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In this letter, a dual-polarized frequency-selective absorptive structure is presented with two wideband transmission windows. The transmission windows are achieved within a wide –10-dB reflection band. At the frequencies of the passbands, the out-of-phase currents are excited without flowing through the lossy elements. Therefore, the passbands can be obtained with high transmittance. Moreover, only four resistors are loaded on each unit cell to consume the out-of-band reflective wave. By combining lossy flower-shaped and lossless arrays together, the desired dual-band and low reflection performances can be realized. Within the operating band, the reflection is below –10 dB with the fractional bandwidth of 127%. Meanwhile, around 6.5 and 12 GHz, the passband widths are 39% and 40% and the corresponding insertion losses are 0.07 and 0.1 dB, respectively. Finally, the fabricated prototype is measured to demonstrate the feasibility of the presented method.

A low-profile differentially fed dual-polarized antenna with high gain and isolation is proposed for fifth-generation (5G) microcell communications. By introducing two pairs of symmetrical meandering conductors to connect both ends of the radiating cross slots, a compact-size antenna with wide bandwidth can be achieved. By further adopting an artificial magnetic conductor-backed (AMC) reflector that is arranged below the radiating patches with a distance of 6 mm, the antenna profile can be reduced from $0.25\lambda _{c}$ to $0.13\lambda _{c}$ (where $\lambda _{c}$ is the free-space wavelength at the center frequency), while both the gain and frequency bandwidth are also enhanced. Furthermore, owing to the orthogonal differentially fed structure, the antenna element displays a high port isolation of 37 dB. Finally, by meticulously designing the feeding network, much narrower beamwidth can be yielded, and hence, the unidirectional gain is further improved. The measured results show that a lower-frequency bandwidth of 13.5% (3.26–3.73 GHz) with a gain of 15.7 ± 0.1 dBi and upper-frequency bandwidth of 7.6% (4.68–5.05 GHz) with 15.55 ± 0.05 dBi gain can be obtained by the proposed antenna array. In addition, port isolation better than 28 dB and stable radiation patterns can be achieved. With the aforementioned characteristics, the proposed antenna is a good candidate for future 5G microcell communications.

This paper presents a cross dipole antenna for the fifth generation (5G) sub-6 GHz dual-band applications. The proposed antenna mainly consists of eight copper radiating patches, eight parasitic patches, and a reflector. The proposed antenna can achieve a ±45° polarization characteristic. The overlapped bandwidth is 2.77-5.31GHz, and the corresponding gain varies from 7.6 to 8.4 dBi. The gain increases with increasing operating frequency. Besides, the cross polarization level is less than -28 dB while the port isolation is larger than 26 dB.

In this letter, a new frequency-selective absorber is presented that has wideband transmission/absorption/reflection reduction responses. The presented absorber is completed by lossy cross-dog-bone and lossless second-order frequency-selective surfaces. The modal interaction pole generated by the lossy array is employed to achieve a wideband transmission. Three absorption bands are combined to realize a continuous stopband with high absorptivity. Furthermore, the improved absorber structure is investigated to reduce the strong reflection between the absorption and transmission bands. The 10 dB reflection reduction is obtained with a fractional bandwidth of 126.4%. Meanwhile, the –3 dB fractional passband width is 41.3% with minimum insertion loss of 0.37 dB. The absorption bandwidth of 91.5% is provided with at least 90% absorptivity. The distance between the lossy and lossless layers is only 0.08 $\lambda _{L}$ at the lowest operating frequency. Finally, the proposed design is validated by a good agreement between the numerical simulations and experimental measurements.

This contribution presents a novel 3-D circular conformal MIMO antenna system composed of three magneto-electric dipoles (MED) antennas. The single MED element was delicately designed to include one main (lower-band) dipole and two auxiliaries (upper-band) dipoles in order to achieve the dual-band radiation. The proposed MED owns a low-profile conformal geometry but features a wide H-plane beamwidth (minimum 103°). By embedding the metamaterial of the broadside-coupled E-shaped unit cells into the magnetic dipole, the height of MED can be dramatically reduced by 37.2% as compared with the conventional ones. Meanwhile, the two U-shaped notches together with a rectangular notch were included onto the E-dipole to create a band-notch, which offers the anti-interference capability to the ubiquitous 2.4-GHz signal of the wireless local area network. According to the measurement results, the MED element exhibits an impedance bandwidth of 54.2% (1.68-2.93 GHz) with a stable gain of 6.05± 1.15 dBi in the lower band and 9.2% (3.32-3.64 GHz) with 5.71 ± 0.7 dBi in the upper band, respectively. Moreover, the three-element MIMO system provides quasi-omnidirectional coverage in the H-plane from 1.68 to 3.64 GHz. The outstanding performance metrics validate the proposed ME dipole antenna that is well suited for the future sub-6-GHz fifth-generation MIMO mobile base stations.

The design of a compact circular polarization (CP) electrically small antenna (ESA) is carried out and presented in this paper. The designed antenna consists of a planar circuit board (PCB) on which two 3-dB hybrid couplers are fabricated for providing left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) waves, and two ceramic substrates covered by thin metal films with the high dielectric constants of 20.5 and 39 and the sizes of 25x25x6 mm and 18×18×4 mm, respectively. This compact CP ESA can realize a coverage of ±75° elevation angle with gain above -4dB in the frequency band of 1518 - 1525 MHz for RHCP and in the band of 1668 - 1675 MHz for LHCP, and a coverage of ±60°elevation angle with gain above - 2dB in the band of 1575.42±1.023 MHz for RHCP.

A circularly polarized (CP) antenna based on metasurface with simple structure is proposed for 5G millimeter-wave (mmw) applications. This antenna mainly consists of three layers. Square patches with periodic rhombus grooves are placed on the top of the first layer. A pair of substrate integrated waveguide (SIW) feeding networks are orthogonally arranged in the second layer and third layer, respectively. Simulated experiments demonstrate that an overlapped frequency bandwidth of 5.4% (27.1-28.6 GHz) as well as a 3-dB axial ratio (AR) bandwidth of 7.9% (26.8-29 GHz) can be achieved in dual circularly polarized directions.

An ultra-wideband double-ridged horn antenna is proposed in this paper. By utilizing the ridge structure, the bandwidth of the horn antenna is broadened. Prototype of the horn has been fabricated to verify the performance. The horn antenna impedance bandwidth (VSWR

In this paper, a double-mode orbital angular momentum (OAM) antenna is proposed. By using an octagonal microstrip ring antenna with a matched load can generate orbital angular momentum (OAM) beams with different OAM modes at the same frequencies. When the inner ring is fed, this antenna can generate an OAM mode of $l=1$ at 5GHz. Similarly, when the outer ring is fed, vortex waves with $l=2$ can be generated. Because of its low profile and small size, this antenna is more potential in wireless communication, mobile devices, remote sensing and so on.

A beam deflection reconfigurable antenna based on the metamaterial is proposed for macro station or integrated small base station applications. The proposed antenna consists of a cylindrical dielectric resonator antenna (CDRA) and a reconfigurable 2 × 2 array of metamaterial. The proposed antenna can steer the main beam by 20°, 43°, −26°, −48° in the E-plane over 3.6-3.8 GHz according to the simulation results.

A novel magneto-electric dipole antenna with wide H -plane beamwidth, triple-linear polarisation and frequency reconfiguration is proposed for 5G communications. In this study, the radiated dipoles are designed with the arc-shaped planes to exhibit wide H -plane performance. A bent cross-dipole feed with PIN diodes and varactor diodes inserted into its four arms at different altitudes is utilised to excite and control the antenna. Consequently, a measured wide beamwidth ranging from -67° to 67° can be achieved in H -plane. In addition, the height of the proposed antenna decreased about 30% due to the bent designs. Finally, by controlling the PIN diodes and varactor diodes, the three kinds of linear polarisations and frequency reconfiguration functionalities for 2G/3G/LTE/5G applications can also be easily obtained. With the above-mentioned features, the proposed antenna well suits for intelligent base-station communications.

In this paper, a dual-polarized wide-beamwidth magneto-electric (ME) dipole antenna for the fifth generation (5G) mobile communications is proposed. The proposed ME dipole antenna is printed on several dielectric substrates for easy fabrication. By applying a quadrate fence around the ME-dipole antenna, wide-beamwidth characteristics for both E- and H-planes can be obtained in dual linearly polarized directions. The proposed antenna realizes a half-power beamwidth (HPBW) of 129.1 ° in E-plane and another 100.4° in H-plane at 3.4 GHz, while 151.6° in E-plane and 94.2° in H-plane at 4.9 GHz can also be achieved. An overlapped impedance bandwidth (

In this paper, a tri-polarized MIMO antenna with diverse radiation properties for the 5G-V2X vehicular communication is proposed. The design consists of an omnidirectional monopole unit and two pairs of loop radiator dipoles. By loading eight pairs of double inverted L-shaped elements, the directional dipoles get wide-beamwidth characteristic for both E-plane and H-plane. Moreover, the larger inverted L elements lower the elevation angle of the main radiative direction of the monopole, which results in gain enhancement in the azimuth plane. For the directional cross-dipoles unit, two impedance bands reach 34.36% and 19.62% (VSWR

A novel linearly dual-polarized antenna array with triple elements is proposed for beamwidth reconfigurable base-station communications. By cutting off the arc-shaped corners on the radiated patches, the single dual-polarized antenna unit can obtain a wide bandwidth of 78.4% for SWR ≤ 2, ranging from 1.63 to 3.73 GHz for 2G/3G/LTE and 3.5-GHz C -band (3.4–3.6 GHz) applications. In addition, with the box-shaped reflector and the inherent characteristic of the ME dipole antenna, the average gain of the dual-polarized antenna element is about 11.5 dBi. Finally, by employing a two-stage circuit with several power dividers, a three-element antenna array with a widely adjustable beamwidth in both the $E$ -plane and $H$ -plane is investigated, which could meet the demand of the future smart applications.

In this article, a novel broadband end-fire circularly polarized antenna is presented. It comprises a diamond-shaped shorted parallel-plate cavity (DSPC) and planar symmetrical conductor arms (PSCA). The DSPC and PSCA serve as the electric and magnetic dipole, respectively. By adjusting the aperture of DSPC and bending angle of PSCA, the impedance bandwidth and the axial-ratio bandwidth are greatly improved. Meanwhile, the end-fire circles are employed to improve the gain of an antenna. The overall size of the antenna is 35.5 mm × 38.2 mm × 2 mm, equal to 0.98 λ0 × 1.05 λ0 × 0.055 λ0. The measured results show that the realized impedance bandwidth for S11 ≤ –10 dB is 14.1% (7.63–8.79 GHz) and 3-dB AR bandwidth is 16.4% (7.57–8.92 GHz). A good agreement between the simulated and measured results is obtained.

A dual-band beam-sweeping antenna based on two independent cylindrical active frequency selective surfaces (AFSSs) is proposed in this paper. This antenna is composed of a dual-band omnidirectional monopole antenna operating at 2.45 and 5.2 GHz and two cylindrical AFSS screens. The dual-band omnidirectional monopole antenna is designed as a radiating source and surrounded by the proposed two cylindrical AFSS screens. The unit cells of the two proposed AFSS screens consist of two metallic crosses connected by a pin diode vertically. By switching the pin diodes, the transmission and reflection characteristics of unit cell of the two AFSS are investigated, respectively, at their own operating frequency. This leads to the variation of the radiation pattern when the cylindrical AFSS screens are loaded around the monopole antenna. Therefore, by switching the pin diodes with specified combinations, the dual-band beamforming antenna with multiple discrete states can be achieved at 2.45 and 5.2 GHz.

A beam-tilting antenna with negative refractive index metamaterial (NRIM) loading is proposed for WLAN applications. The proposed antenna is composed of a double-feed dielectric resonator antenna (DRA) and 1 × 4 NRIM array, which are fixed over and in the middle of the DRA. The proposed NRIM unit cell comprises a fractal cross-ring resonator structure and performs a negative refractive index in the band from 5 to 5.5 GHz. When the electromagnetic (EM) waves enter a medium with a negative refractive index, the direction of propagation of the EM wave can be changed. Therefore, beam-tilting can be implemented by using the DRA cooperating with the proposed NRIM array. The simulation and experimental results show that the beam-tilting antenna can steer the main beam by ±38° in the xoz -plane over 5–5.5-GHz band. The reflection coefficient of the antenna is better than −10 dB in the band from 5 to 5.5 GHz. Furthermore, the measured results have a good agreement with simulated ones.

A novel wideband antenna array with coplanar waveguide series feed is proposed in this letter. By etching a symmetrical circular slot (SCS) structure on the bottom metallic layer, the impedance characteristic of the antenna array is greatly improved. Meanwhile, the gain of the antenna array at the lower band is improved by inserting another SCS in the center of the two array elements. The measured results show that the impedance bandwidth of the proposed antenna array is from 2.04 to 3.74 GHz (the relative bandwidth is 58.8%). Moreover, the maximum gain reaches 6.9 dBi.

In this paper, a microstrip array antenna with orbital angular momentum is proposed. Twelve identical printed dipole antennas with microstrip balun feeder are arranged in a dodecahedron cylindrical substrate. By changing the value of the phase difference between successive elements, five kinds of electromagnetic waves of different modes of orbital angular momentum are generated. The simulation results show that the expected results have been achieved with the modalities of OAM 0, 1, 2, 3, 4. Consequently, the proposed orbital angular momentum antenna has a promising prospect.

This paper proposed a dual-polarized broadband horn antenna for mm-wave 5G application. The operating frequency of the antenna proposed in this paper is 18 to 40GHz. The antenna with VSWR 10dB and HPBW>20° is presented, and the radiation patterns maintain a good symmetry in full band. And this antenna has been tested and used in practical applications.

A polarization switchable ultra-wideband horn antenna with feeding network is designed and implemented. A single antenna can realize four switchable polarization modes (vertical polarization, horizontal polarization, left-hand circular polarization, and right-hand circular polarization) with ultra-wideband characteristics in the microwave and millimeter wave frequency band by an electronically controlled mechanical switch. TTL (Transistor-Transistor Logic) level is adopted as controlled electrical signal. The antenna can significantly improve test efficiency by avoiding manual switching of the antenna polarization mode. The presented antenna has a super wide bandwidth of 9.3GHz, worked well from 0.7GHz to 10GHz. Measured results for VSWR, radiation pattern, and gain of the designed horn antenna are provided.

© 2018 IEEE. In this paper, we presented a dual-band dual-polarized (DP) omnidirectional antenna for 2G/3G/Long Term Evolution (LTE) indoor communication systems. Two modified cones compose the vertical polarized (VP) unit, which exhibits good omnidirectional radiation performance and achieves a wide impedance bandwidth. The loop antenna and the printed circular dipole arm arrays are arranged on the top end and middle end of the VP unit, respectively. They are connected by a commercial diplexer as the horizontal polarized (HP) units. Simulated results indicated that an impedance bandwidth of 790 MHz-1.14 GHz and 1.72-3.51GHz can be achieved for VP while another one of 806-980 MHz and 1.68-2.99 GHz is also obtained for HP. In the azimuth plane, omnidirectional radiation patterns for both VP and HP are achieved. For the lower and upper frequency bandsmore than 1 dBi and 3 dBi antenna gain are realized for both of the VP and HP radiations, respectively. Better port-to-port isolation, low cross polarization and little gain variation are also acquired.

In this paper, we presented a novel low-profile differentially feeding dual-polarized antenna adopting wideband artificial magnetic conductor (AMC) reflector for the fifth generation (5G) base-station communications. There are some winding inductors arranged at both ends of the cross slots, which result in a small-size radiating patch as well as a wide bandwidth. Both impedance bandwidths of 47.3% (3.28–5.31 GHz) and 47.2% (3.29–5.32 GHz) can be achieved for Ports I and II, respectively. Due to differentially feeding scheme, a high port isolation of below -40 dB during the working frequency band is obtained. In addition, thanks to the AMC structure, the profile of proposed antenna can be reduced from 18 to 9.5 mm ($0.13{{\lambda }_{c}},{{\lambda }_{c}}$ is the free-space wavelength at the center frequency).

This letter presents a new design of a Fabry–Perot resonator antenna (FPRA) with a wide gain bandwidth. A double-layered dielectric superstrate, which produces a reflection phase curve versus frequency with a positive slope, is used as a partially reflective surface (PRS) to enhance the bandwidth of the FPRA. For a physical insight, the PRS is analyzed by using the transmission line theory and Smith Chart. Experimental results demonstrate that the antenna has a 3-dB gain bandwidth over 13.5–17.5 GHz, relatively 25.8%, with a peak gain of 15 dBi. Furthermore, the gain band is overlapped well by the impedance band for the reflection coefficient ( ${ S}_{11}$ ) less than $-$ 10 dB.

A novel low-profile and wideband dual-polarized magneto-electric (ME) dipole antenna is presented for base-station application. The proposed antenna is excited by two orthogonal Γ-shaped probes, which can aslo improve its isolation. The isolation between the two ports is better than 30 dB over the operating frequency. By employing the metamaterial loadings which are fully arranging inside the magnetic dipole, the height of the proposed antennna can be decreased from 28 to 20 mm. Due to the specially designed notches etched in the radiated dipoles, an impedance bandwidth of 69.2% ranging from 1.71 to 3.60 GHz, together with a notch-band frequency bandwidth ranging from 2.35 to 2.55 GHz can be achieved.

A high-gain beam switching antenna based on frequency selective surfaces (FSS) operating at 5.2 GHz is presented. In this design, a monopole is used as radiating source and surrounded by four columns of FSS screens and four metallic sheets. The FSS unit cell comprises two metallic crosses and a pin diode embedded between them. The transmission characteristics of the FSS unit cell are investigated when the state of the pin diode is ON and OFF. By changing the states of the pin diodes in the FSS screens, beam switching can be achieved at 5.2 GHz. The metallic sheets are used to improve the gain of the antenna. Simulation results show the gain of the beam switching antenna with metallic sheets has been enhanced 7.2 dB compared to that without metallic sheets.

The auxiliary differential equations on the intermediate variables which are introduced to rewrite the constitutive relation for dispersive bi-isotropic media are established. Then the discrete time-domain recursive formulation to calculate the intermediate variables is obtained by using the Newmark-Beta method, and the Newmark-FDTD formulation for dispersive bi-isotropic media is developed. The reflection and transmission coefficients including copolarization and cross-polarization of a dispersive chiral slab and the bistatic radar cross-section of dispersive chiral sphere are simulated. The numerical results demonstrate the validity and feasibility of the proposed method.

This paper presents a novel design of a Fabry-Perot (FP) resonator antenna with a wide gain bandwidth in X band. The bandwidth enhancement of the antenna is attributed to the positive reflection phase gradient of an electromagnetic band gap (EBG) structure, which is constructed by the combination of two complementary frequency selective surfaces (FSSs). To explain well the design procedure and approach, the EBG structure is modeled as an equivalent circuit and analyzed using the Smith Chart. Experimental results show that the antenna possesses a relative 3 dB gain bandwidth of 28%, from 8.6 GHz to 11.4 GHz, with a peak gain of 13.8 dBi. Moreover, the gain bandwidth can be well covered by the impedance bandwidth for the reflection coefficient ( ${\rm S} _{11}$ ) below $-10~{\rm dB}$ from 8.6 GHz to 11.2 GHz.

A wideband ring-slot coupled patch antenna is presented in this paper. A microstrip line feeding network is used for impedance matching. Additionally, in order to depress the backward radiation caused by the resonance of the ring-slot, a reflector is introduced to obtain unidirectional radiation patterns, while a dielectric cover is adopted to alleviate the deterioration in impedance caused by the reflector. A prototype is fabricated and measured. The measured results are in good agreement with those simulated, which indicates that the antenna operates well with a relative bandwidth of 55% for reflection coefficient less than −10 dB, an enhanced gain of 8–11 dBi, unidirectional radiation patterns, as well as low cross-polarization.

A new wideband and high-gain dielectric resonator antenna (DRA) is proposed. Three cylindrical dielectric resonators (DRs) with difierent materials and difierent sizes and a metallic cylinder are designed to obtain a wideband bandwidth and a high gain. The stacked structure provides a wideband bandwidth, and the cavity formed by the metallic cylinder provides a high gain. The measured results demonstrate that the proposed DRA has a wide bandwidth from 5.4 to 7.0GHz with VSWR less than two and a gain around 11dBi, covering the frequency range of 26%. The experimental and numerical results are discussed and compared with each other, showing a good agreement between them.

In this work, we proposed a beam-tilting antenna based on metamaterial loading. The proposed antenna consists of a dielectric resonator antennas (DRA) and 1 × 4 array of negative refractive index metamaterial (NRIM) unit-cells fixed above the DRA. The proposed NRIM unit-cell comprises of a fractal cross ring resonator structure which performs a negative refractive index during band of 5–5.5 GHz. The direction of propagation and phase can be changed when EM waves entering a media of negative refractive index. Hence, beam-tilting can be implemented by using proposed NRIM unit-cells with DRA. The simulation and experimental results show that DAR can steer the main beam by 38° in the xoz-plane over 5–5.5 GHz band. The S 11 of antenna is better than −10 dB from 5 GHz to 5.5 GHz. A good agreement is found between the simulated and measured results.

Physical optics (PO) or Fresnel-Kirchhoff theory forms the base to solve the problem of diffraction over terrain or buildings, particularly when the terrain or buildings can be modeled as knife edges. Because the numerical integration required to solve the realistic problems is very time-consuming, physical optics is not commonly used in the original formulations for developing the related software products. In order to increase the computational efficiency, a number of assumptions and simplifications have been made. In this presentation, Fresnel-Kirchhoff theory is briefly reviewed, the assumptions and simplifications made for improving the computational efficiency is explained and clarified, the prediction accuracy is evaluated through the comparison between prediction and measurement, the inherent drawbacks of the prediction PO based and its limitations in application are discussed, and possible improvement of the prediction algorithm and procedure is proposed.

An effective modeling of wave propagation over the spherical earth surface is of importance for target tracking, radar detection and wireless system analysis. This topic has been intensively studied in the past several decades. Meanwhile, the uniform theory of diffraction (UTD) for smooth convex surfaces has been developed and widely used in electromagnetic radiation and scattering. However, applying UTD to an effective analysis of propagation over a spherical earth surface still remains a challenge so far. This paper discusses a UTD based prediction of propagation loss over a spherical earth surface. It is shown that the current UTD solutions for some scenarios in the point-to-point propagation over a curved earth could be invalid when the source and observation points are located in the surface boundary layer or close to the surface boundary layer. These scenarios are in the situations that could not be defined as scattering, radiation and coupling, that is, could not be characterized by any of current UTD formulations. On the other hand, when the source and observation points are far away from the surface boundary layer, a UTD based propagation prediction can be undertaken, with its correctness and effectiveness validated through a comparison between our results and those previously published in the literature.

In this paper, a capacitive-fed resonator is designed and investigated to excite the small bent planar monopole antenna. The proposed principle of bandwidth enhancement is verified by a 2.4 GHz antenna design. The enhanced bandwidth of the small antenna is 200 MHz, within a size of 18.6×24 mm2 (about 0.15 λ ×0.19 λ ).

A compact high-gain patch antenna based on near-zero index metamaterial (NZIM) superstrate lens operating at 2.44 GHz is proposed. A single layer NZIM superstrate with unit-cell periodicity of 3 × 4 is designed and suspended above a patch antenna at a very close distance of 0.097 λ. Simulation results show that the NZIM superstrate could converge the electromagnetic wave radiated by the antenna to enhance the radiation gain. The proposed single layer NZIM superstrate provides a gain enhancement of 2.3 dB at 2.44 GHz to a conventional patch antenna.

A metamaterial composed of two face-to-face symmetrical split-ring resonators and a cross-wire located on each side of a dielectric substrate is demonstrated. The retrieved refractive index from the scattering parameters show that the proposed structure can exhibit a broadband negative refraction passband from 41GHz to 62GHz with very low dispersion from 47GHz to 57GHz. In addition, the retrieved refractive index is examined by Kramers-Kronig relations. The metamaterial with such a broadband negative index and low dispersion will be valuable and applicable in the wavelength division multiplex system.

A dual-band reconfigurable radiation pattern antenna based on active frequency selective surfaces (AFSS) is presented. This antenna is composed of a dual-band omni-directional patch antenna and two cylindrical AFSS with the operating frequencies of 2.45 GHz and 5.2 GHz, respectively. The unit-cells of the proposed AFSS consist of the two metallic crosses connected by a pin-diode vertically. The transmission characteristics of the proposed AFSS at both frequencies are investigated. Results show that by switching the pin-diodes, the unit-cells of two AFSSs present the states of transmission and reflection, respectively, at their own operating frequency. This leads to the variation of radiation pattern when the cylindrical AFSS is loaded around the patch antenna. Therefore, by switching the pin-diodes with specified combinations, the dual-band beamforming antenna with multiple discrete states can be achieved at 2.45 GHz and 5.2 GHz.

In this paper, a dual-band CPW-fed antenna is designed with wide bandwith (BW) tunability. By using the odd-/even-mode theory, the resonant characteristics of the radiating element is vividly analyzed based on equivalent circuit models and design curves. There are four resonances, the 1st of which performs as a parasitic resonance. The 2nd resonance produces the first operating band while the 3rd and 4th resonances construct the second band. By spliting the second operating band into two narrow bands, a tri-band antenna can be produced. The fabricated dual-band antenna works at 2.39 GHz and 5.26 GHz with BW of 14.9 % and 23.5 %, respectively. The mid-band reflection coefficient in each band is better than − 18 dB.

A time domain technique based on numerical inversion of Laplace transform is extended and applied to transient analysis of pulses reflected from a Lorentz half space both for TE and TM cases. Its correctness and effectiveness are validated by comparing our results with those published in the literature. With this technique, the TM case when the incident angle is equal to 450 does not need to be processed separately and can be treated as a general case for any incident angle. This technique brings good accuracy in both late and early time, a simple algorithm, short calculation time, small required memory size and readily controlled error.

The re∞ection of short duration electromagnetic pulses from dielectric media is of interest in diverse technological applications, e.g., geophysics, material science and biomedical engineering. In this paper, the time domain pulse re∞ection from a dispersive lossy dielectric half space is investigated. The properties of a half space are described in frequency domain by the Debye and Cole-Cole models, respectively. The two models are commonly used to capture the relaxation-based dispersive properties. First, transient re∞ected pulses are analyzed and waveform parameters are estimated. Then, based on the estimation, the relationships between the waveform parameters of re∞ected pulses and the properties of dispersive material as well as incident angles are discussed. Meanwhile, the results obtained with the Debye model are compared to those obtained with the Cole-Cole model. The application of these results to material characterization and diagnosis is explored. There is excellent agreement between our results and those in the literature, which validates the correctness and efiectiveness of this work. Our technique is based on the numerical inversion of the Laplace transform, leads to good accuracy, and has a simple algorithm, short calculation time, small required memory size, readily controlled error and wide range of applicability. The knowledge of material properties is required in various technological flelds, such as geophysics, material science and biomedical engineering. The characterization of bulk materials would be the most direct way to acquire this knowledge and greatly helpful to understand the underlying physics at the microscopic level, which is much more complicated in comparison with the existing formula- tions of the bulk efiects. A typical approach to bulk material characterization is to examine re∞ected electromagnetic pulses from the interface between free space and the investigated material. Many kinds of materials show the relaxation-based dispersive properties that are commonly captured by the Debye (1) and Cole-Cole (2) models. The transient analysis of pulses re∞ected from a dispersive interface can be conducted in frequency domain flrst. Then the results in time domain may be ob- tained by carrying out a numerical Fourier transform of the frequency domain response. However, this is very time consuming since a wide frequency range needs to be considered. Furthermore, it is preferable to solve the problems directly in time domain under certain circumstances. The flnite difierence time domain (FDTD) technique can be applied to this problem, but computation costs can be high under some conditions. Rothwell (3) worked out the time domain re∞ection coe-cients of a Debye half space for both horizontal and vertical polarizations that involve exponential and modifled Bessel functions and require convolution operations to evaluate. To our knowledge, the time domain re∞ection coe-cient of a Cole-Cole half space for any polarization has been not avail- able so far. It is the purpose of this paper to develop a new technique for transient analysis of pulse re∞ection from Debye and Cole-Cole media, and apply this technique to waveform parameter estimation and material characterization. This technique is based on the numerical inversion of the Laplace transform and has several signiflcant advantages.

In this paper, a beam switching antenna with a novel active frequency selective surface (AFSS) is proposed at 5.2 GHz. The antenna is composed of an omnidirectional patch antenna and AFSS. The AFSS is made up of 6 columns, each with 2 unit cells, which are placed vertically around a patch antenna to form a hexagonal wall. To steer beam of the antenna, high frequency pin diodes are precisely inserted into the AFSS to reconfigure electromagnetic (EM) response of surfaces. The reflection and transmission characteristics of the proposed AFSS unit cell are investigated. The simulation results show that the transmission and reflection bands of AFSS unit cell can be changed by setting diodes on and off. This new AFSS can be used to implement a sweeping radiation pattern at all azimuth angles. The antenna can sweep the entire azimuth plane in six steps and effectively operate over a bandwidth of more than 500 MHz.

A high gain broadband antenna using a cylinder hollow-cavity microstrip structure with multilayer H-shaped slots is presented, which can be realized by microwave multi-layers technology (MLT). The measured impedance bandwidth of the proposed antenna is 32.3% with the reference of S11−10dB, and the measured gain of the antenna is 5.75dBi @ 16.1GHz and 6.2dBi @ 20GHz, which indicates a low gain fluctuation in the whole bandwidth of the antenna.

In this paper, a beam switching antenna based on a new active cylindrical frequency selective surface (ACFSS) is proposed at 2.45 GHz. The proposed active frequency selective surface (AFSS) unit cell consists of the two crosses and a high frequency pin diode. The pin diode is precisely inserted between two crosses. The reflection and transmission characteristics of the proposed AFSS unit-cell structure are investigated. Results show that by controlling states of pin diode, the transmission and reflection bands can be changed. This new ACFSS is used to implement a sweeping-beam flexible antenna covering all azimuth angles. The simulated results confirm the concept of the proposed configuration. This antenna can effectively operate over a bandwidth of more than 500 MHz. Moreover, the achieved back-lobe level for the directional radiation pattern is about −12.5 dB at the frequency of 2.45 GHz.

An effective modeling of wave propagation over the spherical earth surface is of importance for target tracking, radar detection and wireless system analysis. This topic has been intensively studied in the past several decades (V. A. Fock, Electromagnetic Diffraction and Propagation Problems, Oxford: Pergamon, 1965). Meanwhile, the uniform theory of diffraction (UTD) for smooth convex surfaces has been developed and widely used in electromagnetic radiation and scattering. However, applying UTD to an effective analysis of propagation over a spherical earth surface still remains a challenge so far.

This paper presents a new design of a Fabry-Perot resonator antenna (FPRA) with a wide gain bandwidth working in Ku band. A dielectric-based electromagnetic band-gap (EBG) structure, which consists of two dielectric substrates and can produce a reflection phase curve versus frequency with a positive slope, is proposed to enhance the bandwidth of the FPRA. For a physical insight of the working principle, the EBG structure is analyzed by using the transmission line theory. The experiments are carried out to confirm the design of the wideband FPRA, and the results demonstrate that the antenna has a 3 dB gain bandwidth over 13.5 GHz to 17.5 GHz, that is, 25.8% of the total bandwidth, with a peak gain of 15 dBi. Besides, the gain band can be covered well by its impedance band for the reflection coefficient (S 11 ) less than −10 dB. The proposed method is effective, and can be easily applied to designs at other frequencies.

In this paper, a novel ultra-wideband (UWB) bandpass filter (BPF) with a narrow notched band is proposed. The proposed notch-band UWB BPF consists of two symmetric multiple-mode resonators (MMRs) and four defected ground structures. The design of the proposed notch-band UWB BPF is confirmed by simulation with a full wave electromagnetic simulator. The passband of the implemented filter covers the range of 2.8–11GHz, and the insertion loss of the notched band within the UWB passband is 15.65 dB at 5.7 GHz.

In this paper, a high-gain reconfigurable dielectric resonator antenna (DRA) at the millimeter wave (MMW) frequency band is presented. This antenna offers a gain enhancement 6dB over a conventional DRA and a reconfigurable radiation pattern in the entire azimuth plane. To produce these features, the proposed antenna uses a new reconfigurable frequency-selective surface (FSS) unit-cell. The reflection and transmission characteristics of the proposed FSS unit-cell structure are investigated. Results show that by controlling the state of diodes in each unit-cell, the transmission and reflection bands can be changed. Therefore, by changing state of the diodes, beam steering can be achieved in the entire azimuth plane.

For massive MIMO systems, it is very challenging to have the large-scale antennas for a compact base station. This paper presents a 36 sub-sectors for a compact millimeter-wave base station. The antenna array for each sub-sector is comprised of 16 planar high-gain dielectric-loaded antipodal linearly tapered slot antenna (ALTSA) elements arranged in a 4×4 configuration. Down to 36 feed ports are required in a base station with 36×16 antennas. The realized gain of the antenna array is 25.6 dBi, and the half-power beam widths (HPBW) are 10.7° and 5.3° in H-plane and E-plane, respectively.

A novel design of an electromagnetic band gap (EBG) resonator antenna with a wide gain bandwidth at Ku band is presented. The bandwidth enhancement of the antenna is attributed to the positive reflection phase gradient of the EBG structure, which is generated by the combination of two dielectric substrates with different dielectric constants and thicknesses. The calculated results indicate that the antenna possesses a relative 3dB gain bandwidth of 26%, from 13.6GHz to 17.7GHz, with a peak gain of 15dBi, which can well cover the whole impedance bandwidth for the reflection coefficient (S11) less than -10dB, from 13.9GHz to 17.7GHz. The design method developed here is significantly effective, and can be easily adopted for antenna designs at other frequencies.