A double-layer frequency selective surface (FSS) with dual rings is used as a reflector in the design of an Archimedean spiral antenna (ASA) with low radar cross section (RCS) and uni-directional characteristics. The proposed FSS presents a stopband in the range of 2 GHz to 4.7 GHz, which is applied to ASA to form a unidirectional radiation pattern with front to back ratio (FBR) values larger than 10 dB in the stopband, and the maximum FBR value is up to 25.26 dB. Compared with the reference antenna with the same-size metallic ground, the proposed FSS reduces the RCS about 2.5-38 dB in the frequency ranges of 4.8-30 GHz. And the FSS antenna also exhibits better axial ratio characteristics in the frequency range of 2.8-8.1 GHz. The composite structure is compact, with a total height of 0.18 wavelength at the lowest analysis frequency of 2 GHz. Measured results indicate that the proposed antenna reproduces the inherent wideband of the original ASA from 1.6 GHz to 8.1 GHz. Meanwhile, the gain of the ASA is increased by 3 dBi. Full-wave simulations and measurements prove that the novel FSS reflector can be employed to replace a metallic ground which realises a uni-directional ASA with broadband low RCS, high gain and good circular polarization (CP) performance.
In order to reduce the cost and blindness of antenna design, the application of electromagnetic field similarity principle in the working environment of underwater receiving antenna was studied and verified. The field distribution and electrical parameters of the underwater receiving antenna and its reduced-scale model were calculated and proved to be in accordance with the similarity principle. The simulation analysis of the receiving antenna and its reduced-scale model for receiving the airborne electromagnetic wave signal in the seawater shows that the underwater receiving antennas before and after the scale-down are similar. The simulation is verified by measuring the receiving signal amplitude of the underwater receiving antenna and its reduced-scale model. The results of theoretical derivation and simulation analysis show that the electromagnetic field similarity principle can be applied to the underwater receiving antenna system.
In this paper, two different architectures based on fully and partially clustered arrays are proposed to optimize the array patterns. In the fully clustered arrays, all the elements of the original array were divided into several equal subarrays, while in the partially clustered arrays, only the side elements were grouped into subarrays, and the central elements were left individually. The second architecture enjoys many advantages compared to the first one. The proposed clustered arrays use quantized amplitude distributions, thus, their corresponding patterns were associated with high side lobes. To overcome this problem, a constraint mask was included in the pattern optimization process. Simulation results show that the peak sidelobe level and the complexity of the feeding network in the partially clustered arrays can be reduced to more than -28 dB and 70.833% respectively, for a total of 48 array elements, number of individual central elements = 24, number of clusters on both sides of the array Q = 4, and number of elements in each side cluster M=6. Finally, the principles of the proposed clustered arrays were extended and applied to the two dimensional planar arrays.
In this paper, a planar, compact, and low cost printed microstrip line fed pentagon-shaped ultra-wideband antenna offering dual band notched characteristics response is proposed and investigated. By introducing modified V-shaped slots in the pentagonal patch and hexagonal electromagnetic band gap structures near the feedline, dual band notched response can be realized. The proposed antenna is successfully simulated, designed, and fabricated on an FR-4 substrate. The measured results show that the proposed antenna having dimensions of 35 × 33 × 1.6 mm3 has a bandwidth over the frequency band 2.7-10.6 GHz with magnitude of S11 ≤ -10 dB (VSWR ≤ 2), except 3.7-4.6 GHz (C-band Satellite Communication) and 5.16-6.08 GHz (WLAN) frequency bands. The presented antennas show small group delay variation, nearly omnidirectional radiation pattern and stable gain at working frequencies. Satisfactory results have been obtained in frequency and time-domain analysis of the proposed antenna. The formulation of the center frequency of dual notched frequency band is also proposed.
In this paper, a novel single-layer anisotropic unit with both reflection and transmission functions is proposed. The unit is a ring-encircled two mirror-symmetry fan-shaped patches, and is fabricated in one side of an F4B substrate. The unit structure is asymmetry with respect to x- and y-axes, and both transmitted and reflected cross-polarized fields are generated simultaneously when the co-polarized field is incident on the symmetry broken surface. Full 360° phase shift range is achieved by utilizing the cross-polarized field, and the transmitted and reflected coefficient magnitudes are above 0.49 close to the theoretical limit. Using this anisotropic unit, three single-layer transmit-reflect-arrays are designed: (1) Two high-gain beams in (θ1 = 0°, φ1 = 0°) and (θ1 = 180°, φ1 = 0°) directions. The gain is 20.9 dBi, and the 3 dB beam width is 8.9°. (2) Two OAM beams with l = 1 at (θ1 = 45°, φ1 = 0°) and (θ2 = 135°, φ2 = 0°). (3) Four OAM beams with l = 1 at (θ1 = 30°, φ1 = 0°), (θ2 = -30°, φ2 = 180°), (θ3 = 150°, φ3 = 0°) and (θ4 = -150°, φ4 = 180°). The simulated and measured results agree well and validate the design principle. The proposed metasurface has the following advantages: single-layer, transmission and reflection dual-functions, multi-beam, and high gain.
To diminish electromagnetic interference (EMI) for microwave radiations, effects of graphite (Gr) modified by a long alkyl chain ionic liquid (IL) 1-Butyl-3-methylimidazolium hydrogen sulphate ([BMIM][HSO4]) on poly(vinylidene fluoride) (PVDF), was investigated. The pre-localized Gr coated polymer powders were fabricated, using solvent blending method, with different concentrations of Gr over PVDF matrix to prepare a series of PVDF/Gr/IL composites. The surface morphology of the fabricated composite films was examined by scanning electron microscopy (SEM). The composites, with a thickness of ~0.15 mm, exhibit good EMI shielding properties, besides low cost production and flexibility. The enhanced properties are due to high ionic conductivity of the IL and formation of a connecting network by Gr facilitating electron conduction. Absorption is the key factor due to which the total shielding effectiveness in the frequency band of 12 to 18 GHz has been improved significantly.
In this paper, a flexible metamaterial-based electromagnetic harvester is proposed for wearable applications at microwave regime. The proposed harvesting structure is composed of a modified configuration from the conventional Split-Ring Resonator (SRR) inclusion and is printed on a grounded very thin flexible substrate. The proposed wearable harvester structure provides several interesting features, including its robustness, sustainability and ease of integration with flexible electronics and sensors. Numerical full-wave studies are conducted, where results from a periodic arrangement of the proposed harvesting unit cell along with several two-dimensional arrays of harvesters are presented and discussed. Based on the numerical studies, the proposed electromagnetic harvesting structure exhibits good efficiency capability of power conversion from radio frequency received power to alternating-current harvested power across collecting loads above 90% for the three studied cases.
In this paper, a planar inline fully-canonical topology is proposed to reduce sensitivity to fabrication tolerances compared to conventional inline all-pole configurations. Major concerns are related with errors in the absolute positioning of via-holes to ground which affect inter-resonator (main-line) couplings. The total expanded sensitivity considering variations of the main-line couplings have been obtained for fully and non-fully canonical configurations. The result shows that sensitivity is lower in the case of fully-canonical topologies. Moreover, the allocation of the transmission zeros plays a key role in terms of sensitivity. A prototype has been designed for the Ku-band based on asymmetrical coupled lines obtaining IL=-1.6 dB, RL below -18 dB, and out-of-band rejection higher than -50 dB.
This paper presents a highly innovative approach of amplitude steering without the use of variable gain amplifiers (VGA). This approach involves the use of a Reconfigurable Ratio Power Divider (RRPD), and does not suffer from the instability, poor efficiency, and worsened SNR associated with the use of VGAs. The RRPD, which is reconfigured manually by means of a potentiometer, is used to feed a 2 x 1 antenna array. By varying the power dividing ratio of the RRPD, continuous beam steering is achieved through passive amplitude control. The antenna was designed to operate at 2.4 GHz and had a continuous steering range from 0° to 21° while maintaining a stable return loss around the centre frequency. An expression that relates the reconfigurable ratio to the variable resistance was derived empirically. The prototype amplitude steerable antenna was fabricated and measured to validate the analyses.
In this paper, a novel branch line coupler with improved bandwidth and reduced size is presented. The size reduction is achieved by means of capacitive loading. The capacitive loaded transmission line implemented in the proposed design eliminates the need of open stubs. The mechanism of size reduction and bandwidth enhancement of the coupler is discussed analytically with the help of its equivalent circuit. A prototype is fabricated and tested to validate the concept. The measured fractional bandwidth is 40%, ranging from 2.8 GHz to 4.2 GHz which is suitable for 5G systems. Moreover, the obtained phase imbalance between the output ports is less than ±5° for the entire operating range.
Here we propose an L-shaped slot-type MIMO antenna with pattern and circular polarization diversity for WLAN applications. In order to maintain a low profile, the pattern and polarization diversities have been achieved without using additional supporting structures. Both the antenna elements are located at the corners of the same side of the ground plane. One of the antenna elements produces left hand circularly polarized (CP) waves whereas the other element produces right hand CP waves in (front) +z-direction. The senses of polarizations are opposite in (backward) -z-direction. CP waves have been generated using two orthogonal current modes, excited by locating the slots on the corner of the ground plane. The quadrature phase difference between the modes has been employed using the slot geometry. In other directions, the antenna correlation has been reduced using pattern diversity. The measured results confirm the simulated ones. The measured axial ratio bandwidth (< 3 dB) and the matching bandwidth (< -6 dB) are 380 MHz and 110 MHz, respectively. The envelop correlation coefficient is less than 0.1 in the operating band.
A compound or an offset inclined slot fed by a rectangular waveguide has been analysed using the image method for the evaluation of internal admittance in the Method of Moments framework. The internal admittance has been evaluated from the 2D infinite planar array equivalent image representation of a slot in a waveguide. The advantages offered by this method include the freedom to work in slot coordinates rather than the waveguide coordinates, the reuse of external admittance for air filled waveguides, and the flexibility in the choice of the mutual admittance evaluation technique. Unlike the conventional mode method, the proposed technique does not run into difficulties while evaluating the fields from longitudinal magnetic current for points in the same transverse plane. The θ-algorithm has been used for the convergence acceleration of the series of mutual admittances in the internal admittance evaluation and has been shown to yield better results than other convergence acceleration algorithms investigated. The results obtained from this method have been shown to agree within 0.5% average with those from other theoretical techniques and within 1% average with measurements. The proposed method is useful in the design of compound slot arrays and can be extended to other configurations where the image representation is possible and for various slot aperture distributions.
The coil stray capacitance is an essential factor for high-frequency coil application, such as wireless power transfer system. In this paper, in order to calculate the planar coil stray capacitance at Megahertz frequency, the theory model has been built. Based on the basic capacitance calculation equation, the mathematical model has been deduced carefully. Then, the mathematical model has been evaluated by a series of simulation models. In the simulation part, the error of the variables of the theory model has been analyzed carefully and quantitatively. In order to verify the theory and simulation model, the verification experiment has been done. The experimental results are consistent with the simulated ones and the theory model. The experimental and simulated results indicate that the theory model of the coil stray capacitance has a satisfactory accuracy, and the model has application potential in the field of wireless power transfer.
In this paper, we propose a new methodology to design an electromagnetic invisibility anti-cloak, which is based on nonlinear coordinate transformation. Cylindrical and elliptical shapes are presented to show the validation of the proposed methodology. We verify and analyze the above model with nonlinear transformation respectively. Full-wave simulations are given to illustrate the ability of the nonlinear transformation, which is advantageous for reducing the design difficulty of the anti-cloak. And the cloak shielding is broken, and the electromagnetic waves can go through the cloak. It is of particular importance in microwave communication applications.
We derive and verify a new type of low-complexity neural networks using the recently introduced spatial singularity expansion method (S-SEM). The neural network consists of a single layer (Shallow Learning approach to machine learning) but with its activation function replaced by specialized S-SEM radiation mode functions derived by electromagnetic theory. The proposed neural network can be trained by measured near- or far-field data, e.g., RCS, probe-measured fields, array manifold samples, in order to reproduce the unknown source current on the radiating structure. We apply the method to wire structures and show that the various spatial resonances of the radiating current can be very efficiently predicted by the S-SEM-based neural network. Convergence results are compared with Genetic Algorithms and are found to be considerably superior in speed and accuracy.
This paper presents the work of the LAPLACE Electromagnetism Research Group to build an experimental setup able to measure tiny forces that may appear in microwave cavities, in the context of EMDrive investigations. It is based on a commercial balance in the range of 0.1 mN sensitivity, a contactless feeding for more than 150~W RF power, and self calibrating device process. It requires a double cavity system in mirror configuration and is here experimented with frustum cavities, different from the NASA one . The global setup can make force measurement and calibration in less than two seconds. Investigating two different cavities and various electromagnetic modes for the biggest, no force is reported while the 0.1 mN sensitivity is demonstrated.
Electric dipoles are the fundamental components of a planar multi-layered circuit. Present work focuses on the theoretical investigations of radiation field due to a vertical electric dipole in a four-layered region composed of a perfect conductor covered with two dielectrics and the air above. Locating a vertical electric dipole (VED) on or near the air-dielectric boundary, approximate formulas are obtained. The resultant analytical formulas have the merit of offering unique insights about the characteristics of the radiation field including direct waves, reflect waves, lateral waves, and trapped surface waves. The amplitude of the field along the boundary exhibits the dependence of ρ-1/2, which is an intrinsic characteristic of trapped surface waves, where ρ is the propagation distance. In addition, the radiation field is further examined for propagation distance and propagation characteristics of the interference phenomenon. Furthermore, when the observation angle Θ ≥ 88°, the lateral wave still exists; however, the trapped surface wave is a major component of the total field. The proposed formulas have potential to develop planar four-layered circuit structures.
In this paper, we focus on the energy efficiency (EE) optimization for an amplify-and-forward (AF) relay network, where the energy-constrained relay harvests energy from a transmitter using power splitting (PS) scheme. We aim to maximize the EE of the network via jointly optimizing the transmit precoding, relay beamforming, and PS ratio, under the constraints of transmit power and the spectral efficiency. To solve the formulated fractional programming, we approximate the problem via two layer optimization, where the outer problem is handled by the Dinkelbach method, and the inner problem is solved by penalized difference-of-convex (DC) and constrained concave-convex procedure (CCCP). Finally, an iterative method is proposed. Simulation results demonstrate the performance of the proposed design.
This research work adopts an open-circuited-series stub-tuning in sequence with unmatched antenna radiator to bring out a small form factor. Thereby, the effective antenna radiator size has been shrunk up to 0.2λ, where similar efficiency and beam pattern has been maintained. The antenna is conceptualized with symmetrical slots, which indicates a multi-ring structure to contribute multiband miniaturization. This consists a loop based rectangular-ring connected with an E-shaped patch, which is excited through a microstrip stepper impedance transmission line followed by an equally distributed strip-line. It enables enhanced impedance-matching at 2.76 GHz and 6.34 GHz by a stepper impedance transmission line with stub-loading technique. The antenna aperture area miniaturization of 56% has been achieved by introducing slots on the radiator patch. Moreover, this miniaturized patch exhibits improved gain response of 4.43 dBi and 5.37 dBi in the broadside direction. The proposed design occupies a dimension of (0.22λ × 0.26λ) mm2.
A problem of electromagnetic wave radiation by narrow slots cut in an end wall of a semi-infinite waveguide section into space above a perfectly conducting sphere is solved in a strict self-consistent formulation by the generalized method of induced magnetomotive forces (MMF). Inside the waveguide section, a reentrant cavity formed by the volume between a slotted diaphragm and the waveguide end wall is located. The waveguide is operating in the frequency range of a single-mode regime. The electrodynamic characteristics of this radiating system with the spherical screen of resonant dimensions are investigated numerically and ex-perimentally. The possibility to develop the spherical antennas with a narrow-band frequency, energy, and spatial characteristics is substantiated.