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In this article, a metal-only reconfigurable reflectarray antenna (RRA) is proposed for generation of diversified circular-polarization (CP) focused beams and mode-agile vortex beams in the X-band. The proposed RRA element has the 3-D metal-only configuration, which consists of three staircases with different heights, a turntable, a latch, and a base. By rotating the proposed RRA element in 45° steps, the ability of 1-bit phase quantization with orthogonal linear polarization (LP) reconfigurability can be realized. Then, a 26 × 26-elements reconfigurable reflectarray antenna feeding by a linear polarization horn antenna is designed to enable free conversion of line-to-circle polarization at the array level. Full-wave simulations show that the diversified circular-polarization beams can be synthesized by adjusting the aperture element distribution. Furthermore, a manually reconfigurable reflectarray antenna prototype is fabricated to obtain the actual performance of the synthetic LHCP focused beams. The measured maximum gain of the LHCP beams is 27.1 dBi, with the aperture efficiency of 24.2% where the beam point at 20°, and the 1-dB gain bandwidth is 18.0% (9.3 GHz − 11.1 GHz). Finally, mode-agile vortex beams can also be realized by using the proposed reconfigurable reflectarray antenna, and the simulated results show that the mode purity of vortex beams are all above 35% in different modes, and the maximum gain of the vortex beams is 21.1 dBi, with aperture efficiency of 6.1% where the mode of vortex beams is −1. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to accurately simulate the low frequency electromagnetic scattering of a homogeneous dielectric object in layered medium. The N-Muller surface integral equation (SIE) is utilized for accurate electromagnetic modeling at low frequency with a properly designed coefficient to cancel frequency singularity. Matrix-friendly layered medium Green's functions are adopted and integrated into SIE to account for the effects of the inhomogeneous background. By using Galerkin method and rooftop basis functions, a well-conditioned impedance matrix is obtained and a rapidly converging iterative solution is achieved for low frequencies. Numerical results are provided to validate the proposed method and investigate its properties. [ABSTRACT FROM AUTHOR]

A millimeter wave dielectric resonator antenna (DRA) array with high-gain and high-selectivity filtering response is proposed, which is composed of stacked feeding network and stacked DRA. The stacked feeding network consisting of two layers of thin substrate has the efficient characteristics to expand and integrate. The band-pass filter formed by complementary split ring resonator (CSRR) structure generates radiation nulls at the edge of the high-frequency band. With the improved filtering stubs loaded at the end of the H-shaped microstrip power divider, a radiation null at the edge of the low-frequency band is obtained and the roll-off degree at the edge of the high-frequency band is improved. By embedding the metal column in the fork-shaped stub, the suppression level of the low-frequency stopband is improved. A prototype of the proposed DRA array is fabricated and measured, which shows 7.2% relative bandwidth and a stable directional pattern in the range of 26.28–28.25 GHz with an average gain of 9.57 dBi. And an out-of-band suppression level of 18 dB is achieved. The DRA array can be applied for 5 G millimeter wave band to support high-speed communications at short distance. [ABSTRACT FROM AUTHOR]

For integrated design of a filter and an antenna, a wideband circularly polarized (CP) dielectric resonator antenna (DRA) with filtering characteristics is proposed. A rectangular slot structure is etched on the ground to optimize the axial ratio (AR) bandwidth of the antenna singly fed by one port. Capacitive filtering branches are combined into the microstrip feeding line to effectively generate two radiation nulls outside the passband. To further enhance the suppression level in the high-frequency stopband, the stair-shaped DR is chamfered into a fish-shaped structure. A suppression level larger than 15 dB is found within the stopband. A prototype of the antenna is fabricated, and both of the simulated and measured results show a wide bandpass filtering performance over the operating frequency band. The antenna has an impedance bandwidth of 37.8%, an AR bandwidth of 25.1%, and a low profile of 0.078λ0 (λ0 is the free-space wavelength at 5.47 GHz), which can be a good candidate for 5 G and WLAN communication systems. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for the fast electromagnetic analysis of finite-sized antenna arrays (FSAAs). The conventional FSAAs are firstly deliberated as the separated elements. The characteristic modes theory (CMT) combined with the method of moments (MoM) are used to fast the simulation of each antenna element. In CMT, we extract the eigenvectors and eigenvalues of the modes. The dominant contribution of the impedance matrix is represented by the main eigenmodes in CMT. Then, the domain green's function method (DGFM) is utilized to accelerate the radiation analysis of FSAAs. The current distribution of the antenna array is calculated by eigenvalue and eigenvector from CMT of element level. The DGFMs are also improved to make it available for the unparallel array. As a result, the far-field radiation from FSAAs is evaluated quickly by the proposed DGFM-CMT. Compared with the conventional DGFM, the proposed method greatly improves the efficiency of solving radiation effects while maintains the same accuracy. Several numerical results are given to validate the proposed method. [ABSTRACT FROM AUTHOR]

A novel dual-band dual circularly polarized antenna array is proposed for vehicle satellite communication systems. The dual-band filtering element is presented, in which the dual-band characteristics are realized by vertically feeding method. The ring-shaped frequency selective configurations (RFSC) are added to the feeding network for the filtering function. The sequential rotation array is achieved by rotating four identical antenna elements around z-axis, where the phase difference of adjacent elements is 90° or −90° for the left-hand circular polarization and right-hand circular polarization, respectively. A decoupling approach is introduced to change the current paths on the surface of radiator with cutting orthogonal slots, which solves the problem of serious coupling between the different elements of the sequential rotation array. The prototype is fabricated and measured to verify the reliability of the simulations, and the simulations and measurements have reasonable consistency. The impedance bandwidths of the array are 7.26–7.46 GHz and 8.07–8.36 GHz, respectively. The port isolation of the array is greater than 30 dB in the two bands. The axial ratio (AR) bandwidths are 7.12–7.48 GHz and 8–8.36 GHz, respectively. The designed array has a promising application prospect for vehicles to satellite communications. [ABSTRACT FROM AUTHOR]

In this article, several miniaturized microstrip fifth-order lowpass filters with structure of unit artificial transmission line are presented. Reactive elements including inductors and capacitors are constructed by microstrip structures directly by parameter extraction from electromagnetic simulation. A transmission zero in stopband can be achieved by inductors and capacitors (LC) series-resonant circuit composed by parallel-plated capacitors and connecting lines. Meanwhile, loading interdigital capacitors would bring in another transmission zero. In comparison, fifth-order Butterworth and Chebyshev lowpass filters with one and two transmission zeros are fabricated, respectively, to verify the extra transmission zero effect caused by LC shunt resonant-circuits with interdigital capacitors. The proposed lowpass filters are compact and their sizes occupies less than 40% of conventional microstrip lowpass filters. The simulated and measured results demonstrate good agreements between them, which verifies feasibility of the proposed designing method. [ABSTRACT FROM AUTHOR]

A new asymmetrical Doherty power amplifier (DPA), using ferroelectric ceramics, is proposed for linearity improvement. The uneven power divider based on ferroelectric ceramics substituted for the conventional Wilkinson power divider, the uneven power divider ratio between main amplifier and peak amplifier is performed by the proposed structure, at the same time, because of the loaded ferroelectric ceramics based on Barium Strontium Titanate (BST), the phase differences between outputs of proposed divider is changed to desired by modifying the voltage of BST. Furthermore, at high power lever, the phase of peak amplifier can be modified to cancel distortion of main amplifier, so the AM-PM distortion of total DPA can be corrected by tuning voltage of BST. Compared to a conventional DPA, the third-order inter-modulation distortion of proposed DPA is reduced by 18 dB, at the same time, the PAE is also improved about 6–7%. [ABSTRACT FROM PUBLISHER]

A higher order approach for the accurate simulation of a thin dielectric sheet is proposed in this paper. Due to the small thickness of thin dielectric sheet, an equivalent surface integral equation containing tangential and normal fields can be derived from the conventional volume integral equation. Higher order bases are then applied to approximate both components. Although the programming complexity increases slightly compared with the traditional low-order thin dielectric sheet surface integral equation method, the number of unknowns required in the same problem can be drastically reduced in the proposed higher order approach. At the same time, a higher accuracy can be achieved. Numerical results are presented to show the high efficiency and stability of the proposed method. [ABSTRACT FROM PUBLISHER]

A novel scheme of an electrically tunable microstrip patch antenna using an electroactive polymer Poly(vinylidene fluoride-trifluoroethylene) thin film as a part of substrate is presented. The suited plus DC power supply is produced and applied to adjust the permittivity of the Poly(vinylidene fluoride-trifluoroethylene) film, which is imposed directly on the copper patch of the antenna. The patch is designed to be the same size as the ground plane to guarantee the plus static electric field inside the film uniformly. With the proposed structure, an electrical frequency agile microstrip patch antenna that performs well is achieved. The measured results demonstrate that the resonant frequency can be unceasingly tuned from 3.72 to 4.025 GHz; when the DC voltage changed from 0 to 430 V, a frequency tuning range of 7.57% is obtained. [ABSTRACT FROM AUTHOR]

A novel wideband dual-polarized printed dipole antenna fed by two integrated feeding networks is presented. The feeding network, a kind of compact halfwave balun, delivers equal amplitude (within 0.1 dB) and 180° (±5°) phase difference between the two output ports from 1.65 to 2.8 GHz. By employing an H-shaped slot in each arm of the dipole, wide impedance bandwidth has been obtained. Experimental results show that the proposed antenna can operate from 1.7 to 2.7 GHz with low voltage standing wave ratios (<1.5) at the two ports. Low cross-polarization (>25 dB) and high isolation (>31 dB) are also achieved over the entire bandwidth. Moreover, stable radiation patterns and low back lobes are obtained by using a modified reflector. [ABSTRACT FROM PUBLISHER]

In this article, a new numerical approach to calculate the retarded-time scalar and vector potentials is proposed that resulted from the impulsive basis on curvilinear quadrilateral patches. This approach employs a numerical method to get the arc segment, which is the intersection of the curvilinear quadrilateral patch and the sphere centered at the observation point. The radius of sphere varies with the time. Then the retarded-time potentials are obtained by the volume integral on those curves. The validity of this method is verified by comparing results from the proposed method with those obtained through inverse Fourier transform of frequency-domain results. [ABSTRACT FROM PUBLISHER]

The higher-order maximal orthogonal vector basis functions are used to get a target's sampling information in interpolation/extrapolation of electromagnetic responses in the time and frequency domains. With the method, the computational complexity of sampling would decrease sharply without loss of accuracy. As a result, the proposed method solved the problem of high computational complexity and great resource consuming of a traditional sampling method. Some numerical results are given to verify the high efficiency and accuracy of this method. [ABSTRACT FROM AUTHOR]

The higher-order hierarchical vector basis functions can be used to reduce the number of unknowns significantly. They can be easily applied in electromagnetic and geometrical modeling due to the fact that they are defined on the quadrilateral patches and do not need the conform patches. In this article, the higher-order hierarchical vector basis functions were used to compute the time-domain scattering of perfect electric conductor objects. Specifically, the basis functions are implemented to solve the time-domain integral equation with the Galerkin method and the point matching for spatial and time-domain discretization, respectively. Moreover, the implicit matching on-in time method is used in this article. Simulation results are presented to demonstrate the high accuracy, efficiency, and stability of the proposed method. [ABSTRACT FROM AUTHOR]