Volume 77, Issue 7-8

In this paper, we propose the use of the graphics processing units (GPUs) for acceleration of solution of the H-polarized electromagnetic waves scattering by strip gratings. The approach combines the boundary integral equation method with the Nystrom-type discretization of singular integral equations and is realized with the use of C++ and OpenCL. The elements of the matrix of the resulting system of equations can be calculated independently and, thus, in parallel. The calculation time of the proposed parallelized algorithm on GPU is compared to standard serial algorithm executed on CPU. We considered gratings of graphene strips in vacuum and inside a dielectric slab. The acceleration is up to 35–55 times for the gratings in vacuum and up to 80–140 times for the gratings of 5–20 strips inside the dielectric slab.

This article is devoted to the study of electromagnetic scattering characteristics in arid areas, and proposes environmental monitoring and improvement methods. A four-component soil dielectric model was established to study the relationship of soil dielectric constant with soil moisture and frequency. As the Monte Carlo Method combined with Gaussian spectral function was used to simulate the actual dry ground, the Sparse Matrix/Canonical Grid (SMCG) algorithm model based on the surface current equation was established to calculate the electromagnetic scattering coefficient of arid areas. To verify the correctness of the proposed algorithm, the results obtained by SMCG was compared with those calculated by Method of Moments (MOM), which showed great consistency. Many results were obtained by using the algorithm in this paper, based on the measured soil data in the southeastern area of Ejin Banner, Inner Mongolia. It was found that soil moisture content, area roughness and incident electromagnetic wave segment had influence on the scattering echo and showed regular change. The results of this paper are of guiding significance for soil moisture monitoring, desertification control and agricultural planting in arid areas.

The article presents the design and development of a metamaterial-based microwave absorber having polarisation insensitivity, broad angle of incidence, low profile, and compactness in the microwave frequency range. The unit cell focuses to achieve maximum absorption at C-, X- and broad Ku-bands. The structure is simulated and the results are analysed for different angles of polarisation and angle of incidence. The dimension of the proposed structure is ultrathin and compact having an overall dimension of 8 mm × 8 mm × 0.8 mm. The dimensions are optimized in such a fashion to achieve three different peaks at three different bands thereby making the triple-band behaviour of the metamaterial absorber possible. The structure is providing absorption of 99.14% absorption at 6.08 GHz (C-Band) while absorption of 98.29% is achieved at 9.49 GHz (X-band) and 265 MHz bandwidth with above 95% absorption from 16.57 GHz to 16.83 GHz (Ku-Band) in the microwave regime. The absorber patch is a composition of square ring patches and a central square ring annexed with triangles on four sides, the split ring providing a combinational effect witnessing the desired absorption at designated frequencies. The unit cell dimension at a lower cut-off frequency is 0.162 λ lowest . The proposed structure is verified for polarisation sensitivity and has a wide angle of incidence. The structure is experimentally verified for results and is found to be in close agreement with simulated ones. The compactness of structure with the attainment of the highest form of absorption in different bands including the 265 MHz high absorption band provides the scope of applicability in various engineering applications at microwave regimes.

This article deals with design and development of a novel 7th order low-pass filter with defected ground structures for S-band applications. The proposed LPF structure was comprised of dumbbell shaped interdigital defected ground structures and open stubs as series inductor and shunt capacitor in the pass band. In addition, an equivalent circuit model was derived and optimized to achieve a 3-dB cut off frequency about 4 GHz with a reflection coefficient of better than −20 dB. Moreover, proposed low-pass filter was manufactured on a Rogers RO4003C substrate with a dielectric constant of 3.38, the dissipation factor of 0.0027. The developed LPF has a very flat pass-band with a transmission coefficient less than −0.5 dB and the measured transmission coefficient better than −18 dB in the passband (DC-3.6 GHz). Meanwhile, the prototype has a 20 dB harmonic suppression level in the frequency range from 5.54 GHz up to 43.5 GHz. Furthermore, the measured peak to peak group delay variation was less than 170 ps in the passband. The proposed filter has a very compact size of 195.3 mm 2 .

In this article, two dual-band microstrip bandpass filters (BPFs) with high selectivity and independently controllable passbands are designed based on three parallel-coupled lines (TPCLs). The first BPF proposed in this paper is achieved by employing a pair of folded F-type resonators (FFRs) and conventional TPCL structure. By adjusting the above parameters of each FFR, the center frequencies of the two passbands can be controlled easily. In the meantime, TPCL can enhance the coupling between the source and load, and introduce multiple transmission zeros (TZs), which can conduce to a higher selectivity. To obtain superior selectivity, the second BPF is designed based on a novel TPCL. The novel TPCL is based on the traditional one, which further enhances selectivity since transmission paths are doubled. In order to achieve miniaturization and enhance coupling, FFRs are folded. In addition, four transmission zeros (TZs) are generated to improve the selectivity of the two passbands. The measured results of the fabricated BPFs centered at 2.45/3.5 GHz agree well with the simulated ones, which validates the proposed design method.

Intelligent reflecting surface (IRS) is an emerging and low-cost revolutionary technology that can be deployed in future communication systems to enhance data transmission performance. An IRS comprises a lot of small, passive, and low-cost elements that can smartly reflect the incident signal from the transmitter to the receiver. In this paper, an IRS-enhanced multiple-input multiple-output (MIMO) downlink network is considered, in which a cell-edge user receives the data signal from a base station (BS). In this network, the direct path between the BS and the user is blocked by an obstacle, and the user receives only the tunable reflected signal from the IRS. To achieve spatial diversity, beamforming is applied to the antennas at the BS and the user. The goal is to jointly design the transceiver beamforming vectors and the IRS reflection coefficients so that the signal-to-noise ratio (SNR) of the user is maximized. Since the IRS elements are passive, the amplitude of the IRS reflection coefficients must be equal to or smaller than one. The constrained SNR optimization problem is non-convex. We propose a three-step procedure to obtain an effective sub-optimal solution for this problem. Accordingly, an innovative non-iterative algorithm is proposed to design the problem parameters. Simulation results show that the IRS-enhanced MIMO downlink system, in which the proposed non-iterative algorithm is used to develop the network parameters, outperforms the conventional network without IRS in terms of bit error rate (BER).

In this paper, a wide bandwidth (20 GHz) and small sized (200 × 200 × 50 µm 3 ) terahertz (THz) square graphene ribbon antenna using Photonic Band Gap (PBG) substrate are investigated in the 0.6–0.8 THz band. The proposed antenna consists of graphene as radiating patch mounted on four types of ground plane. The important aim of this work is to eliminate the second resonance frequency by utilize a several types of ground plane and keep a single frequency by improving the performance of the proposed antenna. The effect of change ground plane on the performance of antenna is compared, in terms of reflection coefficient, bandwidth, directivity and radiation pattern. The antenna has achieved good gain (7.62 dB) and good directivity (6.38 dB) in comparison to work reported in the literature.

In this paper, a Decoupling Nearfield Surface (DNS) is designed above the antenna, to reduce the mutual coupling of closely two or more patch array. In this way, the electrical and magnetic distributions are utilized to demonstrate the mechanism of isolation. The proposed DNS element creates the electric field distributions with an orthogonal mode and the magnetic field distributions with excitation in substrate such that the effective suppression of antenna mutual coupling is obtained. The DNS element can be easily applied to the Multiple-Input Multiple-Output (MIMO) antennas that having multiple patch elements. Moreover, the proposed structure is implemented practically and simulated for a patched antenna. The measurement and simulation results verifies that the isolation is more than 20 dB and the isolated impedance bandwidth is about 7%.

This paper presents a compact dual-band open-loop monopole MIMO antenna to serve 4G/5G applications. This antenna consists of two printed monopole antennas with very high isolation. Two enhancement techniques are utilized to improve the isolation between ports. Since each technique can provide high isolation of a single band, a combination of λ /4 slot and T-shape techniques are used to achieve high isolation of −19 dB and −35 dB at 2.4 GHz and 3.5 GHz, respectively. The proposed design has high efficiency, a low envelope correlation coefficient, and an acceptable level of realized gain (2.7 dBi and 2.2 dBi) at low and high bands. This design has been fabricated using low-profile printed circuit technology with a compact patch size of 50 × 25 mm 2 based on an FR-4 substrate. Moreover, the simulation and measurement results are in good agreement.

In order to minimize antenna complexity and improve gain, a new compact size low profile SIW-cavity-based frequency reconfigurable antenna is presented for IoT, WLAN, and 5G applications. The proposed antenna miniaturization is achieved by incorporating SIW cavity using metallic vias. The reconfiguration mechanism is accomplished by etching a circular ring slot and a C-shaped slot at the top metallic layer of the substrate. The frequency switching mechanism from low to high state is provided by eight PIN diodes. The diodes are placed in a symmetrical order along circular ring slot. All the diodes are switched on simultaneously to achieve low-frequency state operation. However, the off state of the diodes shifts antenna operation from low to high-frequency state. The antenna is fabricated on a small size substrate with an overall electrical size of (0.4 λ * 0.4 λ ).The proposed antenna resonates at frequencies 2.4, and 3.45 GHz with 220 MHz and 470 MHz bandwidth respectively in low-frequency state. In high-frequency state, the antenna resonates at 5.8 GHz with 200 MHz bandwidth. The proposed antenna achieves peak gain of 6.3, 6.7, and 5.9 dBi in the three bands, and stable radiation patterns are attained in the working frequency band of the antenna.