A planar endfire circularly polarized quasi-Yagi antenna with the feasibility of obtaining a wider bandwidth and relatively smaller size is proposed and demonstrated. With a planar double-sided printed complementary structure, the proposed endfire circularly polarized (CP) antenna, consisting of a vertically polarized planar quasi-Yagi array and a horizontally polarized planar quasi-Yagi array with a common driver, is designed, analyzed, and fabricated. Good agreement between simulated and measured results is observed. Simulation and measurement results reveal that the proposed antenna can provide an impedance bandwidth of 16.3% (5.02-5.91 GHz) and a 3 dB axial ratio (AR) bandwidth of 17.4% (5-5.95 GHz). Meanwhile, the proposed antenna has endfire gains from 5.4 dBic to 7.4 dBic with an average endfire gain of 6.3 dBic, and front-to-back (F/B) ratios ranging from 10.2 dB to 16 dB with an average F/B ratio of 11.9 dB. Additionally, the measured effective CP bandwidth of 16.3% (5.02-5.91 GHz) not only meets the need for certain Wi-Fi (5.2/5.8 GHz) or WiMAX (5.5 GHz) band communication application, but also provides the potential to implement multiservice transmission.
The design guidelines have been proposed for achieving efficient wireless Electric Vehicle (EV) charging system under non-ideal practical scenarios. The effects of operating parameters have been investigated by addressing the fundamental hurdle to the widespread usage of magnetic resonance coupling (MRC) based wireless EV charging system. From both experimental and simulated results, it has been perceived that the power transfer efficiency (PTE) depreciates rapidly as the charging condition deviates from the ideal one. It is observed that PTE can be managed to enhance from the deteriorated value to an acceptable level through proper consideration of separation air gap of the charging coils, frequency of operation with acceptable horizontal offsets, suitable coil models, position of metallic object and coil properties. To maintain the maximum PTE even under non-ideal scenario, an automated frequency tuning method has also been delineated. The corroborated experimental and simulated results can provide a complete strategic plan in the design of an efficient practical wireless power transfer system to be utilized for EV charging system.
The context of the paper is the 50-60 Hz electromagnetic interference between AC power lines/electrified railway lines and pipelines; we present here an algorithm for the evaluation of the AC induced current density, flowing through the holidays (defects) in the pipeline insulating coating, from pipe to soil by modelling this last one as a two-layer structure. Moreover, the value of holidays area is treated as a random variable (as actually is from field experience) so allowing to associate a certain level of probability to the event of exceeding the AC current density limit, established by standards, for AC corrosion risk. The results show that the surface layer soil resistivity is a very significant factor influencing the level of AC induced current density.
We engineer very low aspect ratio Aluminum (Al) based periodic plasmonic nanostructures with period ≈ resonance wavelength for enhanced refractive index and thickness sensing, which offer to access complete ultraviolet-visible-near infrared spectral range for SPR sensors. Al-based periodic nanostructures on top of a thin homogeneous Al metal coated on a BK-7 glass substrate were designed by systematic variation of geometrical parameters using Rigorous Coupled Wave Analysis and finite elements full wave solver, while, taking into account applicable fabrication constraints. The reason of adding a thin layer of homogeneous Al metal between the nanostructure and glass substrate was to convert the signature of Surface Plasmons (SPs) from transmission dips to transmission peaks, using ±1st order diffraction mode. The shift in SP mode excited on the nanostructure-analyte interface was used to measure the variation in refractive index, and the number of waveguide modes with the increase in the thickness of the analyte was used to capture the variation in thickness of the analyte. The proposed nanostructures of period 400 nm and an aspect ratio of 0.1 offered a sensitivity of 400 nm/RIU and full width at half maximum of 18 nm resulting in a figure of merit of 22. These plasmonic nanostructures have potential to be used as refractive index and thickness sensor due to a high figure of merit, high localization of the field, and very low aspect ratio that is needed to maintain laminar flow of analyte.
Global Navigation Satellite System Reflectometry (GNSSR) can be used to derive information about the composition or the properties of ground surfaces, by analyzing signals emitted by GNSS satellites and reflected from the ground. If the received power is measured with linearly polarized antennas, under the condition of smooth surface, the reflected signal is proportional to the modulus of the perpendicular and parallel polarization Fresnel coefficients, which depend on the incidence angle θ, and on the dielectric constant ε of the soil. In general, ε is a complex number; for non-dispersive soils, the imaginary part of ε can be neglected, and a real value of ε is sought. We solve the real-valued problem explicitly giving formulas that can be used to determine the dielectric constant ε and we compare the analytical solution with experimental data in the case of sand soil.
A compact slot-coupled endfire radiation antenna based on a tapering spoof surface plasmon polaritons (SSPPs) structure with high efficiency is proposed in this paper. A narrow slot balun is designed to feed the SSPPs structure rather than to work as the primary radiator. Simulated results show that the odd SPP mode is successfully excited on the tapering SSPPs structure, which contributes to the endfire radiation. Due to the high confinement of SSPPs, the proposed antenna shows low RCS within the frequency band of 1.5 GHz-4 GHz and 5.6 GHz-8 GHz. A prototype is fabricated and tested. Simulated and measured results show good agreement that the proposed antenna can provide stable endfire radiation patterns within the frequency band of 2 GHz-3.4 GHz. The maximum gain reaches 8 dBi, and the average efficiency over this bandwidth is 80%. The high-efficiency endfire SSPPs antenna with balanced broad band and high gain has a promising application in communication systems and integrated circuits.
In this paper, we systematically derive design equations for 3-way Bagley power dividers with arbitrary split ratios using interconnecting transmission lines with the same characteristic impedance. The exact value of the characteristic impedance for a specific dividing ratio is determined using these equations to achieve perfect input port matching. To validate the design procedure, two microstrip dividers with different split ratios, 1:3:1 and 1:10:1, are designed, simulated, fabricated, and measured. The desired split ratios are achieved at the design frequency, 1 GHz. Good agreement between simulated and measured results is obtained.
Magnetic coupling resonance wireless power transfer (MCR-WPT) technology has been in development for over a decade. The output power of the MCR-WPT system achieves the maximum value at two splitting frequencies and not at the natural resonant frequency because frequency splitting occurs in the over-coupled region. In order to achieve excellent transfer characteristics, optimization approaches have been used in many MCR-WPT projects. However, it remains a challenge to obtain a constant output power in a fixed-frequency mode. In this research, two receiving coils are used in the MCR-WPT system to achieve a uniform magnetic field. First, a circuit model of the MCR-WPT system is established, and transfer characteristics of the system are investigated by applying the circuit theory. Second, the use of two receiving coils to achieve a uniform magnetic field is investigated. Constant output power is then achieved in a fixed-frequency mode. Lastly, the experimental circuit of the MCR-WPT system is designed. The experimental results are consistent with the theoretical ones. The topology of using two receiving coils results in optimum transmission performance. Constant output power and high transfer efficiency are achieved in the higher frequency mode. If the distance between the two receiving coils is appropriate and the transmitting coil moves between the two receiving coils, the fluctuation of the output power of the MCR-WPT system is less than 10%.
Chipless RFID with small, printed metal tags have been proposed as a cost-effective alternative to chip-based technologies. A potentially viable configuration is to image the patches of different shapes, sizes, and orientations within a tag with a tabletop-scale synthetic aperture radar (SAR), operating in the V or W band. Information is encoded into, e.g. polarization, resonance characteristics, and phase of the scattered signal. The effect of electromagnetic coupling and sidelobe interference between closely spaced metal patches on SAR image has not been addressed in prior studies. To be specific, we analyze 60 GHz circular SAR (CSAR) imagery of subwavelength patches separated by distances on the order of wavelength. The scattered field is calculated with the method of moments (MoM) to account for EM interaction. The field is then used to form CSAR image with the polar formatting algorithm (PFA). Significant distortion of the CSAR image is found at this scale. Sidelobe interference causes image distortion and up to 7 dB of intensity modulation with patch separation. EM coupling produces an ``interaction image,'' an artifact that extends between the patches. The source of this effect is traced to induced currents and charges residing on the patches' inner edges. Increasing system bandwidth or changing the incidence angle has minimal effect on both classes of image artifacts, highlighting the importance of accounting for them in practical system design and subsequent information processing.
Recent studies show that the frequency dependent soil properties can significantly influence transient grounding resistance and, subsequently, lightning protection and reliability of the electrical grid. However, these properties require further research: for example, it is not clear what factors (apart from the low-frequency resistivity) should be taken into consideration to determine accurately the properties for a particular soil (without conducting laborious measurements). Additional experimental data are needed. When measurements are conducted, the electromagnetic coupling between circuits can cause significant measurement error at frequencies about several MHz. In order to estimate this error, it is convenient to use a calculation method, as in this case, it is possible to set particular frequency dependent properties for the ground and compare those with the calculated ones (using an electrode array). In the article, the electromagnetic coupling error is examined for several commonly used electrode arrays using the finite difference time domain method. This method allows simulating wires with in nite length, which is important for modeling pole-dipole and pole-pole arrays. Its drawback for this type of calculations, however, that it is relatively time-consuming. It was found that among the considered array configurations the error is smallest for the dipole-dipole arrays with the perpendicular allocation of the measurement wires and the pole-dipole array. By increasing the distance between particular parts of measurement wires, one can significantly reduce the error for some other arrays.
Most of space-time adaptive processing methods have the excellent ability to suppress interferences when the space-time covariance matrix is perfectly estimated. Unfortunately, these methods may have calculation error of the covariance matrix in the case of fewer snapshots, which may lead to remarkable performance degrading. To solve the aforementioned problem, a space-frequency domain anti-jamming algorithm based on the compressed sensing theory (CS-SFD) is presented. Firstly, the proposed method utilizes less sampled data to form a space-frequency two-dimensional sparse representation for the narrowband interference signals. Secondly, the interference covariance matrix estimation problem is modeled as a sparse reconstruction problem which can be efficiently solved by the orthogonal matching pursuit algorithm. Furthermore, the diagonal loading method is used to modify the interference plus noise covariance matrix. Finally, the weight vector is given by the minimum output power criterion. Compared with the previous work, the presented method has better robustness and more effectively anti-jamming performance in the case of fewer snapshots. Simulation results show the effectiveness of the proposed algorithm.
Aiming at the problem of high false alarm rate with respect to adaptive threshold in the ship detection from synthetic aperture radar (SAR) images, a novel strategy increasing robustness when using local adaptive threshold is proposed. In this article, we establish a fusion detection model based on a combination of the information geometry and surface geometry. Information geometry from a metric viewpoint can increase the contrast between targets and clutter in SAR image. Local surface feature gives a brief application of adaptive threshold method in ship detection from SAR images by means of the constant false-alarm-rate. Experiments indicate that the proposed geometry-based approach can effectively detect ship targets from complex background SAR images by using the method of fusion processing.
Body gesture recognition can be applied not only to social security but also to rescue operations. In reality, body gesture can produce unique micro-Doppler signatures (MDSs), which can be used for identification. In this paper, we first acquired the echo signals of four body gestures via a Ka-band dual polarization radar system under different angles and distances. The four gestures are respectively swinging arm up and down, swinging arm left and right, nodding, and shaking head. Then, time-frequency spectrograms were obtained by short-time Fourier transform, from which we can see that different body gestures have different polarimetric MDSs. Finally, we propose to classify four body gestures using the deep convolutional neural network (DCNN) method. It is shown that by combining HH and HV polarizations, about 92.7% recognition rate is achieved while only about 77.5% and 89.3% rates are obtained by using single HH polarization and single HV polarization, respectively.
Global Positioning System (GPS) is an excellent application example of satellite communication technology. And it is widely used in navigation, measurement, and time service. However, GPS receivers are vulnerable to unintentional interference or jamming because they rely on external radio frequency (RF) signals. RF interference signals can result in degraded navigation accuracy or complete loss of receiver tracking. Thus, GPS receivers have anti-jamming ability to relieve the effect of interference or jamming. In order to improve the anti-jamming performance of GPS receiver, it is of great theoretical significance and practical application value to study the influence of interference on GPS receiver. To this end, this paper investigates the performance of integrator in the presence of single-tone interference in GPS receiver, and a single-tone interference method based on frequency difference is proposed. Specifically, the analytical relationship between single-tone interference and integrator output is given. Then, it shows that the output of integrator depends not only on the power of single-tone interference but also on the frequency difference between single-tone interference and GPS signal. Finally, the vulnerability of integrator or GPS receiver to the presence of interference increases if the frequency difference satisfies the specific condition. Simulation results show that the proposed method is able to improve the chip error rate in GPS receiver.
Due to the limitations of low-resolution radar system and background clutter, the task of target classification with conventional low-resolution radars is relatively difficult. This paper introduces fractional Fourier transform (FrFT) to process aircraft echoes in order to find the optimal fractional Fourier domain, in which signal to noise ratio can reach the maximum, and then applies multifractal theory to the feature extraction of radar targets. Based on the above, we use SVM to do target classification. Experiments show that the multifractal characteristics of aircraft echoes can be enhanced by FrFT, and the features extracted from the optimal fractional Fourier domain can be used effectively to classify different types of aircraft even in the case of low SNR.
This paper presents a polarization-insensitive frequency selective rasorber which has high in-band transmission at high frequency and wideband absorption at low frequency based on square-loop and parallel LC resonance. The rasorber consists of a bandpass FSS and a resistive sheet plus a slot-type metallic four-legged loaded element as the bandpass FSS element. The resistive element is realized by inserting several strip-type parallel LC structures into a resistor-loaded square-loop element, which allows the surface current to be controlled as necessary and the wave at the resonance frequency to be passed with minimum insertion loss. Wideband absorption is realized at low frequency, where the bandpass FSS is nearly totally reflected, and the FSR performs as an absorber. Simulation results show the transmission band at 9.9 GHz with transmissivity higher than 96% and the absorption band with absorptivity higher than 85% from 2.83 GHz to 8.6 GHz for TE-polarized 30˚ incidence and from 3.22 GHz to 8.48 GHz for TM-polarized 30˚ incidence. The absorptive/transmissive performance of the FSR structure is also verified ed by experimental measurements.
Rotationally symmetric sparse circular arrays are synthesized under multiple constraints. By combining the modified differential evolution algorithm based on the harmony search (in short HSDE) with the vector mapping (VM) method, a hybrid algorithm, called VM-HSDE, is proposed for synthesizing sparse circular arrays with low sidelobe levels. Due to the array's specific geometry, the number of optimization variables is reduced, and the constrained optimization problem is simplified. Moreover, infeasible solutions are avoided, and the problem is effectively solved by the VM-HSDE algorithm. Finally, three pattern optimization results verify the effectiveness and reliability of the VM-HSDE algorithm.
This work proposes new filter design techniques to improve the out of band spurious performance of integrated ceramic waveguide filters and ceramic loaded filters. Various resonators of different types like non-uniform width, TEM and half ridge were used. The proposed filter designs offer a considerable miniaturization and significantly improved spurious performance up to 85% without compromising the figure of merits of the filters like Q-factor, return loss, etc. Two sixth order filters with best in-band and out-band performance have been fabricated. Measured results of the fabricated filters are in good agreement with the computer simulations, which confirm the validity and accuracy of designs.
A compact tri-band antenna incorporated with split ring resonator array is proposed for Wireless Local Area Network (WLAN) and Worldwide interoperability for microwave access (WiMAX) applications. The proposed antenna is printed on an FR4 substrate with overall dimensions of 0.25λx0.29λ at the lowest frequency. Impedance bandwidth of the antenna is optimised by introducing slots on the top of the patch. The ground plane is engineered by placement of a split ring resonators array to induce additional resonance due to occurance of magnetic dipole moment.The antenna resonates at the frequencies of 2.4 GHz, 3.5 GHz & 5.5 GHz having bandwidths of 12.5%, 7.42% and 6.36% with gains of 2.25 dBi, 3.72 dBi and 2.71 dBi, respectively which matches well with the fabricated results. The proposed antenna shows omnidirectional radiation pattern which makes it appropriate for WLAN and WiMAX applications.
We provide a general and rigorous formulation of antenna localized electromagnetic radiation energy in generic antenna systems based on Poynting flow instead of the spectral approach proposed earlier. The main theory is first developed using the principles of energy-momentum conservation and the center-of-energy theorem, culminating in the derivation of a direct localized energy expression. It is rigorously established that this expression satisfies the main features expected of physical energy, mainly positive definiteness and regularity. The obtained formula involves only the radiated fields (no current or charge) source and is easier to compute using specialized direct time-domain EM solvers. The proposed approach is expected to play a role in understanding energy localization in coupled antennas and shed light on gain enhancement methods.
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