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A compact dual-band circularly polarized (CP) shared-aperture antenna is proposed for satellite communication. The antenna enables simultaneous dual-band functionality and CP radiation with right-handed CP in the Ku band and left-handed CP (LHCP) in the Ka band. The shared-aperture is implemented by integrating two independent subapertures, which function through frequency-multiplexed, resulting in a minimized profile (0.04 $ {\lambda _0} $ λ 0 ) and reduced complexity, making it an ideal choice for array applications. To enhance inter-frequency isolation, a circular arrangement of metal vias is incorporated. The measured results indicate that the antenna effectively encompasses a 3 dB axial ratio (AR) bandwidth of 15.6–16.5 GHz in Ku and 26.5–27.5 GHz in Ka bands. Additionally, it exhibits a broader 10 dB impedance bandwidth (IBW) and superior port isolation bandwidth exceeding 30 dB. [ABSTRACT FROM AUTHOR]

Communication systems need antennas with wide bandwidths to provide large throughput, while imaging radars benefit from high gain for increased range and wide bandwidths for high-resolution imaging. This paper presents the design and evaluation of a wideband, high-gain antenna that achieves an average gain of 9.7 dBi over a bandwidth of 1.49 GHz to 3.92 GHz by using multiple in-phase radiating apertures. The antenna has a unique structure with a central rectangular short-circuited patch sandwiched between two back-to-back U-shaped radiating patches and two flanking H-shaped short-circuited patches. Each of the U-shaped patches employs a coplanar waveguide as feeding to achieve ultra-wideband impedance matching. Benefiting from design arrangement, in-phase electrical field distributions appear at the gaps between the patches that result in equivalent radiating magnetic currents in the same direction. Theory analysis shows that the close-spaced, same-direction magnetic currents created by the radiating apertures intensify the radiation and increase antenna gain within its impedance bandwidth. Simulated data show that the use of the coplanar waveguide feeding and short-circuited patches increase the bandwidth from 65 MHz to 2.43 GHz. Moreover, the short-circuited patches increase the gain by 3.45 dB at 2.4 GHz. Simulation and measurement results validate the design and show that the antenna features a maximum gain of 11.3 dBi and an average gain of 9.7 dBi in a fractional bandwidth of 89.8%. Because of the high gain values and the wide bandwidth, the antenna is particularly suited for long-range communication systems and high-resolution radar applications. [ABSTRACT FROM AUTHOR]

A novel aperture‐shared dual‐wideband 5G antenna with dual polarization in the sub‐6 GHz band and multi‐input multi‐output (MIMO) function in the 28‐GHz band is presented in this work. A dual‐polarized megnetoelectric dipole (ME‐dipole) with wide bandwidth is introduced in the sub‐6 GHz band. Based on the partial structure reuse method, four 2 × 2 substrate integrated waveguide (SIW) cavity‐backed patch arrays are integrated into the electric dipole structure of the ME‐dipole to construct a 28‐GHz 2 × 2 MIMO system. Two high‐order SIW cavity modes that cooperate with patch modes are used to enhance bandwidth in the 28‐GHz band. For demonstration, a prototype of the proposed antenna was fabricated and measured. The simulated results are in good agreement with the measured results, showing wide bandwidths of 39.6% and 10.85% in the sub‐6 GHz and the 28‐GHz bands, respectively. In addition, excellent measured in‐band and cross‐band isolations of over 44.4 dB and 45.2 dB are obtained, respectively. [ABSTRACT FROM AUTHOR]

A wideband and circularly polarized hybrid ring CDRA is proposed for the applications of C, X and Ku-band. A small size two-headed drum-shaped aperture (Damaru shaped) inclined at 45° and microstrip line feed generates two orthogonal modes (HEMx11δ and HEMy11δ). The suggested ring CDRA of wideband characteristic is resonating between frequency band 6.96 to 14.12 GHz with 67.93% (7160 MHz) impedance bandwidth. oreover, dual-band circular polarization characteristics are also achieved from 8.22 to 9.53 GHz and 12.29 to 13.71 GHz with 3-dB axial ratio bandwidth (ARBW) of 14.76% (1310 MHz) and 10.92% (1420 MHz) respectively. The impact of various parameters of ring CDRA and aperture orientation on the functionality of the suggested antenna is also studied. The proposed radiator is fabricated on a 40 × 40 mm2 (0.93 × 0.93λ02 at lower cut-off frequency 6.96 GHz) FR-4 substrate of 1.6 mm thickness. Moreover, peak gain of 7.43 dB at frequency 12.66 GHz and radiation efficiency greater than 80% in the whole operating frequency is also achieved. [ABSTRACT FROM AUTHOR]

We designed a mesoscopic dielectric cuboid antenna connected to a flangeless WR-3.4 open-ended waveguide, and the antenna characteristics at 300 GHz were examined through simulations and experiments. Simulations confirmed that the flangeless design eliminated the flange-induced ripples in the radiation pattern, whose shape varied with frequency, and that the antenna operated in the full bandwidth of the WR-3.4 waveguide (220–330 GHz). Prototypes were then fabricated based on the simulation findings. A prototype with an antenna aperture area of 1.5 mm × 1.5 mm and an antenna length of 2.35 mm exhibited an antenna gain of 17.2 dBi at 300 GHz and a voltage standing wave ratio of less than 1.5 throughout the WR-3.4 waveguide bandwidth. The level of the side lobes at about ± 30 degrees in the E-plane pattern was approximately - 10 dB that of the main lobe. Therefore, the proposed antenna, connected to a flangeless waveguide, is a promising antenna for use in future short-range high-speed terahertz wireless applications such as kiosk downloads and board-to-board communication. [ABSTRACT FROM AUTHOR]

Based on the Pancharatnam-Berry phase principle, a wideband low-profile transmissive metasurface was designed and applied to a transmitarray antenna (TA). While a full transmission phase range of 360° was achieved by rotating the proposed unit cell, the transmission coefficient was always close to 1 in the frequency range of 10.4–11.6 GHz. Hence, a TA comprised of 20 × 20 unit cells of size 180 mm × 180 mm was designed and fabricated. The simulated results agreed well with the experimental data, validating the excellent performance of the proposed metasurface structure. The measured peak gain of the TA was 21.64 dB at 11 GHz, resulting in an aperture efficiency of 34%. In addition, we attained a 12% 1-dB gain bandwidth (10.2–11.5 GHz) and an 18% 3-dB axial ratio bandwidth (10–12 GHz) for the TA. The proposed metasurface exhibits distinct performance benefits in terms of having wide bandwidth, low-profile, and high-efficiency, as well as represents a promising design option for a high-performance TA. [ABSTRACT FROM AUTHOR]

A single-layer multimode metasurface antenna is proposed with a coplanar waveguide (CPW)-fed aperture. The ultra-wideband (UWB) performance is implemented based on a three-step evolution process with the aid of characteristic mode analysis (CMA). Considering the efficient excitation with a fixed feeding structure, the metasurface modal current variation at different frequencies is analyzed and optimized, in addition to that at the resonant frequency. Correspondingly, the metasurface is firstly designed utilizing an array of 4 × 4 patches. Then, the 1 × 3 and the 1 × 1 parasitic patch arrays are located near the edge patches. Finally, every patch is split into two by a center slot along the current distribution of the required polarization. Four resonant modes of the metasurface become more desirable step by step and can be efficiently excited over the entire band. To enhance the impedance matching level, a pair of 5-stage gradient transitions are added to the CPW-fed slot. The slot mode combined with the four modes further improves the bandwidth. The experimental results demonstrate that the proposed antenna exhibits a 3 dB gain bandwidth of over 74% (4.0–8.7 GHz) with a peak gain of 8.2 dBi. The overall dimensions of the prototype are 1.40λ0 × 1.40λ0 × 0.075λ0 (λ0 is the free-space wavelength at 6 GHz). [ABSTRACT FROM AUTHOR]

Simultaneously enhancing multiple antenna performance parameters is a demanding task, especially with a challenging set of design goals. In this paper, by carefully deriving a compatible set of enhancement techniques, we propose a compact/lightweight/low-cost high-performance L-band octagonal cavity-backed hybrid antenna with multiple attractive features: dual-polarization, wide impedance bandwidth, low cross-polarization, high gain, and high aperture efficiency. The ground cavity is octagonal, which allows the antenna to have a small footprint, and, more importantly, low cross-polarization and high aperture efficiencies when compared to a commonly-used square design. The hybrid design relies on the resonance merging of two radiating elements, i.e., radiating feedlines and a conductive open prism, to form a wide impedance bandwidth. To permit polarization diversity and low cross-polarization, it is differentially and orthogonally fed. Herein, a series of parametric simulation studies on antenna configurations provide information on how to improve the impedance bandwidth and cross-polarization performance. To verify the simulation studies, an antenna prototype was fabricated and tested. Excellent agreement between the simulated and measured results was reached. [ABSTRACT FROM AUTHOR]

Broadband and the high gain circularly polarised antenna are designed in a single-layered planar substrate. An array of 3 × 3 truncated corner square patches are designed as a metasurface antenna on one side of the substrate and the metasurface antenna is fed by a stub-loaded uniform aperture CPW feed on another side of the substrate. In the metasurface antenna, the size of the central patch is increased for improving the bandwidth of impedance bandwidth and 3 dB axial ratio. Furthermore, the amount of truncation is reduced in the patches surrounding the central patch to enhance the bandwidth of impedance bandwidth and 3 dB axial ratio bandwidth. The designed metasurface antenna has achieved an impedance bandwidth of 38.2% (4.5–6.63 GHz) with an axial ratio bandwidth of 13% (5.0–5.7 GHz). Moreover, the antenna has a peak gain of 10.36dBic. The simulation and measurement results are compared. [ABSTRACT FROM AUTHOR]

A novel circularly polarized (CP) planar aperture antenna that is completely self‐designed and manufactured with high gain and wideband is proposed in this paper. The antenna adopts a differential feed network so that the energy is evenly transmitted to the radiation patch. By surface current analysis, the closed loop with linearly polarized (LP) characteristics is changed into two arms of different lengths to generate CP radiation. The uniformity and symmetry of energy improve the wideband and high‐gain performance of the antenna. The fabricated antenna prototype has the characteristics of a wideband of 33.3% (28.1–39.3 GHz) and an average gain of 11.4 dBic, which could achieve 3‐dB axial ratio bandwidth of 12.4% (35.2–39.6 GHz) and a stable left‐handed CP and radiation patterns throughout the operating bandwidth with a peak gain of 15.8 dBic. [ABSTRACT FROM AUTHOR]

In this work, a high-gain and wideband microstrip-fed slot antenna is proposed and investigated, which is composed of an anisotropic metasurface (AMS) and an aperture coupled structure. The proposed microstrip antenna with four resonances can be obtained by merging the AMS with an anomalous inverted π-slot feed structure in a low profile (1.07λ x 1.07λ x 0.06λ). The simulated results indicate that the proposed microstrip antenna can achieve a wide impedance bandwidth of 56.1% from 3.32 to 5.91 GHz, which is verified by experiment. In addition, the measured results show that the peak gain of the proposed microstrip-fed slot antenna is 10.7 dBi at 5.3 GHz, and the relative bandwidth of 3-dBi gain is 42.2% from 3.85 to 5.91 GHz. Compared with previous works, the proposed design has a lower profile while achieving a much wider operating bandwidth, where the four controllable resonance modes offer more possibilities for band expansion. This work shows potential application in integration with high data rate systems. [ABSTRACT FROM AUTHOR]

A novel S/Ka dual-band dual-circularly polarized (CP) shared-aperture antenna is proposed in this paper. In the Ka-band, the reflectarray adopts two distinct CP elements, both of which achieve 360° phase shift and linear phase response in the wideband. In the S-band, the radiation array adopts a 4 × 4 units cut-corner square patch to achieve CP performance. Additionally, a steerable beam is achieved through a phase shift feeding network. To effectively improve the antenna aperture utilization and efficiency, the S-band radiator is reused as a part of the Ka-band reflecting ground to realize the aperture-sharing. Experimental results demonstrate that the S-band operating bandwidth covers 2.35–2.7 GHz, achieving a peak gain of 18.6 dBic and an aperture efficiency of 89.2 %. Furthermore, the S-band enables ± 30° beam steering. In the Ka-band, the operating bandwidth covers 28–32 GHz, with a measured 2-dB axial ratio bandwidth is 10.3 %, a peak gain of 37.5 dBic, and an aperture efficiency of 48.1 %. Therefore, a dual-band dual-CP shared-aperture antenna with high aperture efficiency is realized. The antenna offers beam steering in the S-band and wideband capabilities in the Ka-band, making it a valuable candidate for satellite communication systems. [ABSTRACT FROM AUTHOR]

A low-profile (LP) metasurface antenna is proposed for broadband circularly polarized (CP) operations. The metasurface radiator, formed by a 5 × 5 array of square patches, has a microstrip line fed at its bottom through a shorted annular-ring slot centered on the ground plane. First, the characteristic mode analysis (CMA) methodology is employed to examine the intrinsic modes of the metasurface. Subsequently, a pair of mutually orthogonal modes is selected and excited by the feeding structure with a 90° phase difference to produce CP radiation. For the purpose of verification, a prototype antenna is developed, and the obtained data reveal that the antenna exhibits an impedance bandwidth of 43.9% ranging from 4.8 to 7.5 GHz (S11<−10 dB). The 3-dB axial ratio bandwidth is 22.2% in the range of 5.6–7 GHz, among which a satisfactory left-handed CP radiation is achieved, and the maximum gain in the broadside direction reaches 9.3 dBic at 6.9 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a method was developed to achieve the instantaneous bandwidth enhancement of a variable inclination continuous transverse stub (VICTS) antenna. The aperture of the VICTS antenna was divided into a subarray, and the true-time delay was introduced to reduce the dispersion of the antenna. The method has low loss and is suitable for the entire beam scanning range. To demonstrate this method, a proposed VICTS antenna composed of 2 × 2 subarrays was designed and simulated. Compared with the traditional VICTS antenna of the same aperture size, the gain loss was reduced by at least 52% and the 3/4-dB gain-loss bandwidth increased from 2.5% to 4.2%. The impedance bandwidth of 16.7% with the S 11 value of each subarray below −15 dB was achieved, and the sidelobe of the whole antenna was below −10 dB. The antenna radius was 0.34 m, and the aperture efficiency was 14.8%. The proposed antenna is a suitable candidate as a gateway station antenna for low earth orbit (LEO) satellite communication. [ABSTRACT FROM AUTHOR]

In this article, corrugated conductor plates with slow wave properties are used as slow wave unit cell structures to increase the aperture efficiency of the transmitarray antenna. The slow wave structure is composed of a simple conductive plate and a corrugated conductor plate facing each other. Two types of unit cells are considered for the design of the transmitarray antenna. In the first type, the spacing and height of the corrugated sections are constant, and only by changing the number of the corrugation the phase shift is created. In the second type, the distance of the corrugated sections and the number of the corrugation is constant, and only by varying the corrugated height, the phase shift is controlled. These slow wave structures can easily cover 360° and are also suitable for large transmitarray. An array of such two types of slow wave unit cell structure is placed in front of the horn antenna and the aperture efficiency of the antenna is improved by the required phase correction. The transmitarray antenna based on the second type of the unit cell is fabricated and measurement results indicate that the transmitarray antenna has a maximum aperture efficiency of 89.4% at the frequency of 10.5 GHz and 1‐dB gain bandwidth of 30%. [ABSTRACT FROM AUTHOR]

A one‐dimensional (1‐D) ultra‐wideband conformal connected slot array with reduced scattering characteristics is presented. The proposed array accomplishes a practical design completely conformal to a wing platform by closely attaching the antenna aperture to the curved surface. A conformal metamaterial absorber (CMA) structure is employed to control the out‐of‐band scattering, and the resistive patches are analyzed for the reduction of radiation loss. Additionally, a parasitic metal block is introduced for the improvement of VSWRs in the low‐frequency band. The designed 1‐D infinite array is able to achieve 4:1 impedance bandwidth from 0.5 to 2.0 GHz with an active VSWR <3.0 for scanning up to ±45°. In comparison with the reference array, a significant monostatic scattering reduction is achieved from 6.0 to 18.0 GHz with the radiation performances well preserved. The overall thickness of the conformal array is only about 0.31λh at the highest operating frequency. A 2 × 8 conformal array prototype is fabricated and measured. Measured results are in good agreement with simulated ones, thus demonstrating effectiveness. [ABSTRACT FROM AUTHOR]

In this article, a low‐profile wideband metasurface‐loaded patch antenna is proposed. The antenna utilizes a compact structure of square ring type metasurface loaded patch to increase the bandwidth of traditional microstrip patch antenna. By introducing a patch‐induced metasurface mode at higher frequency combined with the fundamental patch mode at lower frequency in the band of interest, a dual‐mode operation is revealed with the aid of characteristic mode analysis. Compared with conventional metasurface antenna fed by a long radiating slot, the proposed antenna can achieve a 30% reduction in aperture size with a simpler configuration, clear dual‐mode operation and significant improvement of backward radiation. To validate the concept, a 1 × 4 array prototype of proposed antenna is manufactured under a low profile of 0.04λ0 (λ0 is the free space wavelength at 27.5 GHz). The measured results indicate the antenna array achieves a wide impedance bandwidth of 22.8% with a peak realized gain of 13.1 dBi and a high front‐to‐back ratio over 20 dB. [ABSTRACT FROM AUTHOR]

A broadband dual‐polarized filtering antenna with a compact size and high skirt selectivity for fifth‐generation (5G) sub‐6 GHz applications is proposed in this paper. The antenna is composed of two feeding networks and four shorted patches, which is based on a slot‐aperture excitation scheme. By employing the novel defected ground LC resonator structures (DGLCRSs) and two different types of open‐ended structures, the proposed dual‐polarized antenna realizes satisfactory filtering performance as well as an improved operating bandwidth simultaneously. During which, four radiation nulls are generated at the both band edges and can be individually controlled. To further enhance the upper stopband performance, four pairs of meander‐shaped slots are inserted on the patches symmetrically, which introduces another controllable radiation null. The working mechanism for achieving the filtering responses is provided. A fabricated prototype and experimental results demonstrate that an impedance bandwidth of 42.9% (3.3–5.1 GHz) is first obtained in a low‐profile dual‐polarization structure, covering the entire 5G N77/N78/N79 bands. The measured gain is about 8.1 dBi within the passband, while the stopband suppression is better than 16 dB up to 1.85 fc. These merits make the proposed antenna quite potential for the 5G new radio communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a fractal inspired metamaterial superstrate is proposed for the gain enhancement of microstrip patch antenna resonating at 2.4 GHz. Fractal structure is used as the metamaterial unit cell, which is designed on a FR4 substrate with a thickness of 1.6 mm. The metamaterial unit cell exhibits near-zero refractive index at 2.4 GHz. The superstrate consists of a 2×2 array of metamaterial unit cells which acts as a partial reflective surface of Fabry-Perot (FP) cavity. The distance between the antenna and the superstrate is optimized by the FP resonance condition. The antenna has a directional radiation pattern more than the microstrip patch antenna. The antenna gives a peak gain of 7 dBi with a gain enhancement of 4 dB and a beamwidth reduction of 23° and 2° along H plane and E plane respectively. The aperture efficiency of the antenna is 80.47%. The whole structure is simulated and analyzed using finite element method. The simulated and the measured results show good agreement. [ABSTRACT FROM AUTHOR]

The gain of some aperture antennas can be significantly increased by making the antenna near-field phase distribution more uniform, using a phase-transformation structure. A novel dielectric-free phase transforming structure (DF-PTS) is presented in this paper for this purpose, and its ability to correct the aperture phase distribution of a resonant cavity antenna (RCA) over a much wider bandwidth is demonstrated. As opposed to printed multilayered metasurfaces, all the cells in crucial locations of the DF-PTS have a phase response that tracks the phase error of the RCA over a large bandwidth, and in addition have wideband transmission characteristics, resulting in a wideband antenna system. The new DF-PTS, made of three thin metal sheets each containing modified-eight-arm-asterisk-shaped slots, is significantly stronger than the previous DF-PTS, which requires thin and long metal interconnects between metal patches. The third advantage of the new DF-PTS is, all phase transformation cells in it are highly transparent, each with a transmission magnitude greater than − 1 dB at the design frequency, ensuring excellent phase correction with minimal effect on aperture amplitude distribution. With the DF-PTS, RCA gain increases to 20.1 dBi, which is significantly greater than its 10.7 dBi gain without the DF-PTS. The measured 10-dB return loss bandwidth and the 3-dB gain bandwidth of the RCA with DF-PTS are 46% and 12%, respectively. [ABSTRACT FROM AUTHOR]

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Radial line slot array (RLSA) antennas have attractive features, such as high gain, high efficiency, and planar low profile, but their gain–bandwidths have been limited to less than 10%. This article presents a method to significantly increase the gain–bandwidth of RLSAs to over 30%. The key to the method is the application of a nonuniform radial TEM waveguide as opposed to the radially uniform TEM waveguide used in conventional RLSAs. Hence, the condition for maximum radiation is satisfied at a wide range of frequencies by different sections of the RLSA. To demonstrate the concept, several circularly polarized RLSA designs and one prototype are presented. The measured results of the prototype demonstrate an unprecedented 3 dB gain–bandwidth of 27.6%, a peak gain of 27.3 dBic, 3 dB axial ratio bandwidth greater than 31.1%, and a 10 dB return loss bandwidth greater than 34.8%. The overall measured bandwidth of the RLSA in which gain variation and axial ratio are within 3 dB and return loss is greater than 10 dB is from 9.7 to 12.8 GHz or 27.6%. Its extremely high measured gain–bandwidth product per unit area (GBP/A) of 88 indicates excellent overall performance in terms of bandwidth, gain, and area. [ABSTRACT FROM AUTHOR]

A method for expanding the bandwidth of slot and patch antennas is proposed in this article. The use of grid‐slotted patch helps to improve the impedance matching of the antenna, thus the bandwidth can be extended. The design process and an analysis of using a grid of slots to increase the bandwidth of a slot antenna is first given. The simulated S11 of the broadband slot antenna is less than −11 dB in the range of 2.6 to 3.42 GHz. To further demonstrate the method, an aperture‐coupled patch antenna with grid‐slotted patch is designed. The measured S11 of the broadband patch antenna is less than −10 dB in the range of 1.95 to 4.15 GHz and the peak gain is 9.6 dBi. [ABSTRACT FROM AUTHOR]

A novel resonant cavity antenna (RCA) with low sidelobe levels over an enhanced bandwidth is presented. Radiation bandwidth of the antenna is increased by using a pair of complementary FSS layers, giving a positive reflection phase over a wide frequency range, as the proposed PRS. Low sidelobes are achieved by lowering the reflection amplitude of the PRS along its length while keeping reflection phase almost the same throughout the operating band. The performance of the proposed PRS is validated by creating a circular aperture RCA and measuring its radiation characteristics. The cavity is excited by an aperture coupled patch antenna having a broad impedance bandwidth. Prototype RCA gives a peak realized gain of 16.1 dBi and a 3-dB gain bandwidth of 8.6% ranging from 14.5 to 15.8 GHz. Measured sidelobe levels are reduced, respectively, to less than −17 dB and −23 dB in the E- and H-plane of the prototype antenna. [ABSTRACT FROM AUTHOR]

This article proposes a novel patch antenna using a polarization control module to achieve a broad matching bandwidth and broad 3‐dB gain bandwidth over the entire axial ratio (AR) range. The proposed antenna consists of a shorted radiating patch, an L‐shaped indirect feed, and a polarization control module that can adjust AR properties over the entire AR range (−1 < AR < 1) with a broad 3‐dB gain bandwidth for use in various practical applications. The measured results demonstrate that the proposed antenna can adjust the polarization properties with a broadband matching bandwidth of more than 27% (370 MHz) and a broad 3‐dB gain bandwidth greater than 26% (351 MHz) over the entire AR range. [ABSTRACT FROM AUTHOR]

A slit-loaded series feed network and its design procedure were proposed for millimeter-wave (mm-wave) array antennas with a low sidelobe level (SLL) over a wide bandwidth. In the proposed feed network, slit structures are used to suppress internal reflections within the array and to control the aperture amplitude in such a way to reduce the SLL. Four types of slit-loaded structure units are investigated to control the coupled power on an antenna element. A $1 {\times }13$ end-fed and $2 {\times }26$ center-fed array antennas were designed and fabricated based on the proposed design procedure, and their performances were measured. The proposed arrays were shown to have impedance bandwidths of 11.3% (75–84 GHz) and 10.2% (77.5–85.8 GHz), respectively. Moreover, they show stable radiation patterns with low SLLs under −17 dB over the frequencies of 75–83 and 78–84 GHz, respectively. The designed arrays were compared with other mm-wave array antennas and shown to have a lower SLL over wide bandwidths. [ABSTRACT FROM AUTHOR]

A wideband high-efficiency millimeter-wave (mm-wave) circularly polarized (CP) array which is constituted by novel planar substrate integrated waveguide (SIW)-fed S-dipoles is presented in this communication. The proposed mm-wave CP S-dipole consists of two rotational symmetric curved arms and is fed differentially through aperture coupling, which features simple configuration and excellent performance. Detailed analysis is given to explain the operating principles of this element. It is noted that superior element performance including a wide impedance bandwidth of 43%, a wide 3 dB axial ratio (AR) bandwidth of 36%, and 1 dB gain bandwidth of 38% is achieved by the planar SIW-fed S-dipole. By feeding 64 in-phase S-dipole elements through a full-corporate SIW feeding network, a planar wideband highly efficient mm-wave $8 \times 8$ CP array is realized. To verify the design concept, a prototype operating at Ka-band is fabricated and measured. The measurement results indicate that the proposed array achieves a wide overlapped bandwidth of 27.6%, a high antenna gain of 25.2 dBic, and a high aperture efficiency of 89.9%. Attributed to the planar and robust array structure as well as its excellent performance, the presented array is a good candidate for various mm-wave applications. [ABSTRACT FROM AUTHOR]

Vertical microcavity surface-emitting lasers employing quantum wells and small aperture buried-oxide current and field confinement are demonstrated with wider mode spacing and faster spontaneous carrier recombination (enhanced Purcell factor), lower threshold current, larger side mode suppression ratio (SMSR), and higher photon density and temperature insensitivity. The result is a microcavity laser that achieves higher microwave modulation bandwidth (f-3dB = 15.8 GHz) at ultra-low power consumption (1.5 mW) with a slope for the modulation current efficiency factor (MCEF) = 17.47 GHz/mA-1/2, as well as a better quality eye diagram in high-speed data transmission. The microwave behavior model for the microcavity laser is used to estimate the enhanced recombination and reduced lifetime. [ABSTRACT FROM AUTHOR]

Design of compact wideband circularly polarized (CP) antennas is challenging due to the necessity of simultaneous handling of several characteristics [reflection, axial ratio (AR), and gain] while maintaining a small size of the structure. Antenna redesign for various operating bands is clearly more difficult yet practically important because intentional reduction of the bandwidth (e.g., by moving the lower edge of the operating band up in frequency) may lead to a considerable size reduction, which can be beneficial for specific application areas. This article proposes a rigorous approach to rapid redesign of miniaturized CP antennas involving inverse surrogate models and fast electromagnetic (EM)-based parameter tuning. Our methodology allows for a precise control of the lower operating frequency of the CP antenna (both in terms of the impedance and AR bandwidth) and accomplishing the geometry parameter scaling at an extremely low cost of a few EM analyses of the structure at hand. Our methodology is demonstrated by redesigning a compact wide slot CP antenna in the range of 3.2–5.8 GHz. The proposed approach can be used for fast rendering of the bandwidth/size tradeoffs (the footprints obtained for the verification structure range from 783 to 482 mm2), thus determining the most suitable designs for particular applications. The numerical findings are experimentally validated. [ABSTRACT FROM AUTHOR]

A novel wideband high-gain circularly polarized (CP) antenna is proposed and investigated for the 60 GHz high-throughput communication and the 77 GHz automobile radar system. The design consists of a rectangular horn, a hyperbolic lens, and an artificial anisotropic polarizer. To minimize the thickness of the polarizer, the properties of the artificial anisotropic material (AAM) for generating CP wave are discussed analytically. Minimal polarizer thickness and the corresponding component ratio are provided mathematically. In comparison with other approaches, the proposed design achieves a relatively high-gain and wideband performance with a minimal thickness. The antenna exhibits a wide impedance bandwidth of more than 39% (VSWR < 2) from 55 to 82 GHz and a wide axial ratio (AR) bandwidth of more than 32% (AR < 3 dB) from 56 to 77 GHz. The average gain is 17 dBic. Good unidirectional radiation characteristics are achieved with low fabrication cost. In addition, the off-body lens and the polarizer could be directly migrated to other radiating sources with the concrete analytical guidance for polarizer design. [ABSTRACT FROM AUTHOR]

This paper presents a new high gain compact aperture-coupled circularly polarized antenna for WLAN applications. The proposed antenna comprises an asymmetric X-shaped slot etched on a circular patch and fed through the coupling between an annular slot and a microstrip line. The circular polarization is mainly due to the asymmetrical crossed-slots, respecting the angle of 450 between its two arms. The antenna with overall size of 60 × 60 × 5.83 mm3 has a measured 10-dB impedance bandwidth of 36%, a 3-dB axial ratio bandwidth of 3.47% (5.67-5.87 GHz) and 1-dB gain bandwidth of 19.5% (4.85-5.90 GHz) with a peak gain of 8.65 dBi. To validate the simulated results, a prototype was fabricated, and good agreement between simulations and measurements has been accomplished. [ABSTRACT FROM AUTHOR]

This study presents a novel compact circularly polarized antenna for universal ultrahigh-frequency (UHF) radio-frequency identification (RFID) handheld reader applications. The antenna is composed of a coplanar waveguide (CPW) L-shaped feedline mounted at the right edge of the square slot at the bottom of the ground plane to realize a circular polarization; a horizontal stub protruded from the right side of the square slot towards the slot centre, and a vertical stub is mounted at the lower left of the square slot. The designed antenna printed on one ground plane layer of a low-cost FR4 substrate with an overall size of 120×120×1.6 mm3. The measurement results show indicate that the fabricated antenna achieves a wide axial ratio (AR) bandwidth of 460 MHz (818–1278 MHz), wide impedance bandwidth of 54.6% (630–1103 MHz), and a measured peak gain of 4.0 dBi. The proposed antenna is a good candidate for compact universal UHF RFID handheld reader applications (840–960 MHz). [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 novel $W$ -band left-hand circular polarized (LHCP) cylindrical waveguide feed horn antenna is proposed. The proposed antenna features an inbuilt polarizer structure and a single side-fed linear polarized input to offer symmetric LHCP radiation pattern. The internal polarizer structure consists of nine pairs of circular cavities to generate a circularly polarized wave, eliminating the need for an orthomode transducer or a complex septum. The side-fed horn reduces the overall length by eliminating the rectangular to circular waveguide transition. The proposed horn antenna’s electrical dimension is $7.2\lambda \times 3.9\lambda \times 1.4\lambda $ at 84 GHz. The antenna has impedance matching ($S_{11}$ below −15 dB) and axial ratio below 1.2 dB from 79.5 to 88 GHz. The horn is used as a feed source for an offset parabolic reflector of 10 cm diameter and small $f/D$ ratio 0.25, which can fit inside a CubeSat. The reflector antenna provides the simulated right-hand circular polarization (RHCP) directivity of 36.6 dBic at 86 GHz with spillover loss of 0.83 dB. The feed reflector assembly is also simulated with the complete aluminum CubeSat chassis. The measurement of the prototyped feed horn and the offset parabolic reflector antenna validates the analysis and simulation results. [ABSTRACT FROM AUTHOR]

A 5:1 frequency bandwidth aperture array antenna based on a new planar structure is reported. Dual polarization is implemented with high cross-polarization discrimination over ±45° scan angle from zenith. It is a low-loss cost-effective approach using minimum dielectric materials. In the proposed planar antenna array design, a mutual coupled interconnected ring structure is used which extends the operational frequency band to the region where the element separation can be considerably greater than half a wavelength, unlike the previously reported interconnected array structures. Hence, the total number of elements can be reduced for a specified aperture size. The dual polarization has coincident phase centers and in the implementation reported here two low-noise amplifiers on the same board are integrated with a pair of dual-polarized elements to form an active array. A 10 by 10 element array prototype of the design has been manufactured and the measured results confirm it as a low cost, high-performance front-end solution. [ABSTRACT FROM AUTHOR]

In this paper, the combined antenna array is developed to maximize the effective potential gain ($G_{ep}$) within finite aperture area for the high-power ultra-wideband (UWB) radiation. The idea is to make the antenna element as small as possible, so that more elements can be arranged within the prescribed aperture area to maximize $G_{ep}$ of the UWB system. On the other hand, the antenna element should match the pulse excitation. This means that in the frequency domain, the working band of the antenna element should cover the spectrum of the radiated pulse, and in the time domain, critical parameters of the radiated field (e.g., rise time of the monopolar pulse) should not be distorted, and those can be the principles for the UWB antenna to match the pulsed excitation, based on which the minimum size of the antenna element can be determined. With this method, a four-element combined antenna array is designed. Also, an impedance transformer and power divider are designed to feed the antenna array. Also, a big combined antenna is developed with the same aperture dimensions (30 cm $\times30$ cm) as the antenna array. Then, the performances of the antenna array and the big antenna are measured and compared. Compared with the big antenna, $G_{ep}$ of the antenna array is 21% higher under the applied excitation, which indicates that the proposed method can significantly improve $G_{ep}$ of the UWB system within the prescribed aperture area. Finally, the antenna array is furthermore optimized by adjusting the distances between the elements, and $G_{ep}$ is improved by another 11%, the total improvement is 33%, and the corresponding effective potential gain is 1.49. [ABSTRACT FROM AUTHOR]

The operating frequency of future communication systems will cover unlicensed millimeter-wave bands as well as existing microwave bands. Large frequency ratio antennas that can be applied to both frequency bands simultaneously and maintain the high isolation between the two channels are difficult to design. This paper presents a new design of dual-band shared-aperture antenna based on the concept of structure reuse. The antenna consists of a patch antenna working at 3.5 GHz and a $12 \times 12$ substrate integrated waveguide (SIW) slot array antenna working at 60 GHz. The frequency ratio of this shared-aperture antenna is 17. In this design, the overall structure of the SIW slot array antenna is employed as the radiator of the patch antenna. With this new scheme, the high aperture reuse efficiency can be achieved. Meanwhile, the millimeter-wave antenna based on the SIW technology has the high-pass nature to reject the lower frequency signal. A compact microstrip resonant cell that acts as a low-pass filter is connected in series on the feedline of the microwave antenna to suppress the upper frequency signal. Thus, the channel isolation between the patch and the SIW slot array antennas can be more than 130 dB at 3.5 GHz and 65 dB at 60 GHz. [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 presents a wideband circularly polarized (CP) aperture antenna array with a specially designed feeding network. First, an irregular-cavity-backed aperture antenna element is introduced. Due to its penta-mode operation, a 72% CP bandwidth (5.3–11.2 GHz) is obtained, which is much wider than many existing unidirectional aperture-/slot-based CP antennas. In order to solve the element beam tilting problem, a novel four-element array with rotationally symmetric array arrangement and accurate out-of-phase feeding network is then proposed, which has advantages such as compact feeding structure, less gain variation, and symmetric radiation patterns. Measured results indicate that the four-element array achieves a CP bandwidth of 70.6% (5.48–11.46 GHz), a peak gain of 12.8 dBic, a 3 dB gain variation bandwidth of 69%, and averaged front-to-back ratio of 18 dB. [ABSTRACT FROM AUTHOR]

This communication presents a microstrip-fed surface-wave antenna for endfire radiation. The antenna has the advantages of high endfire gain, wide endfire gain bandwidth, and stable endfire radiation pattern. It consists of a microstrip line with air media and a dielectric cuboid. The half-mode dielectric waveguide, which is made up by the dielectric cuboid and the air substrate introduced by the microstrip line, is the radiating structure of the antenna. Fed by a microstrip line, the half-mode dielectric waveguide couples the energy continuously with a moderate phase constant, which is helpful for the antenna to realize a high endfire gain and a stable endfire radiation pattern. With a low dielectric constant, the half-mode dielectric waveguide has a stable radiation performance within a wide bandwidth. With a length of 5.76 wavelength, the antenna achieves a maximum endfire gain of 13.3 dBi at 4.75 GHz. The 1 and 3 dB gain bandwidths of the antenna is 18.1% and 37.8%, respectively. Good matching is obtained from 3 to 6.5 GHz. [ABSTRACT FROM AUTHOR]

The spatial dispersion significantly limits the operating bandwidth of a large-aperture reflectarray antenna. To achieve a wideband high-gain reflectarray antenna, a design method is proposed based on the spatial dispersion compensation concept. By introducing different resonant structures in reflectarray elements, each element has the ability to track the desired frequency–phase response, which means that the spatial dispersion of the large-aperture reflectarray antenna can be compensated by the phase dispersion of the reflectarray element over the entire frequency band. Thus, a wideband high-gain reflectarray antenna can be realized by the use of single-layer elements. As an example, a center-fed reflectarray antenna with a diameter of 354 mm ($35.4\lambda _{0}$ at 30 GHz) and a focal length to diameter ratio of 0.97 is designed and fabricated. The measured maximum gain of the prototype reflectarray antenna is 37.8 dBi with a 1 dB bandwidth of 26.7%, i.e., from 26.5 to 34.5 GHz. Compared with other high-gain single-layer reflectarray antennas, this type of antenna presents better performance. [ABSTRACT FROM AUTHOR]

This communication presents a new design of a quadri-polarization-agile aperture-coupled patch antenna array for 60 GHz applications. Four polarization states, namely, vertical linear polarization, horizontal linear polarization, left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP) can be flexibly reconfigured by dynamically switching the excitation of the corresponding port. More importantly, as the LP and CP radiations are achieved by using differential feeding and sequential-rotation feeding, respectively, the array exhibits wide impedance and axial ratio (AR) bandwidths, high polarization purity as well as symmetrical pattern with the main beam fixed at boresight. The −10 dB impedance bandwidths are better than 11.6% (57–64 GHz) for the four polarization states. The measured AR bandwidths are from 58 to more than 64 GHz for both the LHCP and RHCP. The good radiation performance together with the quadri-polarization-agile capability of this new array, as demonstrated in the communication, underlines its suitability for the future 5G communication systems, especially in a multipath propagation environment. [ABSTRACT FROM AUTHOR]

An ${S}$ -/ ${K}$ -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, $3\times 3$ metasurfaces are proposed for the ${S}$ -band radiation. To radiate the ${K}$ -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 ${S}$ -band, while an $8\times 8$ substrate integrated waveguide slot array antenna between microstrip and metasurface is designed at the ${K}$ -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 ${S}$ -band (3.2–4.05 GHz) and the ${K}$ -band (25.22–26.46 GHz), respectively. [ABSTRACT FROM AUTHOR]

A wideband frequency diversity printed-Yagi antenna array is presented. The operating band of the single port L-/S-bands antenna element can be selected by changing the states of p-i-n diode switches. The L- and S-bands work independently. A $4 \times 4$ S-band array can be constituted to a $2 \times 2$ L-band array by modifying the element apertures. This array operates at 1–2 GHz/2–4 GHz in the L-/S-bands with a fractional bandwidth of 66.7%/66.7%, which is translated into an overall tuning ratio of 4:1. The spacing of adjacent antenna elements at each reconfigurable mode is less than $0.72\lambda _{0}$ ($\lambda _{0}$ represents the free-space wavelength of the highest frequency in the operating band), which achieves no grating lobes in the radiation field. The proposed antenna array is simulated, fabricated, and tested with reasonable agreement between measurements and simulations. In this way, a rudiment of wider tuning ratio array is designed for wideband reconnaissance applications. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a triband planar shared‐aperture antenna array is proposed. The proposed antenna array could obtain similar‐shaped radiation patterns at three operating frequency bands. The total structure includes two radiation patch layers, a ground layer and a feeding network layer. Metal vias are used to excite the stacked patches, leading to three resonant frequencies. To verify the proposed antenna array, a 4 × 4 prototype with the overall size of 6.4 × 5.3 × 0.7 cm3 is fabricated and measured. The measured |S11| < −10 dB bandwidths are 13.34–13.82, 17.95‐18.61, and 23.8–25.15 GHz, and measured realized gains are 10.8, 11, and 14.4 dB at 13.5, 18, and 24 GHz. [ABSTRACT FROM AUTHOR]

Abstract: A novel single‐layer subwavelength patch element is proposed to design the circularly polarized reflectarray in Ku band. The radiation characteristics of the phase‐shifting element are investigated. The relative linearly reflected phase response curve with 360° phase coverage is achieved. A reflectarray model constructed with the proposed element is designed and fabricated, and the angular rotation technique has been employed for obtaining reflected phase curve to compensate the spatial delay. The measurements are in good agreement with the simulations. The superior bandwidth and efficiency performance have been verified. The measured gain at the center frequency of 12.5 GHz is 26.5 dBi, corresponding to the aperture efficiency of 51.9%, and the obtained 1 dB gain and 3 dB AR bandwidth can reach 24.8% and 35.2%, respectively. [ABSTRACT FROM AUTHOR]

A dual-port, dual-band, and circularly polarized (CP) radio frequency identification reader antenna is designed to operate at both ultrahigh frequency (UHF) and lower ultra-wideband (UWB) bands for indoor positioning systems. In conjunction with a properly selected quadruple feed network, a shared aperture using the concept of hybrid mode is utilized for broadening the antenna bandwidth. The concept is demonstrated to achieve a high gain, wideband, and CP operation within a low profile. The measured overlapping 3-dB axis ratio (AR) bandwidth and 10-dB impedance bandwidth for the UHF band ranges from 0.918 to 0.926 GHz with a minimum in-band antenna gain of 9 dBic. The measured overlapping 3-dB AR bandwidth and 10-dB impedance bandwidth covers from 3 to 5.2 GHz with a minimum in-band gain of 9 dBic in the lower UWB band (i.e., 3.1–4.8 GHz). The gain suppression near the two wireless local area network bands (i.e., 2.45 and 5.8 GHz) is more than 20 dB. The isolation between two ports is larger than 25 dB over the UHF and lower UWB bands, respectively. [ABSTRACT FROM AUTHOR]

In this communication, solutions are developed for gain and bandwidth enhancement of a ridge gap waveguide (RGW) H-plane horn antenna. Intrinsic features of RGW allow us to introduce a simple transition at the antenna aperture making its impedance matching with outer space easier, leading to antenna bandwidth enhancement. Two transitions, stepped and tapered, are introduced. The proposed transitions are fully designed as a part of horn flared part and do not introduce any expansion to the antenna length, contributing to its compactness. Furthermore, the modified form of the proposed RGW H-plane horn in which the antenna aperture is squinted is also presented. In this form, the backward radiation is reduced leading to 2 dB gain enhancement. [ABSTRACT FROM AUTHOR]