottom surfaces. Due to this geome...

A prephase synthesis method is proposed for side-lobe level (SLL) suppression of a 1-bit phase-only control metasurface under plane wave incidence. The array factor of the metasurface with N × N unit cells shows that controlling the number of prephases with varying values over the reflective surface can equivalently control the amplitude. Differe...

An anisotropic complementary metantenna (ACMA) is proposed for the integration of low sidelobe radiation and low in-band co-polarized (IBCP) scattering with the aid of characteristic mode analysis (CMA). With the guidance of CMA, the proposed ACMA evolving from a conventional metantenna (MTA) not only generates a coding phase distribution for low s...

A metasurface (MTS)-based reactive impedance surface (RIS) is proposed to load an eccentrically placed monopole above a ground plane for controllable wideband omnidirectional radiation. With the off-center placement, the radiation pattern of the monopole is not omnidirectional anymore, with ripples in the H-plane measured by un-roundness. The RIS i...

An interferometric phase transmitarray is proposed for spatial power combining to enhance the equivalent isotropic radiated power (EIRP) of the millimeter-wave (mmW) transmitters. The study shows that the multiple beams emitting from the ideal point sources located at different positions are combined into one beam to radiate in the boresight direct...

For some applications, the performance of the high-temperature superconducting (HTS) devices is limited by the fairly low impedance of the Josephson junction (JJ). Series JJ structure is a good choice to improve the impedance of the device so as to realize the impedance matching with the coupled antenna, in addition to solve saturation problem at t...

A flat-focal-plane dual-metasurface lens (dual-metalens) is presented to lower the scan loss and sidelobe level (SLL) of a metalens antenna. The dual-metalens consists of two metasurfaces with different phase shift distributions and focal ratios. This proposed metalens ensures that the focal points of 0° and 30° incident plane waves are on a flat p...

This article develops a broadband absorber by fully using the radiation features of monopole antennas for ultrawide-angle absorption application. A unit cell (UC) based on monopole antennas is proposed, and its working polarization is analyzed with the antenna reciprocity method and image theory. A wide-angle impedance matching layer is also introd...

Negative reflection and negative refraction are exotic phenomena that can be achieved by platforms such as double-negative metamaterial, hyperbolic metamaterial, and phase-discontinuity metasurface. Recently, natural biaxial van der Waals (vdW) materials, which support extremely anisotropic, low-loss, and highly confined polaritons from infrared to...

Negative reflection and negative refraction are exotic phenomena that can be achieved by platforms such as double-negative metamaterial, hyperbolic metamaterial, and phase-discontinuity metasurface. Recently, natural biaxial van der Waals (vdW) materials, which support extremely anisotropic, low-loss, and highly confined polaritons from infrared to...

This article, as part of the special issue on characteristic modes (CMs), updates the recent progress in developing advanced multiple antenna systems based on CM analysis (CMA). The multiple antennas include antenna arrays of multiple radiating elements fed by one single signal port, arrays of multiple antennas fed by multiple signal ports simultan...

The transformation-optics (TO) technique has been widely applied in the volume reduction of Luneburg lens (LL) in both optical and microwave regimes. However, it is found that the focus is usually not located on the surface of the transformed LL anymore after applying TO. The focus location shift results in a limited volume reduction, severe reflec...

A hemispherical Luneburg lens (LL) with the focal plane near lens surface is proposed using a transformation optics (TO) based metamaterial (MTM) lens (metalens) concept for wide-angle beamsteering applications. The TO technique has long been implemented to reduce the longitudinal dimension of an LL. However, the transformed lenses, usually having...

A prior-knowledge-guided deep-learning-enabled (PK-DL) synthesis method is proposed for enhancing the transmission bandwidth and phase-shift range of metacells used for the design of metalens antennas. The algorithm of conditional deep convolutional generative adversarial network is utilized in the proposed deep-learning method. Prior knowledge, in...

To optimize the reception and transmission in real-time changing links, phased array antennas have been increasingly investigated and applied in satellite applications. The phased array antenna technology intelligently combines multiple individual antenna elements to improve system performance in terms of gain enhancement, interference cancellation...

This letter presents a non-stationary 3D-GBSM vehicle to vehicle (V2V) channel model in tunnel environment based on massive multiple-input multiple-output (MIMO) antenna arrays. Instead of plane wavefront assumptions used in traditional MIMO systems, the proposed channel model considers spherical wavefront assumption for V2V communications. Firstly...

This brief presents a compact multiband multiple input multiple output (MIMO) antenna, where two robot-character-shaped patches are closely positioned on the top of the substrate for circular polarization. The dimensions of the proposed MIMO antenna are 0.34λ × 0.13λ × 0.01λ mm3 at 4 GHz and the distance between two symmetrical elements is 0.05λ mm...

A synthesis method of continuous source current on a high-order mode dipole is proposed to enhance gain and suppress sidelobe levels based on compression coefficients. First, a high-order mode dipole with the current distribution determined by designed compression coefficients is proposed to generate a typical continuous source. Then, a pattern syn...

A broadband coplanar feed patch antenna for 5G millimeter-wave (mmWave) applications is initially studied. To achieve good beam scanning/steering characteristics, the single patch antenna element design is applied to form a 1×4 antenna array with a gap distance (center-to-center) of 6 mm (about 0.5 $\lambda_{0}$ at 25 GHz) between two adjacent an...

A broadband polarization conversion metasurface (PCM) is proposed for reducing radar cross section (RCS) of antenna. The unit cell of the PCM consists of two pairs of tapered L-shaped strips, a layer of air, and a ground plane. The PCM unit achieves polarization rotation (PR) bandwidth of 117.2% with the polarization conversion ratio (PCR) of 90%....

A phased array loaded with a reactive impedance surface (RIS) is proposed for wideband wide-scanning performance. The mushroom-like RIS structure, etched on the same printed circuit board (PCB) of the antenna, is introduced as a superstrate over the antenna aperture. The reactance of the RIS structure compensates for the scan impedance variation of...

A double-layer metasurface is proposed to realize the low profile of a broadband dual-polarized antenna for cellular base-station applications. The proposed metasurface is formed by the two layers of printed metallic patch unit cells on either substrate surface to miniaturize the metasurface size and enhance design flexibility by regulating the ext...

A dual-band miniaturized linear-to-circular polarization converter (LCPC) metasurface with wideband and wide-angle axial ratio (AR) is proposed and demonstrated. The metasurface is formed with periodic arrays of unit cells. The unit cells consist of three metallic layers separated by two substrates. The top and bottom metallic layers contain the id...

A Huygens’ metasurface with unit cells of glide symmetric I-shape metal strips is proposed for a high efficiency metalens antenna. The proposed unit cell achieves more than 98.6% transmission amplitude with 360-degree phase shift coverage for dual polarization. The mechanism is presented by analyzing a unit cell with two dislocated I-shape metal st...

Amplitude and phase controllable metasurfaces are proposed to suppress the sidelobe levels (SLLs) of a metasurface lens (metalens). The amplitude-control metasurface is responsible for controlling the transmission amplitude with its unit cells’ phase shift variation less than ±10°. The phase-control metasurface is responsible for transferring the s...

A compact wideband and wide-scanning planar triangular-lattice phased array is proposed. The proposed element is a U-slot microstrip antenna surrounded by a substrate-integrated cavity (SIC) structure fed by a 50-Ω coaxial cable. The scan blindness is effectively shifted out of the operation band as the SIC structure obstructs the surface wave and...

Millimeter wave automotive radars are more and more popularly used to improve drivers' comfort and safety. High‐performance and cost‐effective radar sensor is always desired for the automotive industry. The antenna system is one of the key differentiating factors of an automotive radar sensor that defines the field of view and achievable angular ob...

Antenna development at mmW bands has many uniquely challenging issues wherein the measurement is one of the toughest ones because of the expensive testing setup, system limited dynamic range, complicated and tedious calibration, as well as measurement procedures. This chapter deals with the measurement issues of the mmW antennas operating from 60 G...

This chapter introduces the technology to suppress the surface wave losses caused by the thick and high‐permittivity dielectric substrate in mmW antennas. First, the mechanism of generation of surface wave losses is discussed. Then the method to suppress the surface waves is addressed with an example of patch antenna. After that, the planar and via...

Planar substrate integrated design of arrays with complicated feeding structures is a good option for high‐gain mmW antennas. By addressing the unique design challenges such as losses and fabrication tolerance, the design of the arrays at mmW bands needs the development of new radiating elements, array configuration, and feeding structures. As a re...

This chapter presents an overview of millimeter‐wave antennas and important related issues. In particular, the unique properties of millimeter‐wave propagation are addressed first. With a shorter wavelength, the millimeter‐waves suffer from higher pathloss and worse diffraction in its propagation compared with microwaves. The wavelength of the orde...

Mushroom structures are widely applied for not only composite right/left‐handed (CRLH) dispersion of guided waves but also electromagnetic band gap (EBG) characteristic of surface waves. This chapter introduces a metamaterial‐mushroom antenna array in LTCC for broadband and high‐gain operation at millimeter wave (mmW) bands. The unique working prin...