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This work presents a novel design of a low-profile broadband circularly polarized (CP) metasurface (MS) antenna based on characteristic mode analysis (CMA) technique for potential use in C-band satellite communications. The proposed antenna is composed of a 4 × 4 array of truncated patch unit cells and incorporates an enhanced slot coupling feeding structure. CMA technique is employed to analyse and modify to improved CP performance. The proposed design exhibits good radiation characteristics including measured − 10 dB impedance bandwidth of 22.72% (4.8–6.05 GHz), a 3 dB axial ratio bandwidth (ARBW) of 16.3% (5.1–5.95 GHz), and a peak gain of 8 dBi within its operational frequency range. Furthermore, the antenna's metasurface design contributes to scattering suppression over a wide frequency span (4–18 GHz), with a notable peak reduction of 9.1 dB at 8 GHz. This characteristic holds potential significance for radar cross-section (RCS) reduction. [ABSTRACT FROM AUTHOR]

This communication presents a wideband and a low-profile flexible wearable antenna intended to operate at a 2.45 GHz WBAN band. The suggested antenna comprises a CPW-fed monopole antenna backed by an artificial magnetic conductor (AMC) to act as a reflector. The latest AMC-integrated design uses R03003 as a dielectric substrate. The suggested design features an impedance bandwidth of 71.03% (1.87–3.93 GHz) with a gain value of 3.62 dBi and has a compact footprint of 40 × 40 mm2. The incorporation of wideband AMC with a monopole antenna leads to bandwidth enhancement and covers the 3.5 GHz WiMAX band. Simulation and experimental studies provide evidence that in the case of structural deformities and human body loading, the suggested AMC-integrated antenna is stable and shows superior efficiency relative to the traditional monopole antenna. Furthermore, numerical analysis demonstrates that the amount of radiation AMC-integrated antenna decreases tremendously in terms of specific absorption rate for various bodily attachment scenarios. Three body templates with various compositions and forms were used to study the effects of the antenna on bodily attachment. Extensive experiments on human body phantoms and bodily attachment are also conducted and the results are presented. The suggested AMC-integrated design thus confirms a promising contender for portable wearable wireless applications. [ABSTRACT FROM AUTHOR]

This letter presents the design principle and experimental verification of a Ku‐band wideband low‐profile dual‐circularly polarized (dual‐CP) reflectarray (RA) with independent control of left‐/right‐handed circularly polarized (LHCP/RHCP) beams. Both the dynamic phase (DP) and Berry phase (BP) compensating methods are employed in the design of the unit cell, achieving independent LHCP/RHCP phase modulation based on the single‐functional‐layer concept. A single‐layer unit cell is designed, offering a 3×3 $3\times 3$‐bit dual‐CP phase shift which facilitates the independent control of LHCP/RHCP beams. A prototype with asymmetrical dual‐CP beams is fabricated and tested. For LHCP and RHCP excitation, beam directions of (120∘,10∘ $12{0}^{\circ },1{0}^{\circ }$) and (135∘,−30∘ $13{5}^{\circ },-3{0}^{\circ }$) are realized, respectively, with sidelobe levels and cross‐polarizations both under −15 dB. The prototype exhibits a wide axial ratio (AR) bandwidth of over 36% with AR <2 $\lt 2$ dB. The overlapped 1‐dB gain and AR <2 $\lt 2$ dB bandwidth is 19.5% under LHCP input and 12.2% under RHCP input, with maximum aperture efficiency of 41.3% and 34.6%, respectively. The proposed dual‐CP RA exhibits broad band, pure chirality, high gain, low profile and independent polarization control, with single‐layer construction which is of low cost and easy processing. [ABSTRACT FROM AUTHOR]

In this letter, a wideband and low‐profile multipolarization reconfigurable antenna based on metasurface (MTS) is proposed. The antenna mainly contains two parts, an upper layer of MTS and a bottom layer of circular slot antenna. The MTS acts as a polarization controller, by mechanically rotating the MTS layer at a proper angle while keeping the circular slot antenna remain stationary, the polarization mode of the antenna can be switched to linear polarization (LP), left‐hand circular polarization (LHCP), and right‐hand circular polarization (RHCP). The experimented −10 dB impedance bandwidth of 37.8% and 54% for LP and circular polarization (CP) modes, respectively. The measured overlapped 3‐dB AR bandwidth is 22.2% for both CP modes, covering from 3.2 to 4 GHz. Moreover, the measured peak gain of the presented antenna reaches 9 dBi and 8 dBic for LP and CP modes, with a lower profile of 0.05 λ0. [ABSTRACT FROM AUTHOR]

In this article, a low profile wideband metasurface filtering antenna with tunable radiation nulls is proposed. Metasurface structure is used to excite adjacent resonant modes to obtain broadband responses. A U‐shaped slot is introduced into the microstrip line to generate a radiation null in the lower stopband. Complementary split‐ring resonators (CSRRs) are etched on the metasurface unit to produce another radiation null in the upper stopband edge to improve the filtering effect. The radiation nulls position can be flexibly controlled by changing the size of U‐shaped slot and CSRRs. For verification, the corresponding antenna is fabricated and tested. The antenna size is 0.556λ0×0.556λ0×0.044λ0 (30 × 30 × 2.4 mm3). The measured results agree well with the simulated. The antenna operates from 4.9 to 6 GHz with a flat gain (5.5 dBi), a sharp passband skirt and stable radiation patterns. [ABSTRACT FROM AUTHOR]

To suppress mutual coupling among multiple-input multiple-output (MIMO) stacked patch antennas, a decoupling method achieving three mutual coupling nulls is proposed by utilizing one pair of symmetrical half-wavelength strips and a dual-hole single-pad structure. The first two mutual coupling nulls are caused by path cancellation after utilizing the two half-wavelength strips. The third one is triggered by phase cancellation of the driven and parasitic patches, and can be controlled by the dual-hole single-pad structure. Compared with the reported decoupling designs on stacked patch antennas, the proposed one can achieve wider decoupling bandwidth, higher isolation improvement, and no profile enhancement. The mutual coupling level of the two-element stacked patch antenna integrated with the proposed decoupling method can be decreased from −21.5 dB to −36.5 dB over the effective frequency range from 3.28 GHz to 3.6 GHz or 9.3%. Afterward, the proposed method is also proved to be effective in four-element stacked patch antenna. [ABSTRACT FROM AUTHOR]

In this article, we present the design of a low-profile circularly polarized (CP) magneto-electric (ME) dipole antenna with enhanced CP bandwidth properties. The ME dipole antenna is excited by a simple microstrip line aperture-coupled feeding structure. The coupling aperture is composed of two crossed slots of unequal lengths to realize CP operation. Four identical inverted $L$ -shaped parasitic elements, each consisting of a horizontal patch and a vertical metallic plate, are vertically positioned around the ME dipole. It was found that such parasitic elements can remarkably improve the 3 dB axial ratio (AR) bandwidth while retaining the wide impedance bandwidth. A prototype with a low profile of only $0.134\lambda _{L}$ ( $\lambda _{L}$ is the wavelength in free space at the lowest operating frequency) is fabricated and tested to verify the proposed design. The experimental results show that the prototype has an overlapping impedance bandwidth ( $|S_{11}| \leq -10$ dB) and a 3 dB AR bandwidth of 3.16–5.36 GHz (51.35%) with a maximum broadside left-handed CP gain of 9.75 dBic. Additionally, nearly identical radiation patterns on two principle cutting planes are obtained over the operating band.

A wideband 1 bit reconfigurable transmitarray antenna (RTA) with low-profile characteristic is presented. First, a wideband element for the RTA is designed by combining two centrally fed magnetoelectric (ME) dipoles. Two p-i-n diodes are integrated within the element to achieve 1 bit reconfigurable phase states. Next, the folded scheme is adopted to achieve multiple reflections between the feed source and the RTA, and thus, the height-to-diameter ratio (H/D) is reduced to about one-third of that of the conventional transmitarray. A reflective surface with polarization conversion function is designed beneath the RTA around the source, the unit cell of which is a special $C$ -shaped polarizer operating over a wide frequency band. Finally, a low-profile RTA with $12 \times \mathbf {12}$ elements is designed, fabricated, and measured. The whole structure has an aperture size of $\mathbf {5}.\mathbf {75} \boldsymbol {\lambda }_{\mathbf {0}}\times \mathbf {5}.\mathbf {75} \boldsymbol {\lambda }_{\mathbf {0}}$ , and H/D is 0.28. Measured results show that the proposed RTA has the beam-scanning capability to $\pm \mathbf {40}^{\circ }$ in both E- and H-planes over a bandwidth of 32%. The realized gain is up to 19 dBi and the peak aperture efficiency is 20.5%. [ABSTRACT FROM AUTHOR]

A low-profile, wideband dual-polarized 1 × 2 multiple-input-multiple-output (MIMO) antenna with frequency selective surface (FSS) decoupling technique is presented. Low profile is realized with two different artificial magnetic conductor (AMC) cells out of which one operates at 3.5 GHz and other with dual band at 3.1 and 4.5 GHz. The proposed antenna height is maintained at 0.125λ0 which is significantly reduced when compared with the conventional perfect electric conductor (PEC) ground plane. Wideband dual polarization is enabled by two pairs of bow-tie antenna elements surrounded by a square ring placed in the orthogonal orientation. To mitigate the near-field coupling in 1 × 2 MIMO an FSS wall is constructed with wide band stop characteristics from 2.85 to 4.75 GHz. Measured results show by inserting FSS wall vertically, coupling reduction is improved by 27 dB over the existing coupling and the antenna exhibits a bandwidth of 57.14% (2.95–4.95 GHz) for VSWR<2 with port isolation of more than 25 dB for entire band of operation. [ABSTRACT FROM AUTHOR]

A millimeter‐wave (mm‐wave) dual‐polarized antenna achieved by stacking single patch and 2 × 2 patches with square holes is proposed to achieve low profile and wide bandwidth. The single patch and the 2 × 2 patches operate at two pairs of orthogonal modes, TM10/TM01 modes and antiphase TM20/TM02 modes, respectively. The square holes are introduced to adjust the coupling between the two layers of patches with small spacing. The appropriate coupling between two layers of patches and the low quality factor of the upper 2 × 2 patches make the proposed antenna achieve wide bandwidth with relatively low profile. A pair of perturbation slots is introduced to adjust the port‐to‐port isolation. The characteristic mode analysis (CMA) method is utilized to analyze the antenna element to reveal the modal behavior of the proposed antenna. For demonstration, a prototype of 2 × 2 array with a profile of 0.05λ0 (λ0 is the wavelength in free space at the center frequency) is designed and fabricated, which achieves the measured 10‐dB bandwidth of 24.5%, the maximum gain of 11.6 dBi, and the port‐to‐port isolation of 23.5 dB. [ABSTRACT FROM AUTHOR]

In this paper, a novel low-profile magnetoelectric (ME) dipole antenna with wideband is presented. The conventional vertical fixing structure is bended four times from the center to the sides. The Γ-shaped feeding structure is bended two times to lower the height of the antenna step by step. The effect of three kinds of vertical wall is discussed to show their influence on boresight gain. Through comparison, only one vertical wall is erected on the left side of the ground to decrease the boresight gain drop at 2.2 GHz. Both simulation and analysis are made to sufficiently explain the working principle. At last, the proposed ME dipole antenna has only 0.095λ0 (λ0 is the center operating wavelength in free space) in height, and the wideband property is still maintained. By simulation, the relative bandwidth for VSWR < 2.0 is 47.9% (from 1.35 to 2.2 GHz). The boresight gain ranges from 8.1 to 9.6 dBi in the operating band. The measured relative bandwidth for VSWR < 2.0 is 50.3% (from 1.34 to 2.24 GHz), and the boresight gain ranges from 7.38 to 8.73 dBi. The gain drop on boresight is less than 1.4 dBi. Radiation patterns show a unidirectional characteristic in the whole operating band. Additionally, the cross-polarization level is less than −25 dB on boresight. The simulating and measuring results agree well with each other. Therefore, the proposed antenna is suitable for applications of limited height and wideband. [ABSTRACT FROM AUTHOR]

A wideband dual-polarized high-efficiency transmitarray antenna utilizing the isolated metal elements is proposed. First, a dual-polarized isolated metal element supported by a substrate frame is introduced. Each array element is isolated from adjacent elements by gaps. To realize the element, a substrate frame is used to completely fill the gaps and support the elements. As a result, the limitation of metal connections is overcome, and the transmitarray bandwidth is significantly enhanced. Based on equivalent circuit of the element, its wideband operating mechanism is revealed. Then, to reduce the manufacturing difficulties and costs while maintaining electrical performance, PCB technology is applied to the transmitarray fabrication, integrating the elements and the substrate frame. Finally, a wideband dual-polarized substrate-based metal transmitarray is designed, fabricated and measured. The measured results of the prototype indicate that its gain at the center frequency 10.2 GHz is 26.9 dBi, its 1-dB gain bandwidth is 23.4%, its efficiency is 56.1% and its lowest efficiency across the 1-dB gain bandwidth is 38% at 12.4 GHz. To the best of our knowledge, this is the first time a wideband two-layer substrate-based metal transmitarray has been proposed and implemented. [ABSTRACT FROM AUTHOR]

A Ka-band dual-polarized low profile magneto-electric (ME) dipole antenna with wide operational bandwidth is proposed in this paper. A thin substrate with two-stage meandered vias is utilized for realization of the proposed antenna. The meandered vias aid in compensation of phase difference caused due to utilization of thin substrate. The thickness of proposed antenna is reduced from 0.25 λg to 0.11 λg by using these two-stage meandered vias. The low profile antenna topology results in bandwidth reduction which is neutralized by introducing asymmetric slots in the ground plane. Shorting pins are inserted for elimination of higher order TM21 mode of Ka-band that results in a uniform broadside radiation pattern due to excitation of fundamental TM10 mode. The proposed antenna covers whole Ka-band with operating frequencies from 26 - 42 GHz. A 1 × 4 antenna array is also designed and fabricated with a reasonable gain of 12.06 dBi and stable radiation patterns. Simulated and measurement results are presented with detailed justification.

This paper presents a low-profile magneto-electric (ME) dipole antenna with an enhanced impedance bandwidth realized by the loading of shorting parasitic elements. The antenna contains a horizontal planar electric dipole antenna, a $\Gamma $ -shaped shorted patch antenna, a pair of parasitic L-shaped shorted patches, and a direct feed. By loading of the parasitic L-shaped patches such that they are shorted to the ground, the proposed antenna attains a significant bandwidth enhancement while maintaining excellent broadside radiation characteristics. An antenna prototype with a low profile of only $0.11\lambda _{0}$ was fabricated and tested ( $\lambda _{0}$ is the free-space wavelength referring to the center frequency). The antenna achieves a measured impedance bandwidth of 75.64% (1.34–2.97 GHz) for a voltage standing wave ratio (VSWR) of less than 2. Within the operating band, the measured gain ranges from 6.23 to 8.49 dBi. Additionally, stable radiation patterns on both E- and H-planes with a high front-to-back ratio of more than 20.5 dB are achieved.

In this letter, a novel dual-mode slot-patch antenna is proposed in the Ka-band. Resonant modes of a slot and four patches are merged for widening the bandwidth of the low-profile antenna that is fed by an open-ended substrate integrated coaxial line. The design with a profile of 0.05λ0 achieves a wide bandwidth of 27.5% and stable unidirectional radiation patterns. Based on the proposed antenna, a 1 × 8 array with an unequal power feeding network is designed and measured, which demonstrates an impedance bandwidth of 23%, a gain of up to 15.4 dBi, and the sidelobe level of lower than −18 dB. Benefitted from the desirable geometric and operating characteristics, the presented slot-patch antenna is suitable for 5G millimeter-wave applications. [ABSTRACT FROM AUTHOR]

A broadband low-profile folded transmitarray (FTA) is proposed and investigated, in which a novel wideband transmission polarizer (TP) is used to realize low-profile design. The proposed TP, mainly consisting of a differential-fed grid-slotted patch antenna, can realize high-efficiency transmission and polarization selection simultaneously within a wideband frequency range. Moreover, the proposed TP can realize linear transmission phase because of the true-time delay (TTD) technique. Owing to the function of polarization selection and linear transmission phase, the TP can be used as antenna element for a FTA. A 140-element FTA is designed and fabricated by combining the TP with a broadband polarization rotation reflecting surface (PRRS). The measured radiation patterns agree well with the simulated results, and a peak gain of 24 dBi and maximum aperture efficiency of 44.7% are achieved. Furthermore, −1 and −3 dB gain bandwidth with 25.9% and 33.3% are also experimentally demonstrated in the proposed FTA, respectively. [ABSTRACT FROM AUTHOR]

A dual‐polarized microstrip patch antenna array is designed, constructed, and measured. The patch array is compactly arranged through the design of a suitable series–parallel hybrid feed network. The antenna array demonstrates the bandwidth (10 dB return loss) of port 1 and port 2 are 13.8% (5.41–6.21 GHz) and 9.7% (5.5–6.06 GHz) in measured results respectively. The antenna maintains −27 dB cross‐polarization level in the operating band, whereas the isolation for the two orthogonal ports is 39 dB and more. In addition, the antenna array prototype achieves average gains of 13.5 dBi for horizontal and 13.9 dBi for vertical polarizations, respectively. Moreover, the profile of the array is very low based on the proposed antenna unit with a low profile of 3.1 mm (0.06 λ0 at 5.8 GHz), which is a microstrip‐fed dual‐polarized antenna. [ABSTRACT FROM AUTHOR]

In this article, a multilayered substrate‐integrated magnetoelectric dipole antenna with low profile and wideband is proposed. Based on the multilayered printed circuit board technology, the magnetoelectric dipole antenna is composed of four layers of substrate. By adopting rectangular window techniques, the impedance matching at the low‐frequency band is improved and a low profile of 0.08λ0 (where λ0 is the free space wavelength of the center frequency) in height is achieved. A Γ‐shaped meandering unit is also adopted to guide the electric current through the rectangular window and enhance the boresight radiation. Additionally, the antenna is fed by a 1/4 wavelength microstrip line on bottom plane to easily integrate to the front‐side planar circuit. The transverse size of the proposed antenna is 100 mm*50 mm (0.8λ0*0.4λ0). Through simulation and optimization, the wideband, low profile, and unidirectional radiation characteristics are obtained simultaneously. The tested impedance bandwidth ranges from 1.92 to 3.15 GHz (48.5%) for voltage standing wave ratio (VSWR) < 2. The radiation property is also validated and the boresight mean gain is 5.1 dBi. Cross polarization level at boresight is lower than −25.15 dB. Both simulated and tested results agree well with each other. [ABSTRACT FROM AUTHOR]

A low-profile DRA employing dielectric and air vias is investigated. The structure is realized utilizing PCB technology only. The dielectric vias are formed by filling up cylindrical holes with barium strontium titanate (BST) nanoparticles with a dielectric constant of 20 and a loss tangent of 0.023. Using this technique, the antenna can be made compact, without the need for using external, high dielectric-constant materials that are unavailable for standard PCB manufacturing. By skillfully arranging air vias inside the DRA, the resonant frequencies of different modes can be controlled, and a wide impedance bandwidth with stable radiation performance can be achieved. The whole antenna structure can be manufactured using standard PCB materials and manufacturing technologies. Our prototype achieves a wide measured impedance bandwidth of 47.5% and a maximum measured gain of 6.84 dBi. Furthermore, a small antenna footprint of $0.616\times 0.616\,\,\lambda _{0}^{2}$ with a low profile of $0.095~\lambda _{0}$ is achieved, where $\lambda _{0}$ is the wavelength in the air at the center frequency. A dual-polarized antenna is investigated using this design technique. It achieves an overlapping bandwidth of 34.88% of its two ports with isolation of higher than 25.76 dB and stable radiation performance across the passband. [ABSTRACT FROM AUTHOR]

A wideband circular patch antenna (CPA) is proposed and fabricated in this article. Based on the cavity mode theory of circular patch, four resonant modes of quasi-TM01, quasi-TM02, quasi-TM03, and quasi-TM04 are merged together to obtain a wide passband through cutting slots and adding short pins on the driven patch. In order to generate low stopband radiation nulls, two circles of defected ground structures (DGSs) are designed. Meanwhile, a stacked patch is added above the driven patch to obtain an upper edge radiation null. The experimental results achieve the 10 dB impedance bandwidth of 30.3% from 5.3 to 7.19 GHz with an overall size of $1.84\,\,\lambda _{0} \times 1.84\lambda _{0} \times 0.05 \lambda _{0}$ ($\lambda _{0}$ is the free space wavelength at 6 GHz). Without any extra filtering circuit, the proposed antenna obtains the sharp band edge with a stopband suppression level of 15.7 dB. The out-of-roundness of the radiation pattern in the H-plane is less than 2.7 dB in passband. With good performance in wideband, omnidirectivity, low profile, and high stopband suppression, the proposed antenna has great application prospects in the high-integration microwave systems of large unmanned aerial vehicles. [ABSTRACT FROM AUTHOR]

We use indium tin oxide (ITO), one of the representative resistive materials, for the implementation of a metamaterial electromagnetic (EM) absorber with a high absorbance in a wide frequency range. Highly symmetrical split ring resonators made of ITO film are deposited on the polyethylene terephthalate with transparent and flexible features, and such a configuration causes the proposed absorber to be insensitive to polarization and incidence angles. The proposed absorber, with a profile of only 0.171 λ , exhibits a wideband absorbance of 7.2 GHz to 27 GHz, with a 90% absorption criterion. A prototype is built, and all the computed expectations from the full-wave EM simulations in this work are verified experimentally. [ABSTRACT FROM AUTHOR]

An ultralow-profile circularly polarized (CP) reflectarray (RA) antenna is presented in this article, based on the variable-rotation technique for beam collimation and scanning. Starting from a conventional split-loop element, a new wideband element is designed having a single conductor layer on a single thin dielectric. The RA element, based on two coupled microstrip loops, exhibits a dual-resonant CP behavior and a stable response over a wide range of incident angles and frequencies. The wideband response is explained through eigenmode and full-wave simulations in an infinite-array environment, by examining the current distributions on the coupled loops. A high-gain 900-element offset-fed RA antenna is designed for CubeSat intersatellite links at 24.6 GHz using the proposed element. A new element rotation procedure is used to determine the required rotation angles, while eliminating phase errors in the RA aperture. The antenna prototype exhibits a 1 dB gain bandwidth of 6.8% and an axial ratio smaller than 1 dB, with the array profile of only 0.042 λ0 at 24.6 GHz. The maximum measured antenna gain is 31.5 dBi, which corresponds to a total aperture efficiency of 58%. [ABSTRACT FROM AUTHOR]

In this article, a low-profile and wideband circularly polarized patch antenna is proposed and developed, which is composed of the circular patch fed by four ports. A wideband property is achieved by utilizing TM11 and TM21 mode, as well as the orthogonal mode of TM11. The Γ-shaped feed is employed to stimulate the TM21 mode. Besides, due to the parasitic radiation from the face-to-face Γ-shaped feeds with opposite phase, the radiation peak of the circular patch under TM21 mode is along the broadside direction, which is different from the original radiation mechanism of TM21 mode. By loading shorting pins in the middle area of circular patch, the polarization orthogonal mode of the fundamental mode (TM11) is excited properly, which contributed to bandwidth enhancement. Cooperated with the quadrature phase feed network, a wideband circular patch antenna with unidirectional radiation and circular polarization properties is designed, fabricated, and measured. The size of the circular patch is 0.57λ0 × 0.57 λ0 and the height is only 0.053λ0 (λ0 is the free space wavelength at the center frequency). The measured results show that the 109% of fractional bandwidth is obtained under the condition of VSWR < 2, ranging from 0.94 to 3.18 GHz, and the 3 dB axial ratio fractional bandwidth is 95%, ranging from 1.04 to 2.93 GHz. Besides the realized LHCP gain >3 dBic from 1.27 to 2.99 GHz. [ABSTRACT FROM AUTHOR]

A novel wideband circularly polarized microstrip patch antenna (MPA) with multimode resonance is proposed in this letter. The TM1/2,0 mode, the zeroth-order mode, and the TM1,0 mode are excited by inserting the shorting pins underneath the driven patch and the parasitic patch. Therefore, a wide impedance bandwidth is achieved under triple-mode resonance. By sequentially rotating the triple-mode elements, a circularly polarized MPA is developed with a four-feed network. Additionally, four metallic side walls are employed to obtain desirable radiation performances. For demonstration, a prototype of the proposed antenna is fabricated and measured. The measured −10 dB impedance bandwidth is 96% (1.53–4.39 GHz) and 3 dB axial ratio bandwidth is 86% (1.74–4.36 GHz). Meanwhile, a low profile with the height of 0.037λ0 (λ0 is the wavelength in free space at the lowest operating frequency) is obtained. Such a wideband, low-profile, and circularly polarized antenna is very promising for modern wireless communication applications. [ABSTRACT FROM AUTHOR]

A double-layer highly efficient and wideband transmitarray antenna is presented. The transmitarray element is composed of four metal vias and two crosspatches with two stubs. The metal vias penetrate the entire substrate and arrange symmetrically. The crosspatches are printed on both sides of the dielectric substrate. The metal vias are introduced to enhance the coupling strength. The stubs are added to ensure a sufficient phase shift range. The achievable transmission magnitude is greater than -2 dB, and the phase shift range exceeds 360° within the whole band. A transmitarray antenna using the proposed element was designed, manufactured, and measured. The simulation and measurement results are in good agreement. The measured maximum gain is 29.2 dBi at 18 GHz with the 51.4% aperture efficiency. The experimental results show that the proposed antenna has a 1-dB gain bandwidth of 9% (17.2-18.8 GHz). The proposed double-layer transmittarray antenna realizes the low-profile characteristic, simplifies the design complexity, and solves the problems of the mass and the cost.

An efficient wideband polarization-rotation thin metasurface based on oval pattern is presented. The aim of this structure is to manipulate the polarization of incident electromagnetic waves in reflect band. The oval pattern is split by strip lines to outperform the results. It is shown that the proposed polarization converter converts the incident linearly or circularly polarized waves into orthogonal counterpart over a frequency band of 10.2–20.5 GHz. A prototype of the proposed structure is fabricated to validate the numerical simulation. The experimental and simulation results confirm that polarization conversion ratio (PCR) is greater than 90% at the same frequency band with high stability to oblique incidence angle. Numerical simulation reveals that the strong electric and magnetic resonances between top and bottom layers lead to wideband polarization conversion. Equivalent impedance surface method is discussed to further analysis the polarization conversion mechanism. [ABSTRACT FROM AUTHOR]

A novel wideband low‐profile antenna using a hybrid metasurface (MS) structure is presented. The proposed hybrid MS radiator consists of metal patches of different shapes or arrangements, and is fed by a microstrip line through a coupling slot etched on the ground plane. Several resonance modes can be excited for the hybrid MS radiator when a linearly polarized incident plane wave reaches, while one more resonance mode can be introduced by the coupling slot. As a result, wideband and stable radiation can be obtained. The results of the fabricated antenna prototype indicate a large bandwidth of 57.4% (5.23 ~ 9.44 GHz) and a stable gain with a 2‐dB gain bandwidth of 39.2% in a low profile of 0.09λ0. The performances are demonstrated by both simulated and experimental results. [ABSTRACT FROM AUTHOR]

A millimeter-wave (mmW) low-profile wideband magneto-electric (ME) monopole antenna with the vertically polarized endfire radiation is presented by combining a pair of the top-loaded electric monopoles with a thin open-ended substrate integrated waveguide (SIW) with the extended lower broad wall. The antenna has a profile of 0.19 wavelength at the center frequency of the operating band, a wide bandwidth of 60.7% (from 23.5 to 44 GHz) covering all the fifth-generation (5G) mmW bands in the Ka-band, a stable gain of around 7 dBi, and a tilted radiation pattern. Then a $1 \times 8$ ME-monopole array is designed to investigate the beam scanning properties and the effects of the metallic ground and the polycarbonate radome, which should be considered in practical applications. As a sample, a $1 \times 8$ array fed by an SIW feed network, assembled on a metallic ground plane, and covered by a polycarbonate radome is finally designed, fabricated, and measured. The prototype achieves promising radiation features with a gain up to 15.3 dBi. Owing to the compact low-profile structure with good performance, the proposed design would be valuable to the mmW applications. [ABSTRACT FROM AUTHOR]

A compact low-profile ultrawideband circularly polarized (CP) metasurface antenna (MSA) array is presented in this letter. The array consists of 2 × 2 sequentially rotated symmetric MSA elements and a wideband four-way feeding network providing stable phases of 0°, 90°, 180°, and 270°. By using the constructed feeding network and MSA element, the CP array can achieve an ultrawideband CP performance with a low profile of 0.05λL. The measured results show that the proposed MSA array achieves the 10 dB impedance bandwidth of 97.2%, 3 dB axial ratio bandwidth of 83.2%, and 3 dB gain variation bandwidth of 73.8%. Compared with the other designs in published literatures, the proposed CP MSA array owns the advantages of low profile with a simple structure and good CP performance without any air gap, thus indicating a promising candidate in compact wideband wireless systems. [ABSTRACT FROM AUTHOR]

A low-profile wideband metasurface antenna with quad-polarization reconfiguration ability is presented in this paper. The proposed metasurface antenna is composed of a square patch, a metasurface formed by a lattice of 4 × 4 periodic metal plates, and four switchable feeding probes connected with two designed single-pole double-throws switches. By properly selecting the feeding probes, the polarization of the metasurface antenna can be dynamically reconfigured among four polarization states, i.e., x-direction linear polarization, y-direction linear polarization, left-hand circular polarization, and right-hand circular polarization. To validate the proposed concept, a prototype operating at 5.6 GHz with a relatively height of 0.067 λ0 (λ0 is the operating wavelength in free space) is designed, fabricated, and measured. The measured results show that both the 10-dB impedance bandwidths and the 3-dB axial ratio bandwidths are wider than 5.1-6.0 GHz for the linear and circular polarization states. The measured maximum gains are 9.39 dBic and 9.85 dBi for the circular polarization states and the linear polarization states, respectively. The simulation and experimentation verify that the proposed antenna can achieve quad-polarization reconfigurable features in a wide frequency band, which indicate the good performance of the proposed polarization reconfigurable metasurface antenna.

In this paper, we propose a 4 × 4 low-profile wideband patch array antenna with radiation pattern agility. The digital-controllable antenna element is composed of a square driven patch, a 2×2 parasitic patch array, and two switchable feeding ports, which are connected to a designed single-pole double-throw switch. Due to the symmetrical structure, individual excitation at the two feeding ports produces a 1800 phase difference, giving rise to two basic digital elements of “0”and “1,”respectively. By switching the feeding ports for all antenna elements using a micro-controller unit, the radiation beam of the 4×4 array antenna can be dynamically reconfigured. To validate the proposed concept, a prototype operating at 5.7 GHz with an overall size of 3.42λ0 × 3.42λ0 × 0.069λ0(λ0 is the free-space wavelength at 5.7 GHz) was fabricated and measured. The measured 10-dB return loss bandwidths for all the states cover the frequency band of 5.12-6.32 GHz. The simulated and measured results show close agreement, which proves the powerful dynamical beam manipulation capability of the proposed array antenna.

A wideband small-footprint circularly polarized Fabry-Perot resonator antenna is presented in this paper. The design employs a partial reflecting surface (PRS) consisting of thin homogeneous dielectric slabs separated by a small air gap. The PRS is analyzed using transmission line theory, which gives more insightful into the theoretical concept and provides a simple tool for design and optimization. An antenna prototype with overall size of 1.2λfmin × 1.2λfmin × 0.6λfmin has been fabricated and experimentally validated (λfmin being the free-space wavelength at the minimum operating frequency). The measured impedance matching and axial ratio bandwidths are approximately 55.7% and 47.7%, respectively. In addition, the antenna achieved 3-dB gain bandwidth of 50.9% with a peak gain of 15 dBi. Compared to previous designs targeting similar applications, the antenna proposed here possesses a simple geometry with light weight, ease of optimization and fabrication, as well as enhanced axial ratio bandwidth and 3-dB gain bandwidth.

In this letter, a patch-driven low-profile broadband metasurface (MTS) antenna is proposed. The novel antenna is constituted utilizing an aperture coupled patch and proposed configurations of finite-sized artificial magnetic conductor. With the surrounding MTS excited by the surface wave introduced through the center patch, an additional TM resonance is generated and a wideband impedance matching is achieved. The performance and operating mechanism of the proposed antenna are investigated and analyzed. To demonstrate the concept, a 1 × 4 array with an overall thickness of 0.047 λ0 (λ0 is the free-space wavelength at 28 GHz) is successfully implemented through advanced substrate manufacturing process. The obtained impedance bandwidth for reflection coefficient below −10 dB is 27.1% with a maximum realized gain of 13.6 dBi. [ABSTRACT FROM AUTHOR]

A low-profile wideband dual-polarized antenna with an improved high-impedance surface (HIS) reflector is proposed. Dual-polarized radiation is excited by feeding a set of crossed dipoles. Low profile is achieved by utilizing an improved HIS reflector. Good impedance characteristics are realized by inserting small square cells among the primary hexagonal cells of the HIS. Two shorting pins and four parasites are introduced to increase port-to-port isolation and improve impedance matching, respectively. A prototype with profile 7.5 mm (about 0.06 $\lambda$ and $\lambda$ equals to the wavelength at center frequency) was fabricated and measured. The experiment results show that the antenna element achieves 43 $\%$ bandwidth ($\vert { S_{11}}\vert$ $< $ $-$ 10 dB) from 2.0 to 3.1 GHz. The polarization isolation between those two ports is larger than 25 dB. The element was then extended to an eight-element phased array. The measured results demonstrate that the array can scan $\;\pm\text{50}^{\circ }$ for either polarization from 2.0 to 2.6 GHz. [ABSTRACT FROM AUTHOR]

A metasurface (MTS) can be characterized in terms of dispersion properties of guided waves and surface waves. By engineering the rich dispersion relations, setting particular boundary conditions, and selecting proper excitation schemes, multiple adjacent resonance modes can be excited to realize the wideband operation of low-profile MTS antennas. We introduce the operating principles of typical dispersion-engineered MTS antennas, and review the recent progress in dispersion-engineered MTS antenna technology. The miniaturization, circular polarization, beam-scanning, and other functionalities of MTS antennas are discussed. The recent development of MTS antennas has not only provided promising solutions to the wideband and low-profile antenna design but also proven great potential of MTS in developing innovative antenna technologies. [ABSTRACT FROM AUTHOR]

In this paper, a low-profile wideband circularly polarized (CP) multiple-input multiple-output (MIMO) antenna is presented for wireless local area network (WLAN) applications. The antenna is designed with the help of two truncated corner square patches and parasitic periodic metallic plates. A prototype of the proposed antenna is fabricated and measured. The measurements indicate that the proposed MIMO antenna has usable bandwidth of 13.7%. By properly designing the configuration of the metallic plates, high port isolation of better than 20 dB is achieved. In addition, the diversity performance in terms of envelop correlation coefficient (ECC) is also calculated, showing satisfactory MIMO characteristics. Finally, compared to the other reported CP MIMO antennas in literature, the proposed design possesses exclusive features including low profile structure and wide operating bandwidth. [ABSTRACT FROM AUTHOR]

A wideband fish-bone-shaped endfire antenna utilizing odd-mode spoof surface plasmon polaritons (SSPPs) is proposed in this communication. Consisting of a microstrip-to-slotline converter and a differential-mode exciter, the feeding structure of this antenna can excite odd-mode signal on the SSPP structure. The fish-bone-shaped SSPP radiator can realize endfire radiation, which is equivalent to a row of small current sources. A tapering end is introduced to the SSPP radiator, realizing broader upper bandwidth. A prototype of this antenna is fabricated. Measured results exhibit that a wide impedance bandwidth of 70.3% (2.4–5.0 GHz) for $\vert \text{S}_{11}\vert < -10$ dB is obtained. Stable endfire radiation patterns and low cross polarization below −20 dB are also realized in the desired frequency band. The gain varies from 4.4 to 8.6 dBi within the whole operating band while a radiating efficiency of 90% can be observed. This antenna has a compact size of $1.36\lambda _{c} \times 0.86\lambda _{c} \times 0.012\lambda _{c}$ ($\lambda _{c}$ is the free-space wavelength at 3.7 GHz). [ABSTRACT FROM AUTHOR]

A low-profile wideband circularly polarized (CP) magnetoelectric (ME) antenna with high-gain and an end-fire radiation beam is proposed in this paper. It consists of a magnetic dipole (M-dipole) and two pairs of printed crossed strips to produce vertically and horizontally polarized E-field components, respectively. With the appropriate combination, the proposed ME antenna exhibits an inherent 90°-phase difference at endfire for these two field components. CP end-fire radiation, therefore, can be achieved. Two techniques using the L-probe coupled feeding structure to excite the M-dipole operating at both the basic ($0.5\lambda $ -) and higher ($1.5\lambda $ -) modes for the dual-mode resonances and using two pairs of printed strips with different dimensions for the dual-frequency resonances are introduced to realize the wideband operation. The measurement results show that the wide impedance bandwidth (IMBW) of 2.40–4.24 GHz (1.84 GHz, 55.4%) and 3 dB axial-ratio bandwidth (ARBW) of 2.36–3.86 GHz (1.5 GHz, 48.2%) are achieved. In addition, the stable end-fire radiation patterns with a peak gain of 7.57 dBi are observed over the operating band. The bandwidth for 3 dB gain variation is 2.34–3.97 GHz. Hence, the proposed antenna with its main beam in parallel with the substrate shows the potential for some point-to-point communications such as the radio-frequency identification (RFID) system. [ABSTRACT FROM AUTHOR]

A novel end‐fire circularly polarized (CP) antenna is presented by integrating a vertically polarized magnetic Yagi array, a horizontally polarized electric Yagi array, various lengths of the directors and common driven elements. Slots with nine Jesus crosses are etched on the common driven elements to extend the impedance matching bandwidth of magnetic Yagi array, while various length of directors are employed to obtain wide axial ratio (AR) bandwidth. The designed CP antenna is both numerically and experimentally validated, and experimental results agree well with electromagnetic simulated results. The fractional impedance bandwidth for ∣S11∣ < 10 dB is up to 20.7%, and AR bandwidth of less than 3 dB is up to 16.0% in fraction. [ABSTRACT FROM AUTHOR]

A novel filtering method based on the metasurface antenna (MSA) with radiation nulls is proposed without loading extra circuits. Due to the specific multiunit structure of MSA, the filtering method is first realized on each radiating metasurface (MS) unit by introducing a multifolded U-shaped slot and a defected ground structure to generate lower edge radiation nulls. Meanwhile, coplanar parasitic patches are loaded around the MS units to provide upper edge nulls and simultaneously introduce extra in-band resonances for wide passband. Thus, a low-profile, wideband, and high-gain filtering antenna is readily constructed. To verify the concept, a prototype with a low profile of only $0.04\lambda _{{0}}$ is designed and fabricated. The simulated and measured results agree well, demonstrating a good performance with large impedance bandwidth of about 20%, high average gain of 8 dBi, and high aperture efficiency of about 90%, together with high out-of-band suppression levels of about 20 dB. In addition, the radiation patterns are symmetric in both the E- and H-planes with cross-polarization suppressions of over 20 dB. Compared with the reported filtering antennas, the proposed filtering MSA can achieve the wideband filtering response in a low profile, as well as high gain with high aperture efficiency. [ABSTRACT FROM AUTHOR]

A low‐profile, high gain Fabry‐Perot Resonator antenna with a wide operation bandwidth (BW) is presented in this paper. The proposed design consists of an ellipse‐shaped dipole as a wideband radiating source, which is reflected by an artificial magnetic conductor ground plane to achieve low‐profile structure. The antenna gain can be significantly enhanced by the use of a half‐wavelength‐thick dielectric slab as a partial reflecting surface. Additionally, this dielectric slab also contributes to improving the radiation pattern characteristics of the proposed design, especially in the high frequency region. A final prototype with an overall size of 1.2λL × 1.2λL × 0.4λL (λL is free‐space wavelength at the lowest frequency of 3‐dB gain BW) has been fabricated to validate the concept. The measured results show that the proposed antenna yielded a wide 3‐dB gain BW of approximately 50.3% with a peak gain of 14 dBi and impedance matching BW of 48.9%. [ABSTRACT FROM AUTHOR]

A low-profile wideband aperture-fed microstrip patch antenna (MPA) under radiation of TM12 and TM30 modes is proposed with improved radiation patterns. Initially, the radiation characteristic of a rectangular MPA operating in TM30 mode is theoretically investigated. The results demonstrate that its E-plane sidelobe could be gradually reduced by decreasing the resonant frequency of TM30 mode (${f} _{30}$). As such, a pair of parallel slots is etched out on the radiating patch so as to significantly decrease the ${f} _{30}$. After that, the MPA under an operation of TM12 mode is further studied. It illustrates that its radiation pattern has the maximum off broadside direction and can be transformed into the broadside radiation by enlarging the length of the parallel slots. In addition, the width of the radiating patch is progressively enlarged in order to reallocate the dual modes in proximity to each other. With these arrangements, a wide bandwidth with improved radiation characteristics is obtained for the antenna under dual resonance. Finally, a prototype aperture-coupled MPA is fabricated and measured. The simulated and measured results agree well with each other, thus demonstrating that its impedance bandwidth is dramatically extended to about 14.8% with a low-profile property of about 0.048 free-space wavelength in thickness. Besides, the antenna has achieved a stable gain varied from 7.0 to 9.9 dBi over the operating band. In particular, the E-plane sidelobe level of the proposed antenna has been successfully suppressed. [ABSTRACT FROM AUTHOR]

This communication proposes a compact, wideband, two-port substrate-integrated waveguide (SIW) antenna with a central, double-slotted metallic plate flanked by two paired corrugations for radar applications. The proposed antenna uses a two-layer structure, with a slotted metallic plate with corrugations on the top layer and an FR-4 substrate SIW on the bottom layer. The antenna has compact dimensions of 63 mm $\times$ 54 mm ($2.32\lambda _{0} {\times}\,\, 1.99\lambda _{0}$) with a low profile of 7 mm ($0.26\lambda _{0}$). To understand the operating principle of the two-port SIW antenna clearly, modal analysis is performed for single-port SIW antenna. The antenna satisfies a −10 dB reflection coefficient from 10.15 to 11.58 GHz. Although the separation between the two central slots is minimized to 4 mm ($0.14\lambda _{0}$), the isolation performance remains excellent (less than −30 dB). The gain enhancement, with a narrow beam pattern for radar applications, is realized using constructive superposition of in-phase electromagnetic energy from the two slots. In addition, because the antenna has two ports, it also has a beam scanning function from −12° to +12° in its boresight direction. The experimental and simulated results from the proposed antenna are in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, a novel wideband and low-profile discrete dielectric lens (DDL) antenna is presented. The proposed unit cells of DDL with the square-pyramid structure can realize wideband antireflection at an air–dielectric interface. By increasing the phase compensation range, the DDL antenna with very large gain bandwidth but large DDL thickness would be achieved. Furthermore, based on the large gain bandwidth technology, a novel multifolded lens structure is proposed to realize the low-profile design, in which a broadband polarization rotation reflection surface is proposed, while a polarized grid is used appropriately. Finally, the proposed multifolded DDL antenna can achieve a very large gain bandwidth, while the thicknesses of the DDL unit cell and the total antenna can be greatly reduced. For demonstration, the proposed multifolded DDL antenna is fabricated and measured. The fabrication was implemented by using a simple and low-cost 3-D printing technology. The results show that the proposed lens antenna can realize a 1 dB gain drop bandwidth of 43%, thickness of less than 1/3 focal-length-to-diameter ratio, and maximum aperture efficiency of 32%. Good agreement can be observed between the measurement and simulation. [ABSTRACT FROM AUTHOR]

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 $3 \times 3$ 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. [ABSTRACT FROM AUTHOR]

A low profile shorted-patch antenna (SPA) with enhanced bandwidth and reduced the H-plane cross-polarization (cross-pol) is proposed in this communication. Initially, the radiated field of a conventional SPA is theoretically investigated. It is demonstrated that its high cross-pol of the H-plane radiation patterns can be reduced by introducing a pair of shorting walls underneath the nonradiating edges of the SPA. Then, the width of the radiating patch is progressively enlarged so as to decrease the resonant frequency of TM1/2,2 mode. After that, an array of six shorting pins is loaded underneath the patch radiator toward pushing up the resonant frequency of TM1/2,0 mode. In addition, the linear Slots 1 and 2 are cut on the rectangular patch to reduce the resonant frequency of TM3/2,0 mode and achieve a good impedance matching, respectively. With these arrangements, all of these three radiative modes are reallocated in proximity to each other, leading to the formulation of the improved SPA with low profile, wide-bandwidth, and low cross-pol performances. Finally, the proposed antenna is fabricated and measured. The measured results show that its impedance bandwidth is extended up to about 26.2% under triple-mode resonance. In addition, its thickness is maintained as small as about 0.059 free-space wavelength. In particular, the H-plane cross-pol of the SPA is successfully decreased to below −12.3 dB over the operating band. [ABSTRACT FROM AUTHOR]

This paper presents a log-periodic monopole array (LPMA) with uniform spacing and uniform height operating in a wideband of 2–6 GHz. Different from the conventional LPMA with logarithmic spacing and height, the proposed antenna with uniform spacing and uniform height simplifies the design procedure and retains a low profile. The top-hat monopoles and folded top-hat monopoles are used to reduce the height of the antenna. A maximum bandwidth of 3:1 is theoretically proposed by considering the maximum and minimum spacing factor of the array. A meandering microstrip line is employed as the feeding line. The compensation of the length of the feeding line is proposed for the uniformly spaced LPMA compared to the conventional array. A prototype is fabricated and tested. Measured results indicate that an impedance bandwidth from 2 to 6 GHz (3:1) with VSWR < 2 is achieved. The measured peak realized gain is in the range of 6.6–8.7 dBi, which has great potential in many communication systems such as missile and airborne applications. [ABSTRACT FROM AUTHOR]

A series of E-band low-profile wideband antenna arrays with 45° and ±45° dual linear polarizations is presented for high-speed millimeter-wave communication applications. The array element consists of a corner-fed patch with a tilted slot cut at its edge, which suppresses unwanted modes in order to generate the desired 45° linear polarization. Comparing to a traditional 45° tilted patch, the proposed element gets rid of the bending feedline and realizes a higher isolation level between adjacent patches in the side-by-side arrangement. For proof-of-concept demonstration, a $2 \times 8$ array with 45° linear polarization was fabricated and measured, exhibiting a good agreement between simulation and measured results. The proposed array prototype possesses a −10 dB impedance bandwidth of 10.6% (74.3–82.5 GHz). Moreover, a dual $1 \times 8$ array with ±45° dual polarization is also presented, showing a bandwidth of 9.7% (74.4–81.9 GHz) and a high isolation level of greater than 25 dB. The proposed E-band planar arrays own the advantages of low profile, i.e., $\sim 0.067\lambda _{0}$ , single layer, low fabrication cost, simple structure, wide operational bandwidth, i.e., ~10%, and polarization flexibility. They represent promising candidates for high-speed E-band communications. [ABSTRACT FROM AUTHOR]

A low-profile, wideband, high-gain reconfigurable antenna, which is capable of switching among four linear polarizations (LPs) at every 45° rotation, namely, 0°, 45°, 90°, and 135° LP, is presented. The proposed structure is based on two half-ellipse-shaped dipoles arranged perpendicularly and is center fed by coaxial cable. The antenna polarization can be switched by selecting the appropriate dipole arms to be excited as well as controlling their phases using p-i-n diodes. To achieve low-profile, high-gain, and unidirectional radiation patterns in a wide range of frequency, a combination of an artificial magnetic conductor and a shallow pyramid-shaped cavity is also utilized in this design. An optimized prototype with low profile of $0.1\lambda $ at the lowest operating frequency yields a measured overlapped impedance bandwidth (BW) of 53.9% for all polarization states. In addition, a radiation efficiency of greater than 78% and measured broadside gain from 6.8 to 10.9 dBi are observed over the entire operation BW. [ABSTRACT FROM AUTHOR]