Kalarickaparambil Joseph Vinoy

This letter presents a 2× 2 microstrip patch MIMO antenna on a suspended substrate optimized for the n78 5G band with enhanced isolation performance. Several decoupling methods, including grounding metallic strips between patches, placing a metallic cross -shaped wall under the substrate, and truncating patch corners, were analyzed by simulations to assess their effectiveness. Key geometric parameters affecting isolation were studied using their equivalent circuits before integrating all these methods into the proposed MIMO array. This array achieves a 6.67 dBi peak gain, 26.46% impedance bandwidth, and 17.2% decoupling bandwidth for isolation better than 20 dB. This design offers an excellent channel capacity loss (CCL), making it suitable for 5G base station antennas.

Numerical electromagnetic computations must often accommodate random geometric representations while handling biological tissues, and engineered components with manufacturing tolerances. Meshless time-domain radial point interpolation method (RPIM) offers advantages to quantitatively analyze such geometric uncertainties using polynomial chaos expansion (PCE). Formulations for geometric uncertainties may require variations in mesh or node distribution for each analyzed sample, leading to high computational requirement for re-meshing. The proposed geometric stochastic RPIM (G-SRPIM) overcomes this with a single domain model by expressing the shape function matrix of RPIM in a stochastic framework. The uncertainty is quantified in G-SRPIM through a novel way by which its random support domain moment matrices are organized in a block structure, and inverted using Schur's complement and Neumann approximation, exploiting the underlying symmetry. The proposed method is validated by analyzing a parallel plate waveguide with a slit exhibiting random variations, a realistic 3D bio-electromagnetic problem involving a section of human head, and an iris filter with random variations in its iris dimensions. Standard deviation upto 45% of the average inter-node distance is tested without jeopardizing the stability. The accuracy of our approach is compared with Monte-Carlo (MC) simulations on a deterministic RPIM using the Kolmogorov-Smirnov (KS) test. Additionally, results are compared with MC simulation on CST$^{\text{\text{®}}}$ Studio Suit 2018$^{\text{™}}$ and stochastic collocation (SC). The proposed method exhibits superior execution time compared to SC and MC-based non-intrusive implementations, underscoring its efficiency and reliability in handling geometric uncertainties in microwave components.

Evaluation of uncertainty in field values at a defibrillator probe embedded inside human heart muscles helps in improving EMI/EMC design of the implants and setting the right thresholds for its safe operation in an environment with electromagnetic interference. Large variations in electromagnetic properties such as dielectric constant and conductivity, are expected in such problems. In this paper, a three-dimensional reduced stochastic radial point interpolation method (R-SRPIM) is developed for uncertainty quantification in bio-electromagnetics. Derivatives of field quantities in Maxwell’s equations are obtained using radial basis function, and stochasticity in the electromagnetic properties within the model space is incorporated into this formulation. The number of terms in the polynomial chaos expansion and hence the computational complexity increases with large variations. To make the resulting formulation computationally viable, sparsity of the stochastic matrix is enforced by utilizing linearization property of the product of three Hermite polynomials and using singular value decomposition. Accuracy of the proposed approach is validated using Kolmogorov Smirnov test, with Monte Carlo simulations and COMSOL multiphysics®.

Stochastic analysis using polynomial chaos expansion (PCE) based spectral stochastic finite element method (SSFEM) is computationally expensive and is impacted by the curse of dimensionality. In this paper, a low dimensional basis is developed to approximate the problem using proper orthogonal decomposition to employ PCE based SSFEM, thereby resulting in an efficient intrusive formulation for uncertainty quantification over a wide frequency band. Galerkin’s projection of vector finite elements for an electromagnetic problem with relative permittivity variations in multiple dielectric regions is formulated. The proposed method is shown to be computationally efficient and gives accurate results for a range of frequencies with single computation. It is also shown that this approach does not scale adversely with the number of stochastic parameters and has significantly lower memory requirement.

A wideband absorbing metasurface is proposed to improve the circularly polarized response of a 1-18 GHz low profile Archimedean spiral antenna. The metasurface consisting of surface mounted resistors between metallic patches in a circular arrangement is placed on the opposite side of antenna substrate. After analyzing the unit cell behaviour under an equivalent three-conductor transmission line, a concentric arrangement of the metasurface under the spiral is proposed. This metasurface is designed to absorb the edge reflected waves to improve the circularly polarized response of the antenna below 6 GHz. The antenna substrate with the metasurface is placed above a flat conductor that makes an overall antenna height of 5 mm. After numerical investigations, a prototype is fabricated and characterized. The measured right-hand circularly polarized gain is positive above 2 GHz with a maximum gain of approximately 8.7 dBic at 10.6 GHz. An axial ratio better than 3 dB is observed above 1.125 GHz. The benefits of the metasurface compared to a commercially available absorbing material is highlighted, and its usefulness to design a compact spiral antenna is presented.

This paper proposes an approach to improve the gain of a microstrip patch antenna on a suspended substrate without compromising its bandwidth. The ground plane of the antenna is folded upwards to form sidewalls parallel to the non-radiating edges. The distance from the patch edges and the height of the sidewalls are determined to maximize the radiation performance of the resultant antenna. This approach results in a peak gain better than 12 dBi and impedance bandwidth of around 45 $\%$ . Simulation studies indicate that sidewalls parallel to radiating edges degrade the antenna performance.

Electromagnetic (EM) windows with a digitally reconfigurable metasurface (DRM) are proposed to experimentally demonstrate a multipath based communication technique known as media-based modulation (MBM). In MBM, the magnitude and phase of a transmitted tone from a single RF chain are modulated in space using different switching combinations of DRM. After transmission, superposition of various multipath components helps diversifying the transmitted symbols across the constellation leading to an improved signal-to-noise ratio (SNR), bandwidth, and energy-efficient multiuser system with enhanced security, reduced outage probability in a slow fade channel, and possibility of achieving capacity of a Gaussian channel. Prototype of an 8 $\times$ 8 array of the DRM unit cells with p-i-n diodes for switching and its hardware interface are developed to perform experiments under different scattering environments. Constellations, bit-error-rate (BER) responses, and statistical distributions of the received symbols with the measured data establish the above characteristic features of a wireless link using MBM. A scheme for the data transmission with DRM is also discussed.

Low-profile wideband spiral antennas suffer from poor impedance matching and cross polarization at lower frequencies or high variation in gain at higher frequencies. These significant differences, primarily caused by electromagnetic coupling with a conventional conductive backing, and the resulting interference are addressed in this letter by suitably designing the profile of the conductor. The proposed geometry has a maximum height of 0.08 $\lambda _{m}$ at the minimum operating frequency and has wideband circular polarization performance with a good boresight gain response over 2–18 GHz range. After numerical investigations, a prototype antenna is fabricated and characterized. An excellent impedance matching and circular polarization behavior are measured close to 2 GHz while the variation in gain is limited between 5.8 and 8.6 dBic above 10 GHz.

Electromagnetic (EM) systems are prone to parameter variations and their impact help in predictive analysis. In this letter, proper orthogonal decomposition is proposed as a fast uncertainty quantification method, which can efficiently handle a large number of stochastic parameters, without any restriction on the levels of variations. The performance of the approach is evaluated in a frequency domain stochastic EM problem employing vector finite element method and having permittivity variations. The computational time increases by only 15% even with a fivefold increase in the stochastic variables.