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Metasurfaces have promising potential to revolutionize a variety of photonic and electronic device technologies. However, metasurfaces that can simultaneously and independently control all electromagnetics (EM) waves' properties, including amplitude, phase, frequency, polarization, and momentum, with high integrability and programmability, are challenging and have not been successfully attempted. Here, we propose and demonstrate a microwave universal metasurface antenna (UMA) capable of dynamically, simultaneously, independently, and precisely manipulating all the constitutive properties of EM waves in a software-defined manner. Our UMA further facilitates the spatial- and time-varying wave properties, leading to more complicated waveform generation, beamforming, and direct information manipulations. In particular, the UMA can directly generate the modulated waveforms carrying digital information that can fundamentally simplify the architecture of information transmitter systems. The proposed UMA with unparalleled EM wave and information manipulation capabilities will spark a surge of applications from next-generation wireless systems, cognitive sensing, and imaging to quantum optics and quantum information science. The authors show a universal metasurface antenna capable of simultaneously and independently controlling all five fundamental properties of electromagnetic waves, including amplitude, phase, frequency, polarization, and momentum. [ABSTRACT FROM AUTHOR]

This article introduces a novel near-field focus (NFF) lens antenna with a three-dimensional (3-D) focus-steering capability operating at terahertz (THz) frequencies. The antenna consists of a pair of thin discrete dielectric lenses (DDLs) placed above a stationary feed horn. First, we demonstrate that the DDL doublet’s in- plane synchronous counter-rotation and co- rotation could scan its focus radially and azimuthally, respectively. A multi-focus synthesis method that compensates the required transmission phases at multi-focus points is developed to further improve its NFF-steering performance. The DDL-based antenna can realize 3-D focus-scanning using a combination of rotation and linear translation mechanisms. The 3-D printing is adopted to fabricate the THz antenna to simplify the manufacturing process and reduce the cost. Both numerical and experimental results demonstrate that the 15 mm-diameter antenna prototype can scan its focus in a 3-D cylindrical space with a diameter of 29 mm and a length of 8 mm at 300 GHz. The proposed 3-D focus-scanning antenna with a large field of view (FoV) of 72° will open new avenues for fast 3-D THz imaging applications. [ABSTRACT FROM AUTHOR]

This article introduces a transmitarray antenna presenting excellent filtering and dual-polarization properties. Conventional transmitarrays resort to multilayered frequency-selective surfaces (FSSs) for filtering responses. In contrast, we propose a planar dual-polarized filtering antenna as an illumination source to enable a filtering transmitarray. The V-band dual-polarized filtering antenna is excited by a substrate integrated waveguide (SIW) feeding structure. By a novel trisection feed and a well-design radiating element, up to four radiation nulls are produced, leading to an excellent filtering response validated with experimental results. Subsequently, the antenna is employed to illuminate a phase-shifting surface (PSS), achieving outstanding filtering response, stable dual-polarization characteristics, low profile, and ease of integration. The proposed antenna and transmitarray demonstrate significant potential in V-band millimeter-wave (mmW) applications. [ABSTRACT FROM AUTHOR]

This article proposes a low-profile, dual-polarized $4\times 4$ antenna array for the fifth-generation (5G) applications. It originates from our previous linear-polarized design, but with two split dipoles. For each polarization, the current on the split dipoles will cancel each other out in one direction. In contrast, in the orthogonal direction, the current can be regarded as a driven dipole to couple energy to four parasitic patches. The proposed element has a profile of only $0.073\lambda _{0}$ (where $_{\mathrm {}}\lambda _{0}$ is one free-space wavelength at 27.85 GHz) with simulated standing wave ratio (SWR) < 2 from 22.11 to 33.6 GHz (BW ≈ 41.25%). The average gain is 8 dBi, and the peak gain reaches 10 dBi at approximately 31.5 GHz. Besides, the two polarizations possess almost the same performance due to the symmetry of the antenna. A 4 $\times 4$ antenna array is designed, simulated, and experimentally demonstrated based on a subarray that can support two orthogonally mode excitations. The measured results present an overlapped bandwidth of 28.4% and more than 25 dB isolation. In addition, the maximum gains are up to 19 and 18.9 dBi for Ports 1 and 2 excitations, respectively. Our proposed design has great application potential in vehicle-mounted millimeter-wave radar and 5G communications systems. [ABSTRACT FROM AUTHOR]

This article presents a 325–500 GHz single-layer planar Goubau-line antenna with endfire radiation based on substrate mode. The electromagnetic (EM) fields along the Goubau line will penetrate into the substrate due to the substrate modes, which cannot operate well compared with the conventional transmission line. The undesired $E_{\text{z}}^{11}$ substrate mode is engineered here to achieve vertically polarized endfire radiation. Since the higher substrate mode is excited and there is a deviation between the propagation constants of the Goubau line and the $E_{\text{z}}^{11} $ substrate mode, the phase difference between the center and edges of the truncated aperture will deteriorate the antenna radiation at higher frequencies. Inspired by the conventional Goubau-line divider, the branches can compensate the wavefront and increase the antenna gain by 2 dB at higher frequencies. This terahertz (THz) antenna on a 300 $\mu \text{m}$ thick quartz substrate ($0.4~\lambda _{0}$ at 400 GHz) possesses robust mechanical properties and consists of single-layer metal, reducing the fabrication complexity. The proposed THz antenna was fabricated and measured, which can operate in a 325–500 GHz band with endfire radiation and achieve 8.5–11.3 dBi gain. [ABSTRACT FROM AUTHOR]

This article integrates several techniques for large-scale, high power-efficiency, and area-efficiency terahertz (THz) radiators. First, we present a systematic design method to synthesize a high output power harmonic oscillator at a high fundamental to maximum oscillation frequency ($f_{\mathrm {osc}}/f_{\mathrm {max}})$ ratio by making a quantitative tradeoff between fundamental oscillation and harmonic output power. Then, a ring scalable coupled oscillator array topology is proposed for a flexible and compact layout. Patch antennas are preferred for large-scale radiator arrays, but the size is much larger than the commonly used slot antenna. Therefore, a miniature on-chip patch antenna is proposed for front-side radiation, whose compact size also helps make the design scalable in 2-D. A quartz superstrate is superimposed on the chip to improve the radiation efficiency. A 16-element ring-coupled oscillator–radiator array is designed and fabricated in a 0.8-mm2 total area using a 65-nm CMOS process to verify the design methods. Maximum radiated power of −2.8 dBm is measured at 472 GHz. This design achieves an area efficiency of 0.66 mW/mm2, the highest among THz radiator arrays using on-chip patch antennas. It is even higher than most radiator arrays using slot antennas. This design also achieves the state-of-the-art dc-to-THz efficiency and frequency tuning range of 0.12% and 4.2%, respectively. The chip can be easily configured to feed a low-cost Teflon lens. A maximum effective isotropic radiated power (EIRP) of ~30 dBm is measured with a 12-mm diameter lens. The measured directivity is 33.7 dBi. At 472 GHz, the measured phase noise is −71.3 dBc/Hz at the 1-MHz offset. [ABSTRACT FROM AUTHOR]

Slot-based cavity antennas are hailed as promising candidates for millimeter-wave applications. Nevertheless, the linear-polarization (LP) angle of their broadside main beam is limited by the slots etched on the cavity’s top surface. In this work, an innovative technique is developed to significantly improve the selection flexibility of their LP inclination angle. It is attained by an integration of a single-layer, closely spaced C-shaped patch surface. A TE710-mode slot-based cavity antenna is employed as the base configuration, which radiates a broadside beam with its LP along $\phi = 90^{\circ }$. To effectively predict and monitor the polarization conversion of the surface-integrated TE710-mode cavity antenna, an analysis method using a unit cavity extracted from its original cavity antenna is presented. A subsequent surface-integrated system with the specified 45° LP was then simulated, fabricated, and measured. The measured results validate that a 45° LP state is achieved with an operating bandwidth from 33.3 to 36.5 GHz. Further investigation is conducted to flexibly choose the LP direction from $\phi = 15^{\circ }$ to 165°. Two more examples with the fabricated antenna prototypes successfully radiate the specified $\phi = 15^{\circ }$ and 75° LP beams, respectively. This near-field polarization conversion surface can be generalized to cavities with different resonant modes. [ABSTRACT FROM AUTHOR]

This work introduces a new design of a Fabry–Perot cavity (FPC) antenna with great filtering response based on a novel filtering feeding scheme. Unlike the traditional method of adopting frequency selective surfaces to achieve filtering characteristic, the proposed strategy focuses on the feeding source. We can obtain an excellent filtering response by utilizing a performance-improved filtering antenna to act as the source of the FPC antenna. To validate the concept, we first propose a new substrate-integrated-waveguide-fed (SIW-fed) filtering antenna element working in a 60-GHz band. By using the slotted radiating patches, two radiation nulls are first generated, respectively, on each side of the operating band. We then design a stepped-impedance waveguide feeding structure and a pair of U-shaped hairpin lines to introduce another two radiation nulls to improve the suppression level in the stopband. The proposed filtering antenna prototype shows a −10-dB impedance bandwidth of 57.5–66.6 GHz as well as a maximum gain of 7.9 dBi. Based on such feeding sources, an FPC antenna is developed and validated. It achieves a 3-dB gain bandwidth from 58 to 65.6 GHz, a peak gain of 15.8 dBi, and a suppression level of over 24 dB. The proposed antennas are good candidates in 60-GHz sensing or communications systems. [ABSTRACT FROM AUTHOR]

The incoming 5G and beyond 5G wireless communications provide unprecedented ultra-high-speed transmission data rates. This is enabled by driving the carrier frequency up to millimeter-wave (mmWave) and terahertz (THz) bands and developing advanced multiplexing technology to increase spectrum bandwidth and spectral efficiency. In this article, we present novel discrete lens antenna designs to solve the two leading open challenges of orbital angular momentum (OAM) applications in mmWave and THz bands: OAM multiplexing and the diffractive problem of OAM waves. For discrete lens antennas operating at THz frequencies, the emerging 3D printing technology and its superior geometric flexibility are utilized to design and implement OAM antennas. The successful demonstration of the mmWave and THz OAM discrete lens antennas can open avenues for future several-hundred-gigabits-per-second wireless communications. [ABSTRACT FROM AUTHOR]

In this article, a wideband filtering antenna based on substrate integrated waveguide (SIW) structure for millimeter-wave (mm-wave) applications is proposed and studied. The proposed antenna is developed using multilayer printed circuit board (PCB) technology. It consists of an SIW feeding structure with a coupling slot, differential-fed $L$ -shaped probes as well as radiating patches. Such architecture provides wide impedance bandwidth along with good filtering characteristic in the lower stopband. Simultaneously, by introducing a pair of open slots on the individual radiating patch as well as two shorting loops on top of the coupling slot, good filtering response in the upper stopband is obtained. The suppression level in the lower stopband is then further improved by introducing a pair of shorted stubs in the coupling slot region. The proposed filtering antenna features no extra filtering circuits, but has wide bandwidth as well as low profile. To verify the proposed structure and design philosophy, antenna array prototypes have been designed, fabricated, and measured. It achieves a 29% bandwidth from 23.5 to 31.5 GHz. Good agreement is achieved between simulated and experimental results. The proposed antenna array is particularly suitable to be applied in 5G (the fifth generation) mm-wave backhaul communications. [ABSTRACT FROM AUTHOR]

A wide impedance-bandwidth and gain-bandwidth terahertz (THz) on-chip antenna (OCA) with chip-integrated dielectric resonator (CIDR) backed by a ground plane is proposed in this article. The antenna uses the inherent silicon substrate in complementary metal–oxide–semiconductor (CMOS) technologies as a rectangular dielectric resonator (DR), that is, the CIDR. This CIDR can be seen as a standard dielectric resonator antenna (DRA) or a magnetic wall cavity with in-phase reflected waves from the ground. A versatile comb-shaped dipole antenna is designed above the silicon CIDR, functioning both as a feeder for the DRA and an independent radiator. With the proper design of the CIDR and the dipole, multiple higher order DR modes and the cavity mode are simultaneously excited, namely, hybrid DR–cavity modes. The hybrid modes greatly expand the bandwidth and improve the gain. Simulations show that the −10 dB impedance bandwidth and 3 dB gain bandwidth are 50% and 34.5%, respectively, while a peak gain of 6.5 dBi is achieved at 305 GHz. For validation, the antenna is fabricated using the Taiwan Semiconductor Manufacturing (TSMC) 65 nm CMOS technology and tested by dedicated THz measurement setups. The fabricated sample shows a peak gain of 8.6 dBi and a maximum radiation efficiency of 44% at 295 GHz. Meanwhile, low cross-polarization levels and stable patterns are also observed. The features of wide bandwidth, high gain, and low profile make the antenna a good candidate in fully integrated THz transceiver systems. To the best of the authors’ knowledge, this is the widest fully integrated OCA working at THz frequencies. [ABSTRACT FROM AUTHOR]

In this article, a holograph-inspired flat lens antenna capable of simultaneously transmitting two independent coaxially propagating orbital angular momentum (OAM) beams operating at 60 GHz is proposed. In the flat lens design, holographic theory including the processes of recording and reconstruction are developed to obtain the desired compensation phase distribution of the flat lens. Novel wideband C-shaped polarization-conversation transmit array element and broadband magneto-electric (ME) dipole antenna are designed as the building block and feed source of the flat lens, respectively, resulting in the wideband performance of the whole antenna. The ME dipole sources do not carry OAM modes while the flat lens can transform the spherical wavefront from the two ME dipole sources into transmitted vortex waves with different OAM numbers ℓ = −1 and +1 simultaneously. For validation, an antenna prototype was fabricated and the radiation performances including return loss, isolation between the two OAM channels, near-field, and far-field performance are experimentally characterized. Both numerical and experimental results validate that the designed flat lens antenna can successfully demonstrate OAM mode multiplexing. The proposed OAM-multiplexing antenna shows promising potential in millimeter-wave high-speed wireless communications. [ABSTRACT FROM AUTHOR]

High-gain millimeter-wave antennas based on spoof surface plasmon polaritons (SPPs) are proposed in this article. Since the dispersion of spoof SPP modes supported by metallic grooves is insensitive to their lateral width, we propose two millimeter-wave antennas with wide SPP grooves, namely an SPP tapering rod antenna and an SPP leaky-wave antenna. The widened grooves enlarge the aperture size of the antennas, enhancing the antenna gains. Both antennas are fed by a standard waveguide and are fabricated by 3-D printing with surface metallization. Based on the similar principle of conventional dielectric rod antennas, the proposed SPP rod antenna achieves broadband and high gain. The measured |S11| is below −16.5 dB from 50 to 75 GHz, and the antenna gain varies from 16.06 to 19.3 dBi. By employing periodic modulation, the SPP leaky-wave antenna operates from 50 to 70 GHz for |S11| below −10 dB. This leaky-wave antenna with 24 modulated periods achieves 20.1–23.9 dBi gain in the operating band with a beam-scanning range from −39° to −3°. [ABSTRACT FROM AUTHOR]

An endfire circularly polarized (CP) complementary antenna array is proposed for 5G applications. The proposed antenna is realized using a single-layered printed circuit board (PCB) with plated-through-hole technology and metal blocks. The antenna element consists of an open-ended substrate-integrated waveguide (SIW), an electric dipole, a double-sided parallel-strip line (DSPSL), and two metal blocks. It is simple in configuration and can achieve wide impedance and axial ratio (AR) bandwidths, stable gain and radiation patterns, and low back radiation. To increase the gain, a $1 \times 8$ antenna array is formed by integrating eight antenna elements with a planar 1–8 SIW feed network. The measurement results show that the proposed array can achieve an overlapping impedance and AR bandwidth of 23.8% from 56.3 to 71.5 GHz with an endfire left-handed CP (LHCP) gain from 14 to 15.3 dBic. The proposed array possesses all the salient features of the complementary source in symmetric and stable radiation patterns, low back radiation, and wide bandwidth. [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) differentially fed magnetoelectric dipole (ME-dipole) array is proposed for fifth-generation applications. The proposed transmission-line-excited antenna, fabricated on a printed circuit board, can achieve wide impedance and axial ratio (AR) bandwidths and high gain. The antenna consists of a $2 \times 2$ ME-dipole array enclosed by a circular cavity. It is modified from our previous work on linearly polarized (LP) array with its element orientation selectively rotated by ±45° with respect to the differentially fed transmission line and the use of sequential rotation technique to generate CP radiation. A differential feed network is utilized to feed the prototype for experiments. Experiments show that the antenna can present an overlapping impedance and AR bandwidth of 32.2% from 52.2 to 72.2 GHz with a broadside left-handed CP gain from 10.2 to 11.8 dBic. The proposed CP antenna retains all the salient features of our previously proposed LP antenna in symmetric and stable radiation patterns and relatively low back radiation levels. [ABSTRACT FROM AUTHOR]

In this paper, we report the design and realization of 2-D focus scanning of the reflected beam by exploiting the frequency dispersion characteristic of reflectarrays operating at terahertz (THz) frequencies. In the first design, we choose four focal points on a circular path at four different frequencies ranging from 0.225 to 0.3 THz and 2-D beam scanning in the focal plane is achieved as frequency increases. To increase the scanning area, we design a dual-band reflectarray and 1-D scanning is achieved in each of the operating bands with different focal positions along the direction orthogonal to the scanning. The proposed reflectarrays are fabricated and their 2-D focus-scanning abilities are measured and there are good agreements between the simulation results and the measurements. The proposed designs demonstrate and expand further the potential applications of reflectarrays in fast THz imaging and detection. [ABSTRACT FROM AUTHOR]

A differentially driven transmission-line-excited magnetoelectric dipole (ME-dipole) is designed for fifth generation applications. The proposed antenna, realized using a single-layered printed circuit board with the plated-through-hole technology, is simple in configuration yet can achieve wide bandwidth and high gain. The antenna is composed of a $2 \times 2$ ME-dipole array surrounded by a rectangular cavity. A differential feed waveguide network based on an E-plane tee is also introduced to feed the prototype for measurements. Measurements show that the proposed antenna with the differential feed network can present an impedance bandwidth of 29.2% from 52.6 to 70.6 GHz with a broadside gain from 10.9 to 13.7 dBi. The proposed antenna retains all the salient features of ME-dipole in symmetric radiation patterns and relatively low cross-polarization and back radiation levels. The radiation patterns are mostly stable with the sidelobes that increase toward the higher end of the operating band. [ABSTRACT FROM AUTHOR]

A millimeter-wave sinusoidally modulated (SM) leaky-wave antenna (LWA) based on inset dielectric waveguide (IDW) is presented in this paper. The proposed antenna, radiating at 10° from broadside at 60 GHz, consists of a SM IDW, a rectangular waveguide for excitation and a transition for impedance matching. Fundamental \textTE01 mode is excited by the IDW with the leaky wave generated by the SM inset groove depth. The electric field is normal to the metallic waveguide wall and thus reduces the conductor loss. As a proof of concept, the modulated dielectric inset as well as the dielectric transition are conveniently fabricated by 3-D printing (\tan \delta=\text0.02). Measurements of the antenna prototype show that the main beam can be scanned from -\text9^\circ to 40° in a frequency range from 50 to 85 GHz within a gain variation between 9.1 and 14.2 dBi. Meanwhile, the reflection coefficient \vert\textS11\vert is kept below -\text13.4\ \textdB over the whole frequency band. The measured results agree reasonably well with simulations. Furthermore, the gain of the proposed antenna can be enhanced by extending its length and using low-loss dielectric materials such as Teflon (\tan \delta < \text0.002). [ABSTRACT FROM PUBLISHER]

A new size-reduction technique for circularly polarized (CP) patch antenna with the use of parasitic shorting strips is presented. The operating frequency of the CP patch antenna can be controlled by those parasitic shorting strips. Rectangular, U-shaped, and meandering shorting strips are studied. It is found that the size and the back radiation of the patch antenna can be reduced simultaneously. Good impedance matching and CP radiation characteristics can be achieved with different shapes of the shorting strips. The proposed antenna with meandering shorting strip is measured. Good agreement between analytical and experimental results is obtained. [ABSTRACT FROM PUBLISHER]

This paper presents a low-cost circularly polarized (CP) small antenna for handheld satellite communications terminals in S-band. It consists of an elliptical vertical patch antenna (VPA) element backed by an elliptical air cavity of different ellipticity. Two dielectric substrates, each with an elliptical opening, are stacked together and mounted onto a ground plane. The rim on the smaller opening of the upper substrate is conveniently plated with conductor to form the VPA, whereas the larger opening of the lower substrate and the ground plane forms the air cavity. The elliptical VPA, when excited by a probe feed, generates CP radiation. Dielectric loading of the VPA not only achieves its size reduction but also widens the 3-dB beamwidth. The fabricated antenna has a measured gain of 5.1 dBic at 3.71 GHz, impedance bandwidth of 12.6%, 3-dB beamwidth of 102° and axial-ratio beamwidth (\bf AR < \bf 3.0\;\bfdB) of 121°. [ABSTRACT FROM PUBLISHER]

This paper presents a novel differentially-fed wideband patch antenna working at millimeter-wave band. The antenna is fabricated using conventional low-cost printed-circuit-board and plated-through-hole technologies and the patch size of the element has been enlarged by exploiting higher-order mode operation for good fabrication tolerance. The antenna element is a 0.86 guided wavelength (\lambdag at 60 GHz) long patch shorted at one end. A slot of 0.09 \lambdag in width is introduced on the shorted patch and the distance between the slot center to the other end of the patch is 0.5 \lambdag. The shorted patch resonates at TM30 mode and the 0.46\lambdag patch, created by presence of the slot, operates at TM10 mode. The combination of these two modes broadens the impedance bandwidth of the element to 18%. Asymmetric radiation patterns in the E-plane and large cross-polarization levels in the H-plane generated by a single patch are eradicated by feeding two mirrored elements differentially. The designed differentially-fed prototype has more than 18% measured impedance bandwidth, stable gain at 9–10 dBi and symmetric and stable radiation patterns across the operating band from 56 to 67 GHz. [ABSTRACT FROM PUBLISHER]

A special sampling path is proposed to improve the accuracy of the discrete complex image method (DCIM) in evaluating the lateral wave. Different from all the previous DCIM implementations, the proposed sampling path goes through the branch point directly, which helps to evaluate its contribution to the lateral wave more accurately. In this communication, different sampling paths of DCIM have been implemented and compared. It is found that in the situations where the lateral wave dominates the far-field region, DCIM with the new path gives more accurate and stable results. [ABSTRACT FROM PUBLISHER]

In the above article , Wu et al.. would like to point out a figure misuse caused by our negligence when editing. Fig. 21 in the original article is updated as Fig. 1 in this correction. [ABSTRACT FROM AUTHOR]

The objective of this paper is to provide the context, physical insight, and perspective on antennas in wireless communications. Although it does not mean to be comprehensive, the four key technologies related to small antenna designs to be reviewed and discussed, including multiband planar inverted-F antennas, broadband folded patch antennas, compact differentially fed antennas, and miniature circularly polarized patch antennas, would cover a wide range of topical interests and practical applications. A brief overview of computer software for analyzing these antennas is also provided. Hopefully, this paper will be beneficial for the diverse engineering readership of the IEEE. [ABSTRACT FROM PUBLISHER]

This paper presents a novel method for size reduction of patch antennas by introducing an irregular ground structure to provide capacitive and inductive loading to the patch. Each of the four corners of the square patch is assigned with a pair of metallic walls. These special metallic walls located underneath the patch are constructed and integrated within the microwave substrate by connected vias. The vertical portion of the walls introduces the inductance whereas the separation between the two parallel walls creates the capacitance. Additional capacitances are also created between the flat strips connecting the vias and the radiating patch. No modifications are made to the square patch. With the presence of the substrate integrated irregular ground (SIIG) structure, the antenna finds a significant size reduction by the capacitive and inductive loading effect. For the proposed linearly-polarized antenna operating at 2.635 GHz, we achieve a total patch area reduction of 75.6% experimentally when compared with a half-wavelength patch antenna loaded with the same substrate. Furthermore, by using two sets of connecting strips with different lengths, two orthogonal modes are excited for circular polarization and similar size reduction effect is achieved. [ABSTRACT FROM PUBLISHER]

A printed microstrip window antenna is proposed in this paper. The window antenna is obtained by perforating a conventional microstrip patch antenna into a window-like geometry. This perforation not only induces a size reduction of more than 50%, but also makes it possible for antenna and RF circuits to be integrated into a unified subsystem by embedding passive and active circuits into the windows of the antenna. The 10 dB return-loss bandwidth of the window antenna is 1.7%, with a gain of 3.7 dBi. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 192–194, 2002. [ABSTRACT FROM AUTHOR]