Volume 78, Issue 5-6

This article proposes a method for two-port vector network analyzer (VNA) calibration that uses a line standard and three or more offset-reflect standards (L n Γ, where n is the number of offset-reflect standards and n  ≥   3). The reflection coefficient of the highly reflecting offset-reflect standards and the propagation constant of the transmission line are unknown for this calibration method, but they can be obtained in the process of calculating the VNA calibration error coefficients. In the L n Γ calibration method, the calibration fixtures are all equal in mechanical length. Therefore, compared with the thru-reflect-line (TRL) method, this calibration method is convenient when the test fixtures of both sides of the VNA are fixed or difficult to move during the measurement. To further simplify the experimental operation, a corrugated reflector is also designed. In this calibration method, only one corrugated reflector used as the offset-reflect standard is needed. Different offset-reflect standards are realized easily by changing the position on the microstrip line. The proposed L n Γ calibration method is accurate, which is proven by theoretical analysis, simulations, and measurements.

This paper presents an accurate and efficient semianalytical method based on the Galerkin procedure for solving electromagnetic wave propagation problems in multilayer inhomogeneous cylindrical dielectric waveguides. The method represents the field in each inhomogeneous layer by a linear combination of eigenfunctions with unknown coefficients, which are expressed using the inner products of a series of basis functions, following the Galerkin procedure. The continuity of the field and its radial derivative is enforced at the interface between adjacent layers. By applying this procedure to all inhomogeneous layers, the Helmholtz equations are transformed into linear algebraic equations with expanded coefficients in matrix form, allowing the complicated wave propagation problem in a multilayer inhomogeneous waveguide to be solved as a matrix eigenvalue problem. The method is validated by providing detailed propagation characteristics for various multilayer inhomogeneous cylinders with different permittivity profiles. The accuracy and efficiency of the proposed method are demonstrated through comparisons with results obtained using other numerical techniques.

While reverse time migration (RTM) algorithm is commonly used in geophysical explorations, this paper addresses the RTM imaging procedure for reconstructing of lossy dielectric discontinuities in a planar waveguide using electromagnetic waves at a single frequency. The direct problem of the related configuration is solved via method of moments (MoM) to produce the synthetic scattered data to be used in RTM. The achievements of the method are examined and verified by including different numerical examples. It is shown that the RTM approach can be used as an alternative imaging methodology in parallel plate waveguide problems.

This paper proposes a microstrip filter with controllable transmission zeros based on the λ /4 stepped impedance resonator. This filter utilizes hybrid electric-magnetic coupling to generate transmission zeros, which can improve selectivity and stop-band performance. A fifth-order filter is designed and manufactured on a ceramic substrate with a center frequency of 26 GHz, bandwidth of 2 GHz and the signal suppression level is better than 42.51 dB from 10 to 22.8 GHz and 48.23 dB from 29.1 to 40 GHz. Furthermore, the proposed filter has a compact size of 2.074 × 1.071 mm (0.566 λ g  × 0.292 λ g ).

The state of the art for wearable antennas for wireless communication and biological applications is compiled in this article. It addresses a wide range of subjects, such as how to use novel materials like Artificial Magnetic Conductors (AMC) and Metamaterial (MTM) structures to enhance antenna performance. It also covers the design of dual-band and reconfigurable antennas and the use of machine learning to optimize aerial design. The main subject of this article is how wearable antennas could lead to advancements in wireless communication and healthcare in the future, perhaps improving lives worldwide. It includes implantable antennas, textile-based antennas, and various flexible graphene-based antenna varieties. The use of wearable antennas for brain stroke diagnostics, wireless body area networks, telemedicine, and breast imaging is covered in this study. Additionally covered are reconfigurable antennas based on Metamaterial (MTM)structures and Wideband on-body antennas inspired by Metamaterials (MTM), both of these applications are useful in the assembly of wearable antennas, which is the main goal of this work. The research also discusses how metamaterials (MTM) might raise the sensitivity of the bioelectric field, enabling precise bioelectric signal monitoring. Metamaterial (MTM) antennas function reliably in a range of biomedical applications and can adjust to the electromagnetic properties.

Based on the theory of coplanar waveguide (CPW) transmission line, a novel microwave non-destructive strain monitoring sensor specifically designed for cement-based material structures is presented in this study. The aim is to establish the relationship between the variation of the S11 phase parameter of the CPW strain sensor and the structural strain, utilizing a linear analysis. The feasibility of the strain monitoring by the CPW sensor is validated through simulations and experiments. The obtained results demonstrate a strong linear correlation between the phase change of the S11 parameter and the strain, with a goodness of fit of 0.987. The simulated strain sensor exhibits a sensitivity of 48.83 ppm/με, while the experimental measurement sensor shows a sensitivity of 65.82 ppm/με. These findings highlight the potential significance of the proposed method, offering a new approach that is characterized by high sensitivity, low cost, and simplicity for strain monitoring in concrete structures. Among them, the sensor cement mortar matrix made in this study was mixed with the recycled material made of waste glass steel FRP after a certain treatment process. The development of this method holds promise for the advancement of health monitoring in concrete structures.

A novel, high-gain reconfigurable antenna with a metasurface (MS) superstrate-based configuration is proposed in this research article. The design utilizes a concentric octagonal-shaped patch as a base antenna. Four SMP1345-079LF PIN diode switches are incorporated in the base antenna to facilitate frequency reconfiguration. When all four of the diodes are in OFF condition, the designed antenna resonates at 5.8 GHz. Switching ON the diodes switches the resonating frequency to 5 GHz. A novel MS unit cell of shape like ‘8’ has been designed and analyzed. The designed unit cell exhibits properties of the metamaterial in the operating frequencies. An MS superstrate of a 5 × 5 array has been designed and connected to the base antenna through Teflon rods. Further, the proposed reconfigurable antenna with MS has been analyzed for air and foam medium (medium between antenna and superstrate). The proposed structure offers better performance for the air medium with a gain enhancement of 4.23 dBi and 1.55 dBi at 5 GHz and 5.8 GHz respectively. Fabrication and testing processes are undertaken to validate the proposed antenna’s performance.

We proposed a high gain high-efficiency compact metallic resonator antenna operating at even-mode meander line spoof surface plasmon polaritons (MLSSPPs). The high radiation efficiency is caused by the bulk of fields crowded in lossless air near the antenna rather than in lossy dielectric as in conventional dielectric resonator antennas (DRAs). The proposed antenna also exhibits compact size because of its high effective refractive index. A reliable equivalent circuit model is proposed for the design of the resonator antenna with basic mode of half wavelength resonant mode. As an example, a meander-line SSPP antenna is designed, fabricated and measured. Both the simulated and measured results show the advantages of high efficiency and compact volume. In addition, the antenna achieves higher gain and wider relative bandwidth per wavelength cube volume compared with its counterparts. This method provides a good alternative for designing DRAs.

A simple technique for gain enhancement of irregular hexagonal shaped ultra-wide band (UWB) slot antenna by inclusion of closely packed tessellated rhombic loop (TRL) based FSS is presented in this paper. The slot antenna is designed to cover entire UWB (3.1–10.6 GHz) frequency range with stable bi-directional radiation pattern. Also, it exhibits non-uniform boresight gain in zenith ( θ  = 0°) and nadir ( θ  = 180°) directions. The slot antenna is further loaded with TRL FSS at both slot and feed side separately to study distinct configurations of antenna integrated with FSS and evaluate the impact of the configurations of FSS on antenna performance. Later, an antenna and antenna loaded with TRL FSS prototype are developed for experimental validations. Through measurements it is found that the slot antenna covers entire UWB frequency band and provides a maximum of 4.31 dB gain in zenith direction while 4 dB gain in nadir direction. A gain enhancement of 2.44 dB in zenith and 3.8 dB in nadir directions are achieved when the slot antenna is integrated with TRL FSS along feed side and slot side separately. The measured results confirm the simulated results well.

The paper proposes a high gain, low ECC, and high isolation THz MIMO antenna array for future generation wireless applications to accommodate a growing population of mobile users. A THz MIMO antenna array is designed with dimensions of 1200 × 2200 × 191.29 µm 3 . It employs the array of double-slit complementary split-ring resonators (D-CSRRs) on the bottom layer to improve the gain, return loss, and isolation. The gain of the proposed antenna array is 11.3 dBi with 66.45 % radiating efficiency at 0.65 THz. The −10 dB impedance bandwidth lies from 0.62–0.66 THz. The parameters of the MIMO antenna are evaluated such as isolation, envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss. The ECC and DG value observed are 2.84 × 10 −6 and 9.98 dB, respectively, at 0.65 THz. The channel capacity loss and isolation of the proposed MIMO antenna array are below 0.4 bps/Hz and (| S 21 | > 25 dB), respectively, in the complete operating band. The suggested THz MIMO antenna array can be utilised for THz high-speed wireless communication, video-rate imaging systems, sensing, the medical field for cancer imaging, security scanning, and the detection of illicit goods.