A novel transmitarray element consisting of only two layers of modified Malta crosses printed on a dielectric substrate is proposed, and vias are employed to augment the transmission magnitude and ...enhance its phase shift range. A prototype transmitarray with a circular aperture of 338 mm in diameter is then designed, fabricated, and tested to validate the proposed design. The simulation and measurement results show good radiation characteristics with measured gain of 33.0 dBi at 20 GHz and aperture efficiency of 40%. The proposed element considerably simplifies the complexity of a transmitarray, reducing its thickness, mass, and cost.
A high-efficiency wideband frequency selective surface (FSS)-backed 20/30-GHz dual-band circularly polarized reflectarray antenna is presented. In order to effectively suppress the mutual coupling ...between the different element sets and improve the aperture efficiency, the variable element size and the element rotation angle phasing techniques are utilized in the multilayer reflectarray element designs at the Ka receive and transmit bands, respectively. Furthermore, a double-layer FSS with double concentric square loops is employed between the 20- and 30-GHz element layers. Thus, the uncoupled 20/30-GHz phase responses can significantly reduce the phase errors and simplify the dual-band reflectarray design process. To experimentally validate the performance of the proposed FSS-backed element configuration, an offset-fed 20/30-GHz dual-band circularly polarized reflectarray with a circular aperture of 400 mm is designed, fabricated, and measured. The measured gains are 36.7 dBic with aperture efficiency of 64.1% at 20.4 GHz and 40.2 dBic with aperture efficiency of 65.4% at 30.2 GHz, respectively. The measured aperture efficiencies exceed 47% within the whole receiving band (19.6-21.2 GHz) and 59% within the whole transmitting band (29.4-31 GHz), respectively. The proposed dual-band circularly polarized reflectarray antenna can be used for satellite communication applications at Ka-band.
A dual-frequency reconfigurable reflectarray (RRA) is proposed and verified experimentally. The RRA consists of 1600 electronically controllable elements. By integrating only a single PIN diode, the ...proposed element is capable to operate at two working frequencies with 1-bit phase resolution. The dual-frequency mechanism is explained through the mode analysis, and a parametric study is performed to provide guidelines for determining the two working frequencies. As an example, a 1600-element RRA prototype is realized by assembling five identical 8 x 40 subarrays. An field programmable gate array control board is used to achieve real-time phase control of each element individually. The experimental results show that the broadside gains of the RRA are 29.3 and 30.8 dBi at 11.1 and 14.3 GHz, respectively. Excellent beam scanning performance is also obtained at both frequencies.
A single-layer dual-band circularly polarized reflectarray antenna has been designed, fabricated, and tested for Ka-band satellite communications. The reflectarray antenna phasing element is composed ...of a concentric split-ring, in combination with a modified Malta Cross, where the technique of varying rotation angle and element size has been utilized to compensate the phase delay at 20 and 30 GHz, respectively. All the element configurations have been optimized to reduce cross-polar reflection. The aperture field method has been used to predict the reflectarray radiation performance, such as gain, radiation pattern, and cross-polarization level. A reflectarray with a circular aperture of 420 mm in diameter has been designed, manufactured, and tested for verification. A planar near-field measurement setup has been utilized to measure the reflectarray radiation characteristics. The measured results demonstrate that this dual-band reflectarray has achieved aperture efficiency of 66.5% at 20 GHz and 50% at 30 GHz, respectively.
One of the key enablers of future wireless communications is constituted by massive multiple-input multiple-output (MIMO) systems, which can improve the spectral efficiency by orders of magnitude. In ...existing massive MIMO systems, however, conventional phased arrays are used for beamforming. This method results in excessive power consumption and high hardware costs. Recently, reconfigurable intelligent surface (RIS) has been considered as one of the revolutionary technologies to enable energy-efficient and smart wireless communications, which is a two-dimensional structure with a large number of passive elements. In this paper, we develop a new type of high-gain yet low-cost RIS that bears 256 elements. The proposed RIS combines the functions of phase shift and radiation together on an electromagnetic surface, where positive intrinsic-negative (PIN) diodes are used to realize 2-bit phase shifting for beamforming. This radical design forms the basis for the world's first wireless communication prototype using RIS having 256 two-bit elements. The prototype consists of modular hardware and flexible software that encompass the following: the hosts for parameter setting and data exchange, the universal software radio peripherals (USRPs) for baseband and radio frequency (RF) signal processing, as well as the RIS for signal transmission and reception. Our performance evaluation confirms the feasibility and efficiency of RISs in wireless communications. We show that, at 2.3 GHz, the proposed RIS can achieve a 21.7 dBi antenna gain. At the millimeter wave (mmWave) frequency, that is, 28.5 GHz, it attains a 19.1 dBi antenna gain. Furthermore, it has been shown that the RIS-based wireless communication prototype developed is capable of significantly reducing the power consumption.
Design of a circularly polarized reconfigurable reflectarray antenna (RRA) at X band is presented. The RRA element employs concentric dual split rings, and can be mechanically rotated to obtain ...continuous 360° phase coverage with negligible element loss. A prototype with 15 × 15 manually rotated elements is first computed, simulated, and measured. Full-wave simulations show that the gain of the beam focused in (8 = 20°, φ = 0°) direction is 25.8 dB and the 1-dB gain bandwidth is over 28.6%. The measured results show that the beam at (8 = 20°, φ = 0°) direction achieves the maximum gain of 25.6 dB, corresponding to an aperture efficiency of 51.8%. The beam-steering capability of the RRA is measured within ±60° angular range, and well-defined scanned beams are obtained with maximum scan loss of 3.7 dB. The versatile beam-forming capability of the RRA is also verified by synthesizing a square shaped beam and a cosecant shaped beam. Another micromotor-controlled prototype with 756 elements on an octagonal aperture is fabricated and its measured radiation performance validates the feasibility of the proposed design as well.
This communication proposes a novel wideband phase synthesis approach, which is able to considerably increase the bandwidth of the reflectarray antenna independent of the element frequency behavior. ...Specifically, the reference phases at the Ku-band transmitting and receiving frequencies are optimized, simultaneously, to minimize the total phase error of the reflectarray. Simulation and experimental results of reflect-arrays consisting of simple square-ring elements show that a 16.7% measured bandwidth within 1.5-dB gain variation can be achieved by a single-layer design with a thin substrate. The proposed approach is applicable to general reflectarray elements and the phase synthesis process is easy-to-implement compared with other conventional wideband reflectarray designs.
A dual-band transmitarray is proposed for downlink/uplink frequencies (12.5/14.25 GHz) of Ku-band satellite communications. The basic building block for the dual-band transmitarray is a three-dipole ...element. Such two elements are interlaced in orthogonal polarization for each frequency band independently. This element overwhelms the basic phase restriction of a simple dipole element, and 360° phase range can be achieved in both bands with a four-layer configuration. However, it is explored (theoretically and experimentally) that three layers are preferred to be used instead of four layers due to a compromise between the phase range and reflection loss. A high-gain three-layer dual-band orthogonally polarized transmitarray is designed successfully. The measured results match well with simulation results, and high gains of 31.0 and 31.8 dBi are achieved with aperture efficiencies of 45.0% and 41.3% at 12.5 and 14.25 GHz, respectively. It also achieves 1 dB gain bandwidths of 7.2% and 7.0% in both the downlink and uplink frequency bands, respectively.
A novel design methodology for single-layer dual-band reflectarray antennas with wide frequency ratios is proposed by exploiting the unique reflection phase properties of Phoenix elements. Full 360° ...phase ranges at both frequency bands are achieved simultaneously by using only one element set. Compared to conventional approaches that use two sets of elements for dual-band operation, physical and electromagnetic mutual interferences between the elements operating at different frequency bands can be completely avoided. A detailed design procedure for single-layer dual-band reflectarrays with a wide frequency ratio up to 2.5 is presented, and a set of three center-fed dual-band reflectarrays operating at 15/10, 20/10, and 25/10 GHz, respectively, are designed and numerically verified using full-wave simulations. Furthermore, an offset-fed single-layer dual-band reflectarray operating at 20/10 GHz with a circular aperture of 400 mm in diameter is designed, fabricated, and tested for experimental verification. The measured gains are 36.1 dBi with an aperture efficiency of 58.0% at 20 GHz and 30.3 dBi with an aperture efficiency of 61.1% at 10 GHz, respectively. The measured 1-dB gain bandwidth is 9.1% and 14.0% at the upper and lower bands, respectively. Both the simulated and measured results successfully demonstrate the effectiveness of the proposed design methodology.
Fast and efficient computational electromagnetic simulation is a long-standing challenge. In this article, we propose a data-driven model to solve Poisson's equation that leverages the learning ...capacity of deep learning techniques. A deep convolutional neural network (ConvNet) is trained to predict the electric potential with different excitations and permittivity distribution in 2-D and 3-D models. With a careful design of cost function and proper training data generated from finite-difference solvers, the proposed network enables a reliable simulation with significant speedup and fairly good accuracy. Numerical experiments show that the same ConvNet architecture is effective for both 2-D and 3-D models, and the average relative prediction error of the proposed ConvNet model is less than 3% in both 2-D and 3-D simulations with a significant reduction in computation time compared to the finite-difference solver. This article shows that deep neural networks have a good learning capacity for numerical simulations. This could help us to build some fast solvers for some computational electromagnetic problems.
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