In this paper, a novel wide axial ratio bandwidth (ARBW), high gain, and low profile left-hand circularly polarized [4×4] elliptical microstrip array suitable for Ku-band satellite TV reception applications is introduced. A careful study has been done to get the optimum design to be suited for these application requirements. A circularly polarized microstrip patch with two stubs opposite to each other to produce two orthogonal modes is presented. The proposed element has 1.49 GHz 10-dB return loss bandwidth (RLBW), 0.44 GHz 3-dB Axial-ratio band (ARBW), and 6.9 dBi gain. A novel substrate integrated waveguide (SIW) feeding structure is investigated. Using the advantage of the output ports phase response of the SIW feeding network, two structures have been investigated. First, a [2×2] circular array has been designed, and although it has reached a good RLBW, this structure dose not achieve the required ARBW for the above-mentioned application. Further, a compact [2×2] sequential feeding network is designed to widen the ARBW. The measurement shows a very good result with about 12 dBi gain, 14.8% RLBW, and 12% ARBW. Finally, a [4×4] duple sequential feeding array is designed to increase the gain of the antenna to about 19 dBi, with 13% RLBW and 20.7% ARBW. In addition to that, the final antenna profile is 0.0184λ.

In this article, the body shape and complex permittivity determination employing inverse electromagnetic scattering problem solution for two-dimensional cases is considered. The method of auxiliary sources (MAS) is used as a mathematical apparatus. Several body shape cases are considered, and the efficiency of the approach is shown. The program package is created based on this method, and the numerical experiment results are presented.

In this paper, a wideband antenna is designed systematically based on characteristic mode analysis (CMA). The antenna consists of a rectangle, a semi-annular ring, and a microstrip line. The radiating behavior and resonant frequencies of the radiating element are analyzed by using first four characteristic modes. First two modes only have wideband behavior and are excited by CPW feeding technique. The proposed antenna is printed on a low cost FR4 substrate with a size of 35x50x1.6 mm³ and impedance bandwidth ranging from 1.6 to 3.8 GHz for the applications of GSM, DCS, LTE, and WIMAX. To validate the proposed approach, the wideband antenna is fabricated and tested. A wide impedance bandwidth of 81% with |S₁₁| < -10 dB is achieved for both simulation and measurement results.

A dual-band circularly polarized (CP) patch antenna with wide 3-dB axial ratio beamwidth (ARBW) is presented for BeiDou Navigation System (BDS). Simple stacked circular patches are used as the main radiations for achieving dual-band operation. To enhance the ARBW for the two operation bands, an annular metal strip loaded ground plane (AMSL-GP) is presented. Besides, edge resistors are inserted to the GP for further ARBW enhancement at the lower band. In realization, a compact single-input feed network based on a coupled-line trans-directional (CL-TRD) coupler is designed to provide two orthogonal modes at the two frequency bands simultaneously. Experimental results show that the bandwidth for 10-dB return loss is from 1.15 GHz to 1.65 GHz, which covers BDS B1 (1.561 GHz) and B2 (1.207 GHz). The 3-dB axial ratio (AR) bandwidths for the lower and upper bands are 9.6% and 7.1%, respectively. At 1.207 GHz, the antenna has 3-dB ARBWs of 185° and 187° in the xoz and yoz planes, respectively. And the values are 192° and 194° at 1.561 GHz.

Available of multiple illuminators in a multistatic airborne passive synthetic aperture radar (SAR) system can enhance SAR imaging quality. In this paper, a new imaging algorithm based on two-level block sparsity for a multistatic airborne passive SAR system is proposed. The proposed imaging algorithm named by two-level block matching pursuit (BMP) algorithm utilizes both the spatially clustered property of observed targets and joint sparsity of the multistatic observation, i.e. two-level block sparsity to achieve imaging reconstruction of an observed scene. The simulation results show that the proposed two-level BMP imaging algorithm for the multistatic airborne passive SAR system can reduce imaging reconstruction time and provide enhanced imaging reconstruction quality compared to the state-of-the-art structured sparse imaging algorithm.

A new approach to design a microstrip ultra-wideband (UWB) bandpass filter (BPF) with quad sharply notched bands and good selectivity is proposed using quad parallel defected microstrip structures (PDMSs). The initial UWB BPF comprises interdigital coupled lines and an E-shaped multiple-mode resonator (EMMR) to achieve two transmission zeros on both sides of the passband thus to improve skirt selectivity. Then, four PDMSs are introduced, which have the properties of achieving four band-notched characteristics and provide high degree of adjusting freedom. To validate the design theory, a new microstrip UWB BPF with four notched bands respectively centered at 5.3, 5.9, 6.4, and 7.4 GHz is designed and fabricated. Both simulation and experimental results are provided with good agreement. The designed methodology is very efficient and useful for filter synthesis though the design principle is simple.

The extending applications for mobile computing have experienced immense progress over the previous decade. However, this has ultimately influenced the shortage of bandwidth. Therefore, to fulfill the consumers' demand, inexpensive antennas need to be uniquely designed for the next/fifth generation (5G) frequency spectrum. Consequently, this paper presents a novel antenna composed of inductors (L) or capacitors (C) on an air-substrate. Zinc (Zn) and copper (Cu) materials are utilized to fabricate the lumped LC resonator prototype. The effects of antenna's and substrate's thickness on resonant frequency or bandwidth have been studied. The finalized configuration engaged 1113 sq. mm area and operated at 28 GHz with approximately 3 GHz bandwidth. At resonant frequency, the system demonstrates peak gain and efficiency values of 10.6 dBi and 91%, respectively. The core objective of this paper is to report an antenna featuring simple and economical design along with premium results for 5G mobile terminals.

This paper investigates the joint direction of departure (DOD) and the direction of arrival (DOA) estimation of coherent targets in bistatic multiple-input multiple-output (MIMO) radar under the presence of spatially correlated noise. Based on electromagnetic vector sensors at both transmitter and receiver of MIMO radar, a preprocessing method, namely polarization difference smoothing, is proposed to remove the coherence between targets and to suppress the spatially correlated noise. Then DOD and DOA are estimated using the ESPRIT method. Further, this paper develops a simple approach for pair-matching between the estimated DODs and DOAs. Simulation results are compared with the receive polarization smoothing and transmit-receive polarization smoothing methods available in literature. Results show that the proposed approach improves the performance significantly.

In this paper, a novel nested array is proposed for direction of arrival (DOA) estimation of noncircular signals. By using the noncircular property, the resulting virtual array is composed of difference coarray (DCA) and sum coarray (SCA). Specifically, we first give the properties of DCA and SCA for generalized translational nested array. Then, based on the relationship between DCA and SCA, an optimal translational nested array with increased degrees of freedom (DOFs) is constructed. To extend the physical array aperture, we move part of sensors in the translational nested array to the mirrored locations. Accordingly, the novel nested array with increased DOFs and physical array aperture is obtained. Finally, superiority of the proposed array is demonstrated by simulation experiments.

We have simulated ionospheric disturbances generated by the buoyancy and electrodynamic effects in a two-dimensional configuration in the vertical plane in the ionospheric F region using a simple two-dimensional mathematical model for internal gravity waves propagating in the lower atmosphere, and we have investigated the characteristics (e.g. buyoancy frequency, wavenumber, wavelength, speed) of the ionospheric disturbances. We find that electrohydrodynamic effects are mainly responsible for small scale non-travelling ionospheric disturbances, while magnetohydrodynamic effects are responsible for travelling ionospheric disturbances, including small scale travelling ionospheric disturbances (SSTIDs), medium scale travelling ionospheric disturbances (MSTIDs) and large scale travelling ionospheric disturbances (LSTIDs). Our results are in agreement with the results obtained from observations.

We propose a new method to match diplexer channels with a common port in which a π-shaped strip conductor is used as a matching circuit. The applicability of the method is illustrated by simulating and fabricating a microstrip diplexer for GPS/GLONASS applications. The central frequencies of the channels are 1.234 GHz and 1.597 GHz, and their fractional bandwidths are 6.8% and 7.3%, respectively; minimum insertion losses are 1.05 dB and 1.08 dB. The main advantage of the diplexer is its compact size: 16.8 mm × 11.0 mm × 6.4 mm in housing. Using 1D models and a quasi-TEM approach, the frequency-dependent coupling coefficients between the matching circuit and input resonators of the channels are calculated, and the influence of the matching circuit's geometrical parameters on its coupling with diplexer channels is studied.

Development and optimization of printed spiral coils have significant impacts on the efficiency and operating range for magnetic resonant wireless power transfer (WPT) applications. In this paper, the effects of different material losses (substrate and conducting coating) of printed coils are considered and experimentally studied in this paper. For the purposes of comparison and finding the dominated losses, lossy loaded capacitors with equivalent series resistances have also been investigated. A four-coil system with an external capacitor-loaded (ECL) magnetic resonant WPT system is considered, and a self-resonant coil is designed and compared. Results show that the ECL resonant coil has higher efficiency than the self-resonant coil with the same size and distance between the transmitting and receiving coils. Through observing the simulated results and analyzing experimental data, it can be concluded that the dominant cause of the decrease in efficiency of this ECL-WPT system is the strip resistive loss of coil of 57% and the ohmic loss in ECL of 37%. Meanwhile, the substrate loss significantly impacts on the efficiency of the self resonant coil. The overall measured efficiency is about 66% of the ECL coil at a distance of 50 mm when the above loss factors are considered. The measured results are in good agreement with the analysis and simulations.

The scattering of a transverse magnetic plane wave by a conducting cylinder partially buried in a dielectric half-space is solved by an aperture method. A system of coupled integral equations for the current induced on the cylinder and the scattered electric field at the dielectric interface are formulated from field equivalence principles. The scattered tangential electric field at interface is negligible at some distance from the cylinder location. Hence, for a sufficiently wide interface truncation, the coupled integral equations can be easily solved numerically by the Method of Moments. Data for the cylinder current, the scattered electric field at interface and the far-zone field are shown for cases of interest.

To realize the attractive Wifi-type magnetically coupled resonant (MCR) wireless power transfer (WPT) techniques, not only the optimization of power and efficiency but also the spatial energy distribution characteristics (EDCs) should be considered. In this paper, the EDCs of three two-coil systems including an alignment system and systems with an angular and lateral misalignment are explored by the Poynting vector, and unified expressions of the active power density (APD) and reactive power density (RPD) are provided. Also, it is found that the APD is mainly distributed in the transmission path, and the RPD is mainly composed of three parts. When the phase difference between the currents in the transmitter and receiver tends to be π/2, the APD increases, and RPD decreases. The active power through an arbitrary infinite plane which intersects the transmission path but does not intersect the coupler is found equal to the transferred active power of the system, which is consistent with the results obtained by the circuit theory. Furthermore, the directionality of the APD is determined, and the APD is utilized to explain the coupling impedance in circuit theory. Then four basic reactive power compensations are considered, and it is recommended to use heavy load for the system with parallel compensation on the secondary side. Finally, the theoretical analysis is verified by simulation and experiment. This paper provides a significant reference for the analysis and design of the MCR WPT system and the improvement of the electromagnetic environment around the system.

This paper presents the design and analysis of a dual-band circularly polarized (CP) microstrip patch antenna for WLAN and vehicular communication applications. In this antenna, an L-shaped slot is cut, and a square parasitic patch with diagonally opposite corners cut is loaded in offset beneath to monopole antenna to realize dual band CP response with wideband response. The antenna exhibits dual band CP response at 2.45 GHz (WLAN) and 5.9 GHz (Vehicular) having 20.45% and 15.73% of simulated impedance bandwidth and 6.84% and 14.16% of axial ratio bandwidth for WLAN and Vehicular band respectively. The measured impedance bandwidth (S₁₁ < -10 dB) is 19.43% and 12.73% for WLAN and vehicular band respectively. The antenna design is simple and fabricated using an economical glass epoxy FR4 substrate with size of 45 × 40 mm². The measured results are found in good agreement with simulated results. The proposed antenna is analyzed using transmission line equivalent circuits, and the details are presented and discussed.

Electrical impedance tomography (EIT) is a technique for reconstructing conductivity distribution by injecting currents at the boundary of a subject and measuring the resulting changes in voltage. Sparse reconstruction can effectively reduce the noise and artifacts of reconstructed images and maintain edge information. The effective selection of sparse dictionary is the key to accurate sparse reconstruction. The EIT image can be efficiently reconstructed with adaptive dictionary learning, which is an iterative reconstruction algorithm by alternating the process of image reconstruction and dictionary learning. However, image accuracy and convergence rate depend on the initial dictionary, which was not given full consideration in previous studies. This leads to the low accuracy of image reconstruction model. In this paper, Recursive Least Squares Dictionary Learning Algorithm (RLS-DLA) is used to learn the initial dictionary for dictionary learning of sparse EIT reconstruction. Both simulated and experimental results indicate that the improved dictionary learning method not only improves the quality of reconstruction but also accelerates the convergence.

A novel dual-frequency antenna with horizontally polarized (HP) omnidirectional radiation is presented in this paper. The antenna consists of four printed arched dipoles, four planar baluns and a four-way power splitter. The balun as well as the power splitter works as the feed network. By loading a transmission line resonator (TLR) as the near-field coupling parasitic element, the dual-frequency characteristics can be realized. After the design principle is stated, a sample antenna is manufactured and measured to prove the predicted performance of the proposed antenna. The measured results agree well with the predicted ones.

In this paper, a dual unmanned aerial vehicle (UAV)-enabled secure communication system with simultaneous wireless and information and power transfer (SWIPT) has been investigated. Specifically, assuming that the energy receivers (ERs) may be potential eavesdroppers (Eves), we aim to maximize the minimum secrecy rate among multiply legitimate receivers (LRs) within each period by jointly adjusting the UAVs' trajectories and power control (PC). Since the resulting optimization problem is very difficult to solve due to highly non-convex objective and constraints, we equivalently transform it into a more tractable problem via successive convex approximation (SCA) and constrained concave-convex procedure (CCCP), then propose an iterative method. The simulation results show that the proposed joint optimization algorithm achieves significantly better performance than the conventional algorithms.

In this paper, the performance of relay selection in an energy harvesting aided mixed radio frequency (RF)/free space optical (FSO) system with transmit antenna selection (TAS) over atmospheric turbulence and pointing error is presented. The source of multiple antennas employs TAS to send information to the destination via multiple relay nodes. Also, the energy-limited source uses selection combining technique to harvest energy from multiple relay nodes. As a result, all the relay nodes act as a wireless power transmitting node as well as data receiving node. Moreover, it assumes that the RF/FSO links follow Rayleigh/Malaga (M) distributions with non-zero boresight (NB) pointing error on the FSO link. Therefore, the system outage probability closed-form expression is then derived which is utilized to obtain the system throughput. In addition, the results demonstrate the significant effect of atmospheric turbulence and NB pointing error on the system performance with multiple relays, and source transmit antenna offers the system better performance. The accuracy of the derived expressions is thus validated through Monte Carlo simulations.

An approach to synthesizing wideband ultraminiaturised-element frequency selective surface (UMEFSS) based on interlocked 2.5-dimensional (2.5D) structures is proposed. Ultra-miniaturisation and wide stopband response can be realized due to compactly staggered arrangement of 2.5D elements. The element size of the proposed UMEFSS is reduced to 0.033λ₀×0.033λ₀, and fractional bandwidth attains 99.8%. Stable response is achieved under oblique incidence at different polarisations. The results show a satisfactory consistency between full-wave simulations and experiments.