A compact metasurface-based antenna is proposed for dual-band operations. The proposed metasurface is designed on a single-layered substrate including an array of modified <inline-formula> <tex-math ...notation="LaTeX">3 \times 3 </tex-math></inline-formula> squared patches. Each of the four corner patches is split into four fractional patches while the four edge patches are evolved into Malta crosses and the center patch is scaled. A substrate integrated waveguide-based Y-junction cavity-fed dual slot drives the metasurface with multiple impedance resonances. Based on the predicted modal behaviors of metasurface using a characteristic mode analysis (CMA), as an example, an antenna operating at three resonant modes at 28, 33, and 36 GHz, respectively is designed for the dual-band operation for the coming 5G. The proposed design shows that the measured impedance bandwidths (return loss larger than 10 dB) are 23.7-29.2 GHz and 36.7-41.1 GHz with the achieved gain of 4.8-7.2 dBi and 8.9-10.9 dBi, respectively. The proposed dual-band antenna features the advantages of low profile and wideband, suitable for the coming dual-band 5G applications.
A double-layered Huygens' unit cell is proposed to design a broadband metasurface lens (meta-lens) for 5G millimeter-wave antennas. The Huygens' unit cell consists of a pair of antisymmetric ...conducting semicircle arc elements on both surfaces of a thin dielectric substrate. The surface currents flowing at the opposite directions on both conducting elements form an electric current loop to induce the orthogonal magnetic current, and then the Huygens' resonances are stimulated. The Huygens' unit cell provides the transmission phase coverage of over 400° with transmission amplitude better than −2.3 dB. This breaks through the phase shift limitation of a conventional double-layer frequency-selective surface (FSS) element. It shows that induced magnetism makes such a Huygens-based meta-lens very compact with only one printed circuit board. As an example, a double-layered meta-lens on a 1.5 mm-thick dielectric substrate is designed and experimentally verified. The meta-lens antenna achieves the measured peak gain of 30.7 dBi at 26.2 GHz with an aperture efficiency of 42.25% over the 3 dB bandwidth of 15.7% from 24.1 to 28.2 GHz, fully covering the proposed 5G spectrum from 24.25 to 27.5 GHz. This proposed method greatly helps in the application of promoting planar lightweight low-cost broadband lens antennas in the coming 5G systems.
A shared-surface dual-band antenna is proposed for 5G operation using characteristic mode analysis (CMA). The surface is the integration of a metasurface at the S-band and a partially reflective ...surface (PRS) at the Ka-band. The resonant mode of the metasurface is excited by a microstrip-fed slot, and the PRS with a pair of substrateintegrated waveguide (SIW)-fed slots are employed to form a Fabry- Perot resonator antenna (FPRA). Measurements realized on a physical prototype of the antenna show a 10 dB impedance bandwidth of 23.45% and 9.76% and a realized gain that varies from 7.27 to 10.44 dBi and from 11.8 to 14.6 dBi, over the S-band (3.2-4.05 GHz) and the Ka-band (26.8-29.55 GHz), respectively.
Based on a transformation optics method, a flat compact dual-polarized Luneburg lens antenna is proposed and implemented using the printed-circuit-board-stacked gradient-index metamaterials for ...beamscanning and multibeam applications at X-bands. The transformed material properties of the planar Luneburg lens are designed with 17-layered permittivity distribution of polynomials. Each layer is discretized into <inline-formula> <tex-math notation="LaTeX">41 \times 41 </tex-math></inline-formula> pixels made of broadband and less polarization-dependent unit cells responsible for desired index distributions. The effects of transformation, approximation, and discretization on the lens performance are analyzed comprehensively. Also, to validate the implementation method, a flat Luneburg lens with a thickness of 14.1 mm, a focal length of 28 mm, and an aperture size of <inline-formula> <tex-math notation="LaTeX">98.9 \times 98.9 </tex-math></inline-formula> mm 2 is designed and tested. A stacked aperture-coupled patch antenna operating at 10 GHz is applied as a feeder. The measured results show that the proposed antenna can operate over a bandwidth of ~20% with an antenna efficiency of 32%, a cross-polarization level of <−17.1 dB, as well as the maximum gain of 15.9/16.35 dBi and a scanning angle of ±32°/±35° for two orthogonal polarizations, respectively. The presented flat Luneburg lens antenna featuring broad bandwidth, high gain, wide scanning angle, and easy fabrication has a high potential in 5G wireless communication, imaging, and remote sensing applications.
A metasurface (MTS) antenna is proposed for low-profile and wideband operation based on characteristic mode analysis (CMA). An MTS radiator formed by a diamond-slotted patch is fed by a microstrip ...line at its bottom through a slot centered on a ground plane. The CMA is used for the modeling, analysis, and optimization of the proposed antenna in order to reveal the underlying modal behaviors of the MTS and to guide the mode excitation. It is found that an extraordinary quisiTM30 MTS mode and a slot mode both with wideband broadside radiation are formulated and well excited simultaneously, leading to a broadband operation. Empirical equations are outlined for speeding up design. To verify the concept, a 2 × 2 array with the overall size of 1.78λ 0 × 1.78λ 0 × 0.07λ 0 (λ 0 is the free-space wavelength at 5.5 GHz) is designed and prototyped at 5-GHz Wi-Fi bands. The achieved impedance bandwidth for 10-dB return loss is 31% with the gain of 13-14.5 dBi over the operating bandwidth.
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 spherical incident waves to plane waves with its unit cell covering 360° transmission phase shift, while the transmittance remains higher than −1 dB. Both the metasurfaces are with symmetrical structures for dual-polarization. By integrating the amplitude and phase controllable metasurfaces, a <inline-formula> <tex-math notation="LaTeX">9.7\lambda _{0} \times 9.7\lambda _{0} </tex-math></inline-formula> metalens operating at 28 GHz 5G bands is designed and successfully suppresses the SLL. Within the 3 dB gain bandwidth from 26.0 to 29.0 GHz, this metalens antenna achieves the SLL lower than −20.9 dB in H-plane and lower than −17.3 dB in E-plane. The maximum gain is 23.4 dBi at boresight, and the achieved SLL is −16.3 dB as its scanning angle reaches the maximum of ±29°. Compared with the phase-only metalens, the proposed metalens antenna realizes the maximum and minimum SLL suppression of 9.8 and 3.4 dB within the 3 dB gain bandwidth at a price of a gain drop of 0.8 dB at the designed frequency.
An <inline-formula> <tex-math notation="LaTeX">{S} </tex-math></inline-formula>-/<inline-formula> <tex-math notation="LaTeX">{K} </tex-math></inline-formula>-band metasurface-based antenna with a ...shared aperture is proposed for 5G applications. The metasurface is designed with the dual-band characteristics for two antennas to work in the same aperture without interference. Based on the characteristic mode analysis, <inline-formula> <tex-math notation="LaTeX">3\times 3 </tex-math></inline-formula> metasurfaces are proposed for the <inline-formula> <tex-math notation="LaTeX">{S} </tex-math></inline-formula>-band radiation. To radiate the <inline-formula> <tex-math notation="LaTeX">{K} </tex-math></inline-formula>-band electromagnetic wave without blocking, the metasurfaces are discretized by the subcell of a square ring and an inner square patch to achieve a frequency selective function. Then, as an example, the microstrip-fed slot is used to drive the metasurfaces at the <inline-formula> <tex-math notation="LaTeX">{S} </tex-math></inline-formula>-band, while an <inline-formula> <tex-math notation="LaTeX">8\times 8 </tex-math></inline-formula> substrate integrated waveguide slot array antenna between microstrip and metasurface is designed at the <inline-formula> <tex-math notation="LaTeX">{K} </tex-math></inline-formula>-band. The measurement shows the 10 dB return loss bandwidths of 23.45% and 4.8% and the realized gain of 7.52-10.88 and 21.3-22.4 dBi over the <inline-formula> <tex-math notation="LaTeX">{S} </tex-math></inline-formula>-band (3.2-4.05 GHz) and the <inline-formula> <tex-math notation="LaTeX">{K} </tex-math></inline-formula>-band (25.22-26.46 GHz), respectively.
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 (cDCGAN) is utilized in the proposed deep-learning (DL) method. Prior knowledge, including well-known fundamental electromagnetic theorems and experience in antenna design, is purposely applied at the early stage of the proposed method to strategically guide and speed up the synthesis. The proposed intelligent method provides the design of pixelated metacells with high degrees of freedom so that the key performance of the synthesized metacells exceeds the existing limit of conventional design methods by generating a rich profusion of cell patterns. For example, the synthesized triple-layer metacell achieves the −1 dB phase shift range of 330° breaking the limit of 308° derived by existing techniques. The proposed synthesis method also provides the additional capability to flexibly control the phase shift not only at the center frequency but also over a frequency range of interest. A Ku-band metalens antenna formed with the synthesized metacells demonstrates the achieved 1 and 3 dB gain bandwidths increase by 52.2% and 42.6%, respectively, compared to the metalens antenna using the well-known Jerusalem cross (JC) metacells. The proposed method extends the capability for the synthesis of metacells and metalens antennas with enhanced performance.
A vertically polarized substrate-integrated waveguide (SIW)-fed endfire metasurface antenna array is proposed for wideband operation. Each of the metasurfaces consists of <inline-formula> <tex-math ...notation="LaTeX">3\times 3 </tex-math></inline-formula> rectangular patches and is printed on the two surfaces of a single-layered substrate with a thickness of <inline-formula> <tex-math notation="LaTeX">0.16\lambda _{0} </tex-math></inline-formula> (where <inline-formula> <tex-math notation="LaTeX">\lambda _{0} </tex-math></inline-formula> is the wavelength at 32.65 GHz in free space). The antenna is fed at one side of metasurface by an open-end SIW for wideband endfire radiation. The proximity-coupled interdigital strips are introduced between the SIW and metasurface for fault-tolerant coupling. The wideband operating mechanism is revealed by studying the propagation mode and multiple resonant modes of metasurface. To verify the proposed antenna, a <inline-formula> <tex-math notation="LaTeX">1\times 4 </tex-math></inline-formula> array is presented with uniform excitation including two SIW Y junctions and an SIW T junction. Moreover, the connected SIW Y junction improved the impedance matching at the low frequencies based on the cavity mode analysis. The proposed design shows that the measured impedance bandwidth (10 dB return loss) is 26.6-38.7 GHz (37%) with the achieved gain of 9.1-13.8 dBi.
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 ...<inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula>-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.
