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In this paper, the design of an ultrathin highly transmissive angular graded-index metasurface (AGIMS) lens is proposed, and a beam steerable high-gain low-profile lens antenna is designed using AGIMS lens and microstrip patch antenna (MPA) radiator operating at 10.10 GHz. An ultrathin graded-index metasurface lens is designed using fundamental unit cells and their modulated forms. The direction and gain control of the microwave radiator's beam, using a designed modulated metasurface lens with doubled-sided double circular ring resonator as a fundamental unit cell, is presented. The uniform radial and linear movement of AGIMS in the step of 12 mm steer the radiated main beam of MPA continuously in a conical plane from −40° to +40° with a maximum measured broadside gain of 13.15 dBi and minimum broadside gain of 11.80 dBi at 10.10 GHz frequency, indicating maximum and minimum gain enhancement of 8.40 and 7.0 dB in −40° and 0° direction, respectively. The angular movement of AGIMS over the MPA radiator at the centre point results in beam steering from −25° to +25° continuously with a maximum gain variation of 2 dB and a maximum measured gain from 10.00 dBi to 12.00 dBi, indicating gain enhancement of 5.25 dB to 7.25 dB. Using AGIMS, the stable broadside radiation characteristic with beam steering and continuous gain enhancement is achieved. The measured and simulated results are in good agreement. [ABSTRACT FROM AUTHOR]

Two types of cost-efficient antennas based on dielectric gradient index dielectric lens have been designed for 5G applications at 28   G H z . The first is a linearly polarized flat lens antenna (LP-FLA) for terrestrial 5G communications. The second is a novel circularly polarized stepped lens antenna (CP-SLA) for 5G satellite services. An efficient design method is presented to optimize and conform the lens topology to the radiation pattern coming from the antenna feeder. The LP-FLA is fed by a traditional linearly polarized pyramidal horn antenna (PHA). The CP-SLA is fed by an open-ended bow-tie waveguide cavity (BCA) antenna. This cavity feeder (BCA), using cross-sections with bow-tie shapes, allows having circular polarization at the desired frequency bandwidth. The two types of presented antennas have been manufactured in order to verify their performance by an easy, low-cost, three-dimensional (3D) printing technique based on stereolithography. The peak realized gain value for the flat (LP-FLA) and stepped (CP-SLA) lens antennas have been increased at 28   G H z to 25.2 and 24.8   d B i , respectively, by disposing the lens structures at the appropriated distance from the feeders. Likewise, using an array of horns (PHA) or open-ended bow-tie waveguide cavity (BCA) antenna feeders, it is possible to obtain a maximum steering angle range of 20° and 35°, for a directivity over 15   d B i and 10   d B i , in the planar and stepped lens antennas, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a new type of flat gradient index lens used for the beam shaping of a miniaturized magnetoelectric transverse electromagnetic (ME‐TEM) horn antenna. Novel metamaterial unit cells with variable sizes are proposed to achieve high refractive index distribution. After applying the novel meta‐lens to the modified transverse electromagnetic horn, the inherent E‐plane beam squint of the low‐profile ME‐TEM horn is corrected. The radiation patterns in E‐plane and H‐plane are focused and the peak gain at 4 GHz is improved to 17.3 dBi. The −10 $-10$ dB matching bandwidth of 0.4–4 GHz is achieved while the measured S11 ${S}_{11}$ is a little poor at 0.8 GHz. The length of the total antenna is still shorter than half of the largest wavelength. The application potential of the gradient index meta‐lens in the low‐frequency band is verified. [ABSTRACT FROM AUTHOR]

A Phase- and amplitude-adjustable metasurface radome (PAMR) is proposed to achieve a wideband high gain and low radar cross-section (RCS) antenna with arbitrary sidelobe levels (AS-PGMA) at a 9.8 GHz operating frequency. The proposed PAMR is a special multilayer phase gradient metasurface lens whose amplitude distribution is modified based on the Dolph-Tschebyscheff technique. The AS-PGMA simulation results indicate that a high gain, low RCS, and low sidelobe level (SLL) antenna can be achieved over a broad impedance frequency bandwidth of 9.25–10.1 GHz with in-band average values of 17 dB, −7.5dBsm, −20 dB/−27 dB for gain, RCS, and E-/H-plane SLL, which are measured at 9.8 GHz as 17.4 dB, −9dBsm, and −23.02 dB/−27.91 dB, respectively. Additionally, a novel analytical method for calculating the RCS of the proposed PAMR and AS-PGMA is described and verified by measurement and simulation findings. Measurement results show that the E-/H-plane SLL of the AS-PGMA is improved by 12.2 dB/5.1 dB at the operating frequency, respectively, while its gain and RCS reduction are reduced by 1.6 and 2.1 dB, respectively. Moreover, RCS of the AS-PGMA is reduced over an ultrawide bandwidth of 1–20 GHz for orthogonal polarizations. The analysis, simulations, and measurements are all in good agreement. [ABSTRACT FROM AUTHOR]

This paper proposes a millimeter-wave lens antenna using 3-dimensional (3D) printing technology to reduce weight and provide stable gain performance. The antenna consists of a four-layer cylindrical gradient-index (GRIN) lens fed by a wideband Yagi antenna. We designed a fractal cell geometry to achieve the desired effective permittivity for a GRIN lens. Among different candidates, the honeycomb structure is chosen to provide high mechanical strength with light weight, low dielectric loss, and lens dispersion for a lens antenna. Therefore, the measured peak gain was relatively flat at 16.86 ± 0.5 dBi within 25−31.5 GHz, corresponding to 1 dB gain bandwidth = 23%. The proposed 3D-printed GRIN lens is cost-effective, with rapid and easy manufacturing. [ABSTRACT FROM AUTHOR]

A high‐gain antenna with multi‐layer phase‐gradient metasurface (PGMS) lens is proposed. It consists of three parts, feed antenna, PGMS lens and back cavity. The proposed PGMS can transform quasi‐spherical electromagnetic wave to plane wave within the frequency band 5.5–6.5 GHz. The half‐power beamwidth of the feed antenna is reduced by up to 83.1°, and the gain is increased by up to 8.7 dB. Because the loading of the lens increases the back lobe, this article also introduces an antenna back cavity, which reflects the energy radiated from the antenna back to the front, thereby improving the radiation performance of the feed antenna. The measured results are in good agreement with the simulation results, verifying that the loading of the lens and the back cavity can achieve the purpose of increasing the gain and reducing the back lobe. The cavity‐backed lens antenna provides potential application for microwave imaging and wireless communication. [ABSTRACT FROM AUTHOR]

In this article, a dual‐band double circularly polarized wide‐angle beam scanning transmitarrays antenna is presented. The transmitarrays antenna can convert the spherical wave into plane circular polarized wave at 20 and 30 GHz bands at the same time and same direction with wide‐angle beam scanning characteristic. The unit cell consists of two kinds of Jerusalem Cross to achieve phase shift ranging from 0° to 300° at 20 GHz, from 0° to 312° at 30 GHz with acceptable loss. The fabricated antenna has a wave beam‐scanning angle from 1.5° to 52.5° at 20 GHz and from 1.3° to 51.6° at 30 GHz. The maximum gains are 22.1 dBic at 20 GHz and 25.0 dBic at 30 GHz. [ABSTRACT FROM AUTHOR]

In this article, a new transmitarray (TA) antenna is designed and fabricated based on Huygens metasurfaces (HMSs). An analytical method has been used to achieve the distribution of surface parameters equivalent to HMS. In this method, the required equations for computing the surface parameters are derived using ray tracing, generalized sheet transition conditions, and two conditions of local power consumption and local impedance equalization. In order to implement these surface parameters, wire and loop unit cells are utilized, which are exposed to the radiation transversely. The array of these unit cells offers high aperture efficiency broadband TA antennas in low aperture profile. The fabricated TA antenna with a low aperture thickness of $0.2\lambda $ exhibits the bandwidth, sidelobe level (SLL), and cross-polarization level of 14%, −19 dB, and −19 dB, respectively. In addition, the high aperture efficiency of 65% is reached with this TA, which shows great improvement in comparison to previous works. [ABSTRACT FROM AUTHOR]

The Luneburg lens is an effective way to implement multibeam antennas. However, the existing planar Luneburg lens configuration usually can only provide a relatively narrow scanning range. To deal with this problem, a Luneburg lens consisting of one dielectric cylinder and nine dielectric rings is proposed. It can be easily fabricated using low cost ABS material through 3D printing technology. The lens is placed between two metal plates which have an additional flare structure to enhance the antenna gain. To effectively excite the lens for multibeam applications, 9 magneto electric dipoles are utilized. For validation, a wide‐angle scanning planar Luneburg lens antenna operating at 35 GHz was designed, fabricated and measured. A good agreement between simulation and measurement can be observed. At the center frequency, a wide scanning coverage of 172° can be obtained with a gain variation less than 1.6 dB. [ABSTRACT FROM AUTHOR]

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 long focal length, suffer from limited volume reduction, severe reflection, narrow beamscanning range (BSR), and low capture efficiency. The proposed TO mapping in this article, engendered by transforming the upper and lower parts of the original LL separately, preserves the original beamsteering property of an LL in half a space with the focus retained at its flat surface before exerting any index approximations. The effects of the approximations and the discretization on the performance of the transformed LL are then investigated and analyzed comprehensively. After that, a hemispherical lens with a radius of 60 mm is exemplified at X-band and fabricated using a ten-layered nonresonant gradient index MTM. The designed TO-based LL is fed by a stacked patch antenna linearly shifted at a distance of 4 mm (a focal-to-diameter ratio of 0.03) beneath the lens to achieve a wide beamsteering range of ±41° with a maximum gain of 15.7 dBi and a gain tolerance of 1.7 dB. The proposed TO-based metalens antenna features compactness with a near-surface focal plane, wide BSR, and easy fabrication, which shows potential applications in far-field imaging, radar, and 5G wireless communication. [ABSTRACT FROM AUTHOR]

The millimeter-wave band is a very attractive frequency band for the new generations of mobile cellular networks, i.e. 5G and 6G, due to its potential to support extremely high data rate transmissions. Innovative antenna solutions are needed to relieve the higher free space attenuation at these frequencies. Here, we propose a multibeam antenna based on a geodesic lens with stable aggregate gain characteristics in the far-field. An analytical model based on the physical path of the rays inside the lens is applied to achieve the field distribution in the aperture of the lens. This method is used to find the profile of a near-field focusing lens with a widened beam in the far-field. As a proof of concept, a seven-beam antenna has been designed. Due to the rotational symmetry of the geodesic lens, the antenna beams present similar characteristics over an extended sectorial coverage. The lens antenna has been manufactured, and its near-field focusing features were validated. The prototype has been assessed also in the far-field with a good agreement between model, simulations, and measurements. The main novelty of this prototype is to achieve a multiple beam coverage within $\pm 67^\circ $ in the H-plane and $\pm 20^\circ $ in the E-plane, with a gain roll-off smaller than 2 dB at 30 GHz and smaller than 3 dB at 35 GHz. These results validate the stable aggregate gain characteristics in the far-field of the proposed solution. [ABSTRACT FROM AUTHOR]

This research applies Effective Medium Theory and 3D Finite Element Analysis to model the transmissive loss through a waveguide fed additively manufactured Luneburg lens. New results are presented that provide rational function approximations for accurately modeling the aperture, beam, and radiation loss factors of the antenna. It introduces a normalized loss tangent and shows that the loss factors are dependent on the product of this parameter and the lens radius. Applying the constraint that the main beam of the radiation pattern contains 50% of accepted power, a maximum useful radius is tabulated for common polymers used in additive manufacturing. [ABSTRACT FROM AUTHOR]

For a base station antenna in 5G mobile communications, lens antennas have been proposed for excellent multiple beam performances. In this paper, the negative refractive index (NRI) lens is selected for thinning the lens thickness. By applying lens shaping method, straight-line condition lens is designed. Multi beam radiation characteristics are compared with the conventional hyperbolic shape lens and Abbe's sine condition lens. In order to determine the feed positions for multi beam performances, the focal region ray tracing is performed. The best feed positions are obtained. For calculating multi beam radiation characteristics, ANSYS HFSS software is employed. Multi beam radiation patterns in the wide angle scanning up to 45° are obtained. The results show that the proposed straight-line condition lens achieves higher gain and lower sidelobe level compared to the other two structures. The usefulness of the proposed lens antenna is ensured. [ABSTRACT FROM AUTHOR]

In this article, a new method to design an ultrawideband beam-steering antenna system is presented. The system is completely passive and suitable for millimeter-wave applications, including some in defense, where both discrete beam steering and continuous beam steering in two dimensions (elevation and azimuth) are required at a reasonably fast speed. The beam-steering capability is achieved using a pair of distinct low-profile and planar phase transformers (PPTs) placed in the near-field region of a fixed-beam radiating source. The antenna system demonstrates a steering and impedance-matching bandwidth of 28.6%, from 30 to 40 GHz. A prototype of the new antenna system, including a pair of thin PPTs and a completely automated mechanical system to rotate each of the PPTs around the antenna axis, has been fabricated and tested. The pair of rotating PPTs, equivalent to a pair of 3-D dielectric PTs (DPTs), introduces a precalculated phase gradient to the input near field from the fixed-beam antenna and creates an output near field that will radiate toward a selected direction, which can be varied within a large conical region with a maximum apex angle of 108°. The system exhibits the predicted and measured peak gains of 21.5 and 21.7 dBi, respectively, and the measured gain variation over 2-D beam steering is less than 2.2 dB. This beam-steering method obviates the need for expensive phase shifters and distribution networks, which are also lossy at mm-wave frequencies. The measured results validate the predicted wideband matching and steering performance of the system with a close agreement. [ABSTRACT FROM AUTHOR]

A continuous beam-steering solution for circularly polarized (CP) radial-line slot array (RLSA) antennas is presented and demonstrated with a fabricated prototype. The solution is based on the near-field meta-steering (NFMS) method, which is implemented through a pair of highly transmitting hybrid metasurfaces (HMs) that are placed above a high-gain CP RLSA antenna in the near-field region. Cells in HMs, unlike conventional metasurfaces (CMs), can provide exact or close to exact phase shift with transmission magnitude larger than −1 dB. This is achieved by combining the nonoverlapping phase ranges of two dramatically different phase-shifting cells. The RLSA is stationary, while the two HMs are rotated to steer the beam in a 2-D (azimuth and elevation) space. The measured results of the prototype demonstrate that the system can steer its beam to a maximum elevation angle of 40.6° with a maximum gain of 30.9 dBic. The axial ratio remained less than 3 dB in the 3 dB beamwidth even when the beam is steered. The height of the system is only 4.5 cm, which is much less than mechanically steered reflector antennas. Unlike electronically steered high-gain antenna arrays, this system requires only few watts of power only when rotating HMs and has zero power consumption when the beam is stationary. [ABSTRACT FROM AUTHOR]

This communication presents a very thin metasurface (MS) planar lens for millimeter-wave (mm-wave) MIMO applications. The MS planar lens consists of array of mm-wave resonators providing varying phase response to transform the phase profile of the electromagnetic wave propagating through this array. Each resonator consists of two identical layers having substrate separated by an air gap of ${h=0.8}\,\,{\text {mm}}$ and is ${4} \,\,{\text {mm}}{\times } 4\,\,\text {mm}$ in size. The MS lens having a focal length of $f=12\,\,\text {mm}$ is loaded to a three-port proximity fed antenna array to operate at 27.5–32 GHz. The designed lens is polarization-insensitive and can be used with any polarization. The three-port antennas with the MS lens is fabricated and tested, and the measured results have confirmed a beam scanning of ±15° with a peak gain of 20.2 dBi for port-2. [ABSTRACT FROM AUTHOR]

Near-field electromagnetic focusing has become a hot research topic due to its high application value in wireless transmission, wireless sensing, biomedicine, and radio frequency identification. In this paper, anisotropic metasurfaces have been proposed to manipulate the phase of the electromagnetic (EM) wave for obtaining EM near-field focusing. Under orthogonal linearly polarized incidence, dual focus functions can be realized independently for polarization multiplexing on the metasurfaces. Meanwhile, Single focus and multi focus with different energy distributions and focal position is obtained by the proposed metasurfaces. By using the Vivaldi antenna as the feed source positioning at the focal of the metasurfaces, a lens antenna with high gain is obtained with circularly polarized far-field mode and broadband characteristics. Due to the unique advantages of metasurfaces in modulating the phase distribution of EM waves, the proposed method may pave a new way for EM focusing application. • Dual focus functions can be realized independently for polarization multiplexing on the metasurfaces. • Single focus and multi focus with different energy distributions is obtained by the proposed metasurfaces. • A lens antenna made of Vivaldi and focusing metasurfaces is obtained with circularly polarized far-field mode. [ABSTRACT FROM AUTHOR]

In this paper we present a lens antenna for 3D beam steering at microwave frequencies. Over the azimuth, 360° beam steering is realized through exploiting the orbital angular momentum (OAM) property of the electromagnetic wave components of the beam. A beam pointing toward a certain direction in the azimuth is optimized by an appropriate superposition of waves carrying different OAM orders; the beam direction is manipulated by the relative phase shifts between waves. The elevation of the beam is separately controlled by coupling the OAM wave generators to a Maxwell fish-eye lens. The proposed antenna operates with high directivity, narrow beamwidth, and low side lobe levels over a wide spatial steering range. Among the results, a stable beam of about 10.8 dBi main lobe gain, 3 dB beamwidth of 17.4°, and - 4.7 dB sidelobe level is synthesized over wide azimuthal and elevation ranges. The effects of the characteristics of the lens on beam steering are analyzed in detail. The method has been demonstrated to work effectively by numerical simulations. [ABSTRACT FROM AUTHOR]

A high gain oversized annular lens antenna for 28‐GHz band channel measurement system is presented. The proposed antenna is composed of an omnidirectional feeding source and an oversized annular lens. The feeding source is a compact multi‐stepped biconical antenna with a wide impedance bandwidth. By rotating a horizontally placed two‐dimensional extended hemispherical lens around the vertical axis, the oversized annular lens is realized, which effectively increases the vertical radiation aperture and maintains high aperture efficiency to enhance the omnidirectional gain. Under the same envelope, the proposed antenna features a higher gain than the biconical antenna and the ordinary annular lens antenna. A prototype is fabricated and measured. The measured results demonstrate that the ‐10‐dB impedance bandwidth is 20.7% (24‐29.6 GHz), with stable vertically polarized (VP) omnidirectional radiation patterns and gain over 10.3 dBi within the entire band of interest. [ABSTRACT FROM AUTHOR]

A dual-polarized $4\times 4$ scanning phased array antenna with leaky-wave enhanced lenses operating at 28 GHz is presented. Such an antenna can be used for point-to-point fifth-generation (5G) communications that require high gain, wide bandwidth (BW), and limited steering ranges. The proposed array has a periodicity of two wavelengths, and the resulting grating lobes are suppressed by directive and steerable array element patterns. To achieve a low-cost and low-profile solution, the leaky-wave antenna feeds are designed in printed circuit board and the lenses are made of plastic. The lenses are optimized in the near-field region of the feeds, with the goal of maximizing the array element aperture efficiency. The array performance obtained from the proposed approach is validated by full-wave simulations, showing a 27.5 dBi broadside gain at 28 GHz and a steering capability up to ±20° with 2 dB of scan loss. An antenna prototype was fabricated and measured. Measurement results are in excellent agreement with full-wave simulations. The prototype antenna, at broadside, achieves a 20% relative BW and a gain of 26.2 dBi. [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]

A three-layered transmitting focusing gradient meta-surface (FGMS) has been proposed, which can achieve broadband gain enhancement from 8.2 GHz to 10 GHz. The element of broadband transmitting FGMS has high transmitting efficiencies that over 0.7 and achieve [0, 2p] phase range with a flat and linear trend in the operating band. The FGMS can transform the spherical waves into plane waves. Three patch antennas working at 8.2 GHz, 9.1 GHz, and 10 GHz respectively are placed the focus of broadband FGMS as the spherical-wave source to build a broadband planar lens antenna system. It achieves a simulation gain of 15.44 dBi which is 7.51dB higher than that of the bare patch antenna at 10 GHz with satisfying SLLs and beamwidths. However, it enhanced the gain of the bare patch antenna in a wide operating band. Finally, the FGMS and the patch antenna are fabricated and measured. The measured results are in good agreement with the simulations. [ABSTRACT FROM AUTHOR]

Lens is an effective antenna solution, the radiation pattern of the antenna can be enhanced through the dielectric lens, the lens antennas tend to be directive rather than omnidirectional that is. However, in this article, a monopole antenna integrated within a three dimensional printing mushroom shape lens and pasted the copper foil on the part of the surface of lens is proposed for wireless electromagnetic energy harvesting system at 5.8 GHz to the realization of a wide beam antenna. The bandwidth is from 5.33 to 6.07 GHz with the reflection coefficient below −10 dB. The half power beamwidth is 197° in x‐z plane and 175° in y‐z plane, respectively. And the peak gain is 2.47 dBi. Simulation results agree well with measured results. [ABSTRACT FROM AUTHOR]

A low‐profile wide‐scanning lens antenna operating at 5G millimeter‐wave (mm‐wave) frequencies (24‐29 GHz) is presented in this article. Based on the principles of parallel plate waveguide, the proposed lens consists of two almost‐parallel plates which have only one slot or ridge in their inner surfaces. Due to that the lens is filled with air, the prominent high loss of dielectric lens at mm‐wave frequencies can be avoided. The 22 monopole antennas are employed to feed the lens, providing over ±77° beam scanning coverage of −3 dB cross‐over level in the azimuth plane. Measured 3 dB beamwidths are 7°/69° in the azimuth/elevation plane at the middle frequency of 26.5 GHz, respectively. Measured aperture efficiency for the middle beam is 66% at 26.5 GHz, and varies between 40% and 69.4% over the operating frequency band. The results indicate that the proposed lens is an effective solution for the 5G wireless communications due to its wide‐angle scanning, lightweight, low cost, and easy fabrication. [ABSTRACT FROM AUTHOR]

A fan‐beam antenna system based on metasurface lenses is proposed for backhaul antenna applications at 10.4 GHz. The planar metasurface lens is composed of three pairs of subwavelength unit cells with high transmission and opposite phase. These phase shifters are arranged to transform the Gaussian distributed near field from a linear patch antenna array into the sin c‐function distributed aperture field, which in turn brings a sector radiation pattern in the azimuth plane and a pencil beam in the elevation plane. The simulated and measured results demonstrate that the presented lens antenna offers a sharp roll‐off fan beam with the azimuth beamwidth 60°, elevation beamwidth 10°, and the gain 18.2 dB with the flat‐top ripple less than 2.0 dB. [ABSTRACT FROM AUTHOR]

A metasurface (MTS) lens array (MLA) fed by a phased array with less phase shifters (PSs) is proposed for compact low-cost beamsteering applications. By dividing a single-large-aperture lens into N small-aperture lens elements with the focus-to-diameter ratio of a lens antenna unchanged, the overall thickness of the proposed antenna is reduced by N times. The beamsteering is achieved in two steps. First, the main beam direction of MLA antenna is switched over a large angular step by shifting the feeding antennas beneath each lens element. Then, the switched beams are fine steered by a low-cost N-element phased array. Theoretical analysis using array theory is performed to work out a general design method with discussion on the taper and spillover effect of feed-power pattern on the lens array. Based on the proposed method, a three-lens linear MLA fed by a phased array is designed to operate at 10 GHz. The proposed antenna achieves a 3 dB beamwidth coverage range of ±30° with a beam crossing level higher than −3 dB and a gain tolerance of 1.6 dB with a maximum gain of 19.1 dBi. The presented antenna can be used to achieve volumetric beamsteering performance directly. The proposed design features the merits of higher gain, lower cost, simpler feeding network, less PSs, and lower profile compared with conventional full phased arrays and single-aperture lens antennas. [ABSTRACT FROM AUTHOR]

The design and experimental validation of a wide scanning dome antenna with reduced profile is presented. The antenna is based on the combination of a planar phased array with limited scanning capabilities and a dielectric lens which allows to broaden the field of view. The angular variation of the scan loss can be almost arbitrarily designed if no constraint is imposed on the size of the dielectric lens. However, the focus of this article is on the size minimization of the dome as required for applications where the form factor is critical. Therefore, a lower boundary of the height of the dome is derived and imposed as a design constraint. The antenna is analyzed using in-house ray tracing and physical optics software tools. It is shown that, when the array is combined with the dielectric dome, a significant directivity enhancement can be achieved for wide scanning. A demonstrator of the lens is designed, manufactured and combined with an available phased array working in $Ku$ -band. The experimental tests confirm the theoretical predictions, validating the analysis tools, and show a scanning range of 70° in all scanning planes over a 15% bandwidth. The directivity is enhanced by approximately 2 dB at the limits of the scanning range compared to the standalone illuminating array. The active element pattern is rotationally symmetric, thus, the radiation performance is almost independent on the scanning plane. Moreover, the dielectric lens allows to preserve the cross-polarization performance of the illuminating array without adding a significant contribution. [ABSTRACT FROM AUTHOR]

In this contribution, a broadband $G$ -band leaky-wave (LW) fed lens antenna with an integrated dielectric grid polarizer is presented. The proposed wideband polarizer unit cell geometry enables its fabrication at frequencies higher than 100 GHz, presenting high transmission properties and low axial ratio (AR). A quasi-analytic technique based on multilayer spectral Green’s function combined with a numerical Floquet modes’ solver is used to optimize the lens aperture efficiency and AR. The proposed technique is validated via full-wave (FW) simulations. A design is proposed in low dielectric permittivity material, achieving FW simulated aperture efficiency higher than 75% over 44% relative bandwidth, and an AR lower than 3 dB over 35% relative bandwidth. The antenna is able to achieve multiple directive circularly polarized (CP) beams when fed by a focal plane array, preserving the AR bandwidth. A prototype has been fabricated and measured, exhibiting an excellent agreement with quasi-analytic and FW simulations. [ABSTRACT FROM AUTHOR]

A beam-steerable lens antenna based on the concept of Risley prism is presented in this communication. The antenna is made up of a feed antenna and three transmit-array (T-A) lenses, including a stationary lens and two rotatable lenses. Beam steering is achieved by rotating the two rotatable lenses around the antenna axis independently. An antenna prototype has been successfully designed, simulated, fabricated, and measured in Ku-band. The results show that the beam of the antenna can be steered to any direction within a 91.2° conical region. During beam steering, the measured peak gain of the antenna reaches 38.1 dBi, the maximum aperture efficiency achieves 80.5%, and the gain variation is less than 1.7 dB. Moreover, the simulated results show that the power-handling capacity of this antenna could reach gigawatt level, which indicates application potentials of this antenna in high-power microwave (HPM) field. [ABSTRACT FROM AUTHOR]

With the widespread use of vehicles, finding an empty parking space in a parking lot has become a problem that most drivers encounter daily, particularly in urban environments. In this article, a 3-D printing high-gain dielectric lens $K$ -band antenna is designed for a smart parking radar system that performs dual-mode detection by using a magnetic sensor to improve the accuracy of parking space detection. The proposed antenna uses a wideband high-efficiency electromagnetic structure (WHEMS) as the primary feed antenna. The primary antenna is etched on a substrate and can be easily integrated with a radio frequency (RF) circuit. The WHEMS antenna has a wide bandwidth that is not influenced by instability in the substrate permittivity. Benefiting from low-cost, fast prototyping 3-D printing technology, a conformal flat semiclosed perforation dielectric lens is designed to achieve a high gain; this lens avoids the measurement unreliability caused by large penetration losses in the $K$ -band. The $K$ -band radar operates at 24–24.25 GHz, with a measured gain of 18.4 dBi. Measurements obtained from the developed system reveal that the proposed high-gain, low-cost, lightweight, durable, integrated design approach is well-suited for a $K$ -band radar smart parking system. [ABSTRACT FROM AUTHOR]

A unified Brewster effect condition is proposed as a guideline for the design of the reflectionless lens. Previously, most of the investigations on the Brewster effect are limited for the homogeneous isotropic medium and the condition is sensitive to the polarization states. Here, it is predicted both theoretically and numerically that an arbitrarily polarized electromagnetic wave can perfectly refract through an anisotropic plate. In particular, both TE- and TM-polarized incident waves can have an identical Brewster angle with total transmission at either normal or oblique incidence by adjusting the material anisotropy. As a proof of concept, we employ this unified theory into the design of a 2-D reflectionless lens with a simplified restriction condition. It is demonstrated that perfect wavefront shaping with no fundamental limits on its efficiency is obtained with the proposed topology. To illustrate practically the concept of Brewster lens, a three-layer cascaded lens is fabricated and measured with a thickness of $0.1\lambda $ and an aperture efficiency of 94.3%. A remarkable 10.3 dB gain increasement is obtained compared with its counterparts. [ABSTRACT FROM AUTHOR]

Placing dielectric lens structures into an antenna's aperture has proven to be one of the most reliable methods of enhancing its gain. However, the selected material and the prototyping method usually limit their fabrication process. With the advances in 3D printing technology and their applications, the microwave designs that were either impractical or impossible in the past to manufacture using traditional methods, are now feasible. Herein, a novel prototyping method by using 3D-printer technology for low-cost, broadband, and high gain dielectric lens designs has been presented. Firstly, the elliptical lens design has been modeled in the 3D EM simulation environment. Then fused deposition modeling based 3D-printing method has been used for the fabrication of the dielectric lens. The measured results of the 3D printed antenna show that the lens antenna has a realized gain of 17 to 20.5 dBi over 8-12 GHz. Moreover, the comparison of the prototyped antenna with its counterpart dielectric lens antenna in the literature has indicated that the proposed method is more efficient, more beneficial, and has a lower cost. [ABSTRACT FROM AUTHOR]

This article develops a flat, miniaturized lens based on metamaterial for antenna gain improvement. The overall size of the lens is 1.9λ0 × 1.9λ0 × 0.05λ0. The distance between the metamaterial lens and the antenna is only about 0.4λ0. The prototype lens antenna is fabricated and the measured results are in agreement with the simulated results. It shows that the proposed lens provides significant gain enhancement by 2 to 3.5 dB between 1.3 and 1.45 GHz, which effectively demonstrate a high directivity, miniaturized, and compact metamaterial lens antenna. [ABSTRACT FROM AUTHOR]

In this article, designing of a low‐profile planar linear graded index metasurface (LGIMS) lens is presented. A wide‐beam steerable high‐gain low‐profile antenna is designed by placing LGIMS over microstrip patch antenna radiator at an optimum height. Direction control of the radiation pattern of the microwave radiator by using amplitude and phase modulated metasurface is achieved. The measured peak gain of 13.50 dBi at an operating frequency of 10.08 GHz with progressively beam steering characteristic and progressive enhanced gain within a large conical region of apex angle 64°. The measured maximum gain tolerance of 2.43 dB with significantly reduced side lobe level is obtained by mechanically moving the ultrathin LGIMS lens along the negative parallel radiator axis. The mechanical movement of LGIMS lens over radiator results in to beam steering up to +32°. A maximum measured gain enhancement of 8.75 dB is achieved. The positive parallel radiator axis movement of LGIMS causes gradual broadside gain enhancement with maximum gain enhancement of 1.5 dB. The measured results are in good agreement with the simulated results. [ABSTRACT FROM AUTHOR]

A design of dual-band beam-scanning antenna using rotatable planar transmitarrays (TAs) is proposed in this communication. The antenna is composed of a dual-band lens and a pair of linear phase gradient (PG) TAs. The presented anisotropic lens is polarization independent, operating at two frequency bands. The PG TA is implemented by using double square loop units with different PGs at two frequencies. Two rotatable PG TAs are located above and parallel to the dual-band lens, and beam scanning in the upper hemisphere is achieved by rotating the two PG TAs synchronously around the axis orthogonal to the planes of the PG TAs. The procedure is demonstrated for dual-band beam-scanning implementation operating in linear polarization at $X$ - and $Ku$ -band. The full-wave simulation results demonstrate that the designed antenna enables beam steering in both azimuth and elevation planes at 8 and 14 GHz, with a peak gain of 16.7 and 19.8 dB in the broadside direction, respectively. Moreover, a prototype is fabricated, and the measured results confirm the feasibility of using this method for achieving low-cost lightweight, simple configuration dual-band 3-D coverage beam-scanning antenna. [ABSTRACT FROM AUTHOR]

This article presents a wideband beam-steering antenna system for high-mobility millimeter-wave (mm-wave) systems. It can provide both continuous and discrete beam steering in two dimensions (elevation and azimuth) at a speed that is sufficient for various applications including some in defense. The antenna is completely passive and beam steering is achieved using near-field phase transformation by employing a pair of distinct rotatable stepped-dielectric phase transformers (SPTs) placed in the near-field region of a fixed radiating source. The antenna system has a steering and impedance-matching bandwidth of 40.6% from 26.5 to 40 GHz. A prototype of the beam-steering antenna system including a mechanical system to rotate each of the SPTs around the antenna axis has been fabricated and tested. The rotating SPT pair introduces a predetermined phase gradient to the input near-field and creates an output near-field that will radiate in an arbitrarily selected direction, which can be varied within a large conical region with a maximum apex angle of 104°. The system exhibits predicted and measured peak gains of 21.5 and 21.25 dBi, respectively, and the measured gain variation over 2-D beam steering is less than 3 dB except at 36 and 39 GHz, where it rises to 3.6 and 3.1 dB, respectively. This beam steering method obviates the need for expensive phase shifters and distribution networks, which are also lossy at mm-wave frequencies. The measured results validate the predicted wideband matching and steering performance of the system with close agreement. [ABSTRACT FROM AUTHOR]

A metasurface lens antenna fed by a planar $8\times8$ dual polarized antenna array is proposed and characterized for full-dimensional massive multiple-input multiple-output (MIMO) and multibeam systems at sub-6 GHz bands. The lightweight multilayer metasurface structure consisting of Jerusalem cross elements is used for a planar lens design. The lens antenna with the size of $10\lambda _{0} \times 10\lambda _{0} \times 5\lambda _{0}$ is fed by an $8\times8$ dual-polarized stacked patch array to operate over the range from 5.17 to 6.10 GHz, where $\lambda _{0}$ is the free-space operating wavelength at the center frequency of 5.6 GHz. This article shows the scanning range of ±25° with a maximum gain of 22.4 dBi and the gain variation of 3.3 dB at 5.6 GHz. Beam coverage performance, pattern envelope correlation coefficient, and port isolation properties demonstrate its full-dimension access capability of the antenna. Besides, the multibeam antenna system with high-gain coverage is achieved by beams operating at the same frequencies, while the frequency division multiplexing can be realized for the isolated beams. The proposed metasurface lens antenna, featuring lightweight, compactness, and low cost compared to a 3-D dielectric lens and low-complexity compared to the array scenarios, can be an alternative for fifth-generation (5G) sub-6 GHz frequency bands. [ABSTRACT FROM AUTHOR]

High-directivity antenna systems that provide 2-D beam steering by rotating a pair of phase-gradient metasurfaces (PGMs) in the near field of a fixed-beam antenna, hereafter referred to as near-field meta-steering systems, are efficient, planar, simple, short, require less power to operate, and do not require antenna tilting. However, when steering the beam, such systems generate undesirable dominant grating lobes, which substantially limit their applications. Optimizing a pair of these metasurfaces to minimize the grating lobes using standard methods is nearly impossible due to their large electrical size and thousands of small features leading to high computational costs. This article addresses this challenge as follows. First, it presents a method to efficiently reduce the strength of “offending” grating lobes by optimizing a supercell using Floquet analysis and multi-objective particle swarm optimization. Second, it investigates the effects of the transmission phase gradient of PGMs on radiation-pattern quality. It is shown that the number of dominant unwanted lobes in a 2-D beam-steering antenna system and their levels can be reduced substantially by increasing the transmission phase gradient of the two PGMs. This knowledge is then extended to 2-D beam-steering systems, where we demonstrate how to substantially reduce all grating lobes to a level below −20 dB for all beam directions, without applying any amplitude tapering to the aperture field. When steering the beam of two meta-steering systems with peak directivities of 30.5 and 31.4 dBi, within a conical volume with an apex angle of 96°, the variation in directivity is 2.4 and 3.2 dB, respectively. We also demonstrate that beam-steering systems with steeper gradient PGMs can steer the beam in a wider range of directions, require less mechanical rotation of metasurfaces to obtain a given scan range, and their beam steering is faster. The gap between the two metasurfaces in a near-field meta-steering system can be reduced to one-eighth of a wavelength with no significant effect on pattern quality. [ABSTRACT FROM AUTHOR]

This paper presents a beam steerable low-profile lens antenna with a flat top wide beam and a high gain operating at 10.10 GHz. It consists of a graded index metasurface (GIMS) lens placed on the top of a microstrip patch antenna (MPA) radiator. An ultrathin linear graded index metasurface (LGIMS) and a radial graded index metasurface (RGIMS) lens were designed for the magnitude and phase transformation of the radiated beam from the microwave radiator. First, an LGIMS lens antenna was designed by placing an LGIMS on the top of an MPA radiator at an optimum height. A maximum measured gain of 16.37 dBi indicating a maximum gain enhancement of 11.50 dB with beam steering in a conical plane with a vertex angle of 84° was observed. Next, a flat top beam (FTB) antenna with a stable gain band was designed by placing an RGIMS on top of an LGIMS lens antenna. The measured peak gain of 14.82 dBi with an FTB pattern having a 1 dB gain variation range of about 96° is observed. Furthermore, the movement of the LGIMS and the RGIMS on top of the radiator results in continuous beam scanning with a maximum gain variation of 1 dB in a conical plane with a vertex angle of about 100°. A maximum gain of 14.82 dBi with a maximum gain enhancement of 10.30 dB at 10.15 GHz was obtained due to the linear and angular movement of the LGIMS and the RGIMS in the FTB antenna. The simulated and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

For the first time, a liquid crystal (LC) filled lens antenna is investigated for beam steering in this paper. The LC’s anisotropy is applied inside a semicircular shaped parallel-plate waveguide to achieve a deflection of the propagating electromagnetic wave at the interface of lower and higher permittivities. Using an electrode network, the direction of the sector of higher permittivity can be adjusted and, therefore, so can the beam direction. The main advantage of this antenna concept is that neither phase shifters nor switching networks are needed, resulting in a very simple approach for beam steering. Operating at $V$ -band, from 50 to 75 GHz, the first demonstrator proves the antenna concept by reconfiguring the beam in predefined directions of −30°, 0°, and +30° to simplify the electrode biasing network. Furthermore, it is feasible and being demonstrated to adjust the beamwidth and to generate multiple beams. In the measurements, the antenna exhibits a measured input reflection below −10 dB over the complete frequency range. For the unsteered radiation pattern, the sidelobe level is between −8 and −12 dB, whereas these values degrade to −4.5 to −6 dB for the steered radiation pattern at ±30°. The measured gain is between 13 and 15 dBi. [ABSTRACT FROM AUTHOR]

A millimeter-wave multi-beam antenna operating dual-band with a 1 GHz bandwidth each, around the 28 and 31 GHz frequencies, is presented. The antenna is designed on the principle of transformation of the cylindrical wavefront to planar to enhance the gain. A metal ridge lens is used for the wavefront transformation by a phase extraction and compensation method. The dual-band operation of the antenna aids in transmitting and receiving at two independent frequencies. An advantage to this is the significant reduction of the number of RF chains due to the use of the shared aperture over the lens. The antenna has been validated for casting the beam in three primary target directions of − 60°, 0°, and 60°, however, other beam directions can be suitably designed. The spatial footprint of the antenna is $170\,\,\text {mm} \times 150$ mm and has a gain varying between 14 and 15 dBi at each of the three ports centered around 28 and 31 GHz. The theoretical simulated results are in good agreement with the measurements. The antenna could potentially be used in 5G small cell deployments of a millimeter-wave local multipoint distribution system (LMDS). [ABSTRACT FROM AUTHOR]

Huygens’ metasurfaces have demonstrated their versatility in numerous applications, such as wide-angle refraction and antenna beamforming. These electrically thin structures allow the enhancement of antenna systems with passive designs. Such enhancements include improving the gain and scanning capability of feed antennas. In this paper, the design, simulation results, and measurements of a metasurface lens for gain enhancement of frequency-scanning slotted-waveguide antennas are shown. Both transverse-electric (TE) and transverse-magnetic (TM) metasurface designs are verified with full-wave simulations, which demonstrate upward of 13 dB of directivity enhancement. Additionally, a fabricated $40\lambda $ long by $15\lambda $ wide TM metasurface lens centered at 34.3 GHz was experimentally verified in conjunction with a TM frequency-scanning slotted-waveguide antenna. The waveguide antenna radiates through a 1-D slot array operating between 33.5 and 35.3 GHz and produces a 16 dB fan beam which scans in the H-plane between −26° and broadside within its operational bandwidth. The realized metasurface lens, placed at $3.05\lambda $ at 34.3 GHz away from the waveguide antenna, was able to increase its realized gain by upward of 10 dB while maintaining its scanning capabilities. With the design verified in both simulation and measurements, the proposed metasurface serves as an easy-to-fabricate, efficient, low-profile, and lightweight alternative to standard microwave lenses. [ABSTRACT FROM AUTHOR]

In this paper, a novel broadband high-gain, circularly polarized planar lens antenna is presented. We used the rotation elements to design a transmission-type polarization conversion planar phase-gradient metasurface (PPGM). By adjusting the rotational angles of the metal patch on the element, we obtained the desired transmission phase shift for PPGM. We used a patch antenna as a feed source, which formed a lens antenna system integrated with the PPGM. The simulation results showed that the PPGM can achieve a high-efficiency, cross-polarization conversion for vertical incidence of a right-handed circularly polarized plane wave. Our numerical and experimental results agreed well with each other, indicating that the antenna system had a peak gain of 18.8 dB, a good axial ratio better than 2 dB at 13 GHz, with an aperture efficiency of 50.56% and a focal length/diameter (F/D) ratio of 0.307. In addition, its -10 dB impedance and 3dB axial ratio bandwidth reached up to 940 MHz. The lens antenna performed well and can be applied in many communication systems. [ABSTRACT FROM AUTHOR]

A planar wavefront transformation lens based on gradient-index metamaterials is proposed. The designed lens is composed of isotropic and inhomogeneous metamaterials and can reach impedance matching with free space. Based on the impedance-matching metamaterial lens, we present a compact high-gain and high-aperture-efficiency horn-based lens antenna working from 8 to 12 GHz. At the center working frequency of 10 GHz, the performance of the antenna is significantly improved and the measured gain increases to 17.7 dBi, which is 6.5 dBi higher than that of the original H-plane horn antenna. The half-power beamwidth and sidelobe level in the H-plane reduces to 6.2° and 15.3 dB, respectively, and the aperture efficiency reaches 94%. Such performance is much better than that of the conventional optimal H-plane horn antenna. [ABSTRACT FROM AUTHOR]

A novel full-digital multibeam array with wide scanning angle and enhanced beam gain is proposed for millimeter-wave massive multiple-input multiple-output applications. The array consists of 16 dual exponentially tapered slot antenna (DETSA) elements. Each element is integrated with a radio frequency receiver, an intermediate frequency chain, and an analog-to-digital converter (ADC). The H-plane radiation pattern of the proposed DETSA is very wide to enable the beam scanning in the azimuth plane. The beam gain is further enhanced by employing a 1-D multilayered planar lens that transforms the spherical wave into a plane wave in the E-plane for increasing the beam gain and keeping the phase compensation unaltered in the H-plane. Meanwhile, the planar lens is optimized to guarantee the wide scanning angle. In addition, all the signals received by the 16 independent channels are converted to a digital signal via ADC simultaneously and then used for synthesizing the multibeam patterns in the digital domain. Furthermore, the calibration and the verification of the synthesizing weights are discussed in detail. The measured results show that a scanning coverage of ±40° in the H-plane (or in horizontal plane) and an estimated maximum gain of 24.8 dBi with a gain tolerance of 3 dB can be achieved by the proposed 16-element array with a 1-D lens. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile and wideband metamaterial-lens (metalens) antenna based on high-refractive-index metasurface. A novel three-layer nonresonant metamaterial unit cell is introduced and analyzed by the full-wave simulation tool. The proposed unit cell is a stacking configuration of four H-shaped lines realized by multiple microwave laminates. It can achieve a large refractive index variation range of 4.76 (from 1.5 to 6.26). In addition, two impedance matching layers based on the proposed unit cell are developed to provide better transmission for incident waves passing through the metalens antenna. The attractiveness of this new metalens antenna is its low-profile thickness of $0.26~\lambda _{0}$ , where $\lambda _{0}$ is the wavelength at 10 GHz. To validate the performance of the metalens antenna, a wideband stub-loaded horn antenna with stable radiation patterns in E- and H-planes is adopted as the feeding antenna source. The measured results demonstrate a wide impedance bandwidth of 66% (7.2–14.3 GHz) and a high aperture efficiency of up to 65%. Moreover, its sidelobe and cross-polarization levels are less than −17 and −25 dB across the entire bandwidth, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this article, a dual‐polarized lens antenna system based on isotropic Huygens’ surfaces is proposed for 12 GHz applications. The surface lens is composed of subwavelength metallic patches etched on a 2‐layer dielectric substrate, which can realize high transmission efficiency and large phase shift (covering 0°–360°) over a wide bandwidth (11.0–13.0 GHz). The multimode resonances in the unit cell are detailed analyzed. The feed antenna at the focal point of the lens is a broadband dual‐polarized microstrip antenna. Both the simulated and measured results demonstrate that the dual‐polarized lens antenna system can realize the input ports isolation of more than 25 dB, and the gain of more than 17.0 dB. [ABSTRACT FROM AUTHOR]

This paper demonstrates a terahertz wideband antenna with Quartz hemisphere lens. The antenna has wide impedance bandwidth of 100%, −58.7 dB minimum return loss, high average radiation and total efficiencies of 89.7% and 88.4% respectively. Maximum gain of 13.2 dB is achieved at 1120 GHz. The antenna radiation pattern is shown at nine frequencies which represents steady pattern and main lobe direction. Finally we provide a comparison between the antenna and some main previous works. [ABSTRACT FROM AUTHOR]

A rotationally symmetric all-dielectric lens antenna is designed by defining the phase function inside the dielectric directly via a closed-form series formula. The refractive index of the lens is modified using state-of-the-art optical path rescaling to keep the refractive index within practical values. The lens optimization is done using the genetic algorithm in MATLAB, where each case is evaluated by conducting linked ray tracing and full-wave electromagnetic simulation in COMSOL. A lens prototype is shown to provide a directivity enhancement of 5.1 dB compared to the optimal conical horn antenna, an improvement of 2 dB compared to the Luneburg lens, and an improvement of 3.8 dB compared to a reference graded index lens. All the examined cases shared a similar length of 5 λ for the center frequency of 10 GHz. The prototype lens antenna has a maximum refractive index of 2.1, a reflection coefficient of −22 dB, and a side-lobe level of −25 dB at the center frequency of 10 GHz. The lens' performance is consistent in the 9–11 GHz band supported by the standard circular waveguide. The results from a prototype with a discretized refractive index simulated in CST Studio Suite are in excellent agreement with the ones with a continuous refractive index profile simulated in COMSOL. [ABSTRACT FROM AUTHOR]

A hybrid full-wave/quasi-optical electromagnetic model for the design of lens-integrated THz antennas for high frequency non-contact device characterization (30 GHz - 3 THz) is presented. Experimental validation of the antenna properties (input impedance and radiation pattern) is also provided to demonstrate the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]