This research paper introduces a novel dual-band single-polarized (DBSP) series-fed center-fed open stub (SFCFOS) Binomial Antenna Array synthesis technique to improve side lobe levels (SLL) and better isolation for the use in Airborne Synthetic Aperture Radars (AIR-SARs). The antenna utilizes a shared-aperture array (SAA) architecture, operating in both X and Ku-bands with center frequencies of 9.3 and 13.265 GHz with a frequency ratio of 1:1.426. The SAA consists of a 7-element linear array of square microstrip patches for the X/Ku-band. The inter-element spacing between patches is set at 0.7λ to meet the ±25˚ scan range requirements. The X-band (9.3 GHz) frequency is ideal for soil moisture estimation in agricultural areas, while the Ku-band (13.265 GHz) is suitable for applications in snow-covered regions, cold areas, and disaster monitoring. To validate the antenna design, a prototype is fabricated and tested for S-parameters, radiation characteristics, and gain measurements. The size of the shared-aperture antenna is 200 mm × 50 mm × 0.787 mm. The measured results of the prototype align well with the simulated ones, exhibiting excellent radiation performance and high isolation. The bandwidth of 1.07% (X-band) and 1.5% (Ku-Band) and return loss of 25 dB/-15.7 dB at 9.3/13.265 GHz are achieved. The measured isolation is -45 dB which provides a large signal separation at X/Ku-bands. The antenna design shows a side-lobe level (SLL) of -39.5 dB at E-Plane (φ=0˚) and -17.9 dB for H-plane (φ=90˚) for the X-band and -35 dB at φ=0˚-19 dB for H-plane (φ=90˚) for the Ku-band. Additionally, it achieves high gain values of 12.8 dBi for the X-band and 13.2 dBi for the Ku-band. This research presents the first reported shared-aperture X/Ku-band single polarized planar array with binomial amplitude distribution synthesis technique, which holds significant value for AIR-SAR applications. All the measured results were in line with simulated ones and matched reasonably well.
In plantation areas, soil conditions affect the crop's quality. One of the crucial elements in the soil for plant survival is soil water content (SWC). Radar system has advantages that can be implemented for measuring SWC in plantation areas. A radar system operates by utilizing electromagnetic waves to obtain the dielectric characteristics of the soil. However, the presence of tea plants has become an obstacle to the radar wave propagation toward the soil layer. Reflected signal, which is influenced by the presence of vegetation, makes the estimation of SWC inaccurate. Consequently, the estimation of SWC needs to consider the vegetation's effect. This study uses an FMCW radar system, which operates at a frequency of 24 GHz. A layer medium propagation model is proposed in this study to prove the relationship between the reflected signal and the SWC. The reflection coefficient extracted from the radar signal is used to estimate the SWC. The vegetation propagation constant was obtained from the average field measurement results. The gravimetric method is used to validate the SWC estimation in vegetation's presence using the radar system. The results of the field experiments showed that the proposed method succeeded in estimating the SWC by considering the presence of vegetation with an average error of 3.57%. The proposed method has the potential to be applied to plantation areas.
The article presents a multiband symmetrically placed two elements, inverted-F multiple inputs multiple outputs (MIMO) antenna for wireless LAN (WLAN), Industrial, Society and Medical (ISM) band, S-/C-band applications. Decoupling (S_{12} < -15 dB) between the two antenna elements of MIMO antenna is improved by introducing metallic vias at the top ends of the patch. The MIMO antenna has been fabricated and measured on a piece of low-cost, low-profile, FR-4 substrate. A combination of parasitic loading of 4-units (quadruplet) of square-split ring resonators (SRRs) and complementary split ring resonator (CSRR) cells have been used to achieve quad-bands for lower than -10 dB total active reflection coefficients and additionally to improve isolation between antenna elements. The paper also presents the tabularized and graphical investigations of the analyzed and measured resultant MIMO parameters like; envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficients (TARC), MIMO-VSWR (voltage standing wave ratio), channel capacity loss (CCL), etc. and are found approximately close to each other with small acceptable errors. The other important parameters (reflection coefficients, radiation pattern, E-plane and H-plane polar plots, electric field vector (E) distribution, and current density vector (J) distribution) of the proposed antenna were also demonstrated and measured using a vector network analyzer (Agilent N5247A VNA) and 18 GHz Anechoic chamber in the microwave research laboratory. The MIMO (1×2) antenna is best suitable for Bluetooth/WLAN/Wi-Fi (2.45-2.57 GHz) and ISM band, FIXED, MOBILE, RADIO Location, Amateur & Amateur-satellite service (2.45 GHz) within impedance bandwidth (S_{11} < -10 dB) from 2.45-2.57 GHz lower band, and n46 (5.40-5.49 GHz) upper band.
An efficient method for designing narrow beams having minimum peak side lobe level (PSLL) and maintaining power efficiency (reducing active elements) for 5G/6G base stations with large antenna arrays is proposed. To ensure high efficiency in a multi-dimensional complex nonlinear optimization problem with several constraints thinning of antenna of antenna arrays is considered. For performing exhaustive search on the large number of feasible solutions a novel algorithm named discrete cat swarm optimization (DCSO) is usedand is a binary adaptation of real-valued cat swarm optimization (CSO). To testify the efficiency of DCSO a set of standard benchmarked multimodal functions are used. The proposed algorithmsexhibit heuristic nature, so the stability of the proposed method has been authenticated by using statistical test. Later the algorithm is applied to the optimization of a large planar antenna array (PAA) of size 10×20 (200 elements) to suppress the PSLL. Furthermore, the results of the synthesis are compared with literature marking low PSLL and convergence speed as pointers. The comparative results delineate the superiority of the DCSO over the existing discrete versioned traditional algorithms with respect to solution accuracy and speed of convergence. DCSO introducesa higher degree of flexibility to the field of binary-valued thinned antenna array synthesis problems.
The uniform geometrical theory of diffraction (UTD) calculating edge diffraction, creeping diffraction, and reflection, has been widely used to predict the shadowing problems for the beyond 5th generation. The limitation of the previous work, which only discussed the relationship between edge diffraction and reflection in the lit region, has motivated the analysis of the difference between creeping diffraction and edge diffraction in the shadowed region. In this paper, as the difference between creeping diffraction and edge diffraction from a dielectric circular cylinder and an absorber screen, respectively, a novel additional term is derived based on the UTD in the shadowed region. In addition, a uniform additional term using the Fock-type integral is proposed to unify the formulations in the lit and shadowed regions. The proposed uniform additional term is validated by the UTD and exact solutions of a dielectric circular cylinder at millimeter-wave or sub-terahertz bands. From the discussion of the results, the proposal can not only unify the formulations in the lit and shadowed regions but also eliminate the fictitious interference. Through the proposal, we can separate the contribution of the shadowed Fresnel zone number (FZ) and boundary conditions (i.e., the surface impedance and polarization). The frequency characteristics of the shadowed FZ and boundary conditions are analyzed and simulated near a shadow boundary at a high frequency (10 GHz-100 GHz). The results imply that there is almost no dependency (less than 1 dB) on boundary conditions in the lit region while there are few dependencies (more than 1 dB) on boundary conditions in the shadowed region. This work attempts to unify three different propagation mechanisms, i.e., reflection, edge diffraction, and creeping diffraction, by using one formula.
Dynamic Inductive Wireless Power Transfer (DIWPT), used for charging and powering electric vehicles (EVs), has been presented lately as a solution for increasing the distance range of electric vehicles and reducing the utilization of heavy and bulky battery systems. In most DIWPT designs, the voltage induced by the movement of the receiving coil over a time-varying magnetic field is neglected and never quantified. In this work, a simplified phasor expression for the total induced voltage on a coil that is moving in a sinusoidal time-variant magnetic vector field is developed. If no rotation is observed in the coil, a 90˚ out of phase voltage component proportional to the speed of the coil is added to the induced voltage that would be calculated if the coil was stationary. The phase of this voltage component is delayed or advanced with respect to the stationary induced voltage, according to whether the coil is moving into or out of a region of higher magnetic flux. Then, under some assumptions on the geometry of inductive coil configurations, it is possible to estimate the minimum induction frequency for which the quasi-stationary approximation can be considered. The resulting frequency value for a representative geometry is calculated, indicating that, for automotive applications, the relative error in the induced voltage is actually negligible, except in the vicinity of the points of zero-crossing in the magnetic flux, where the absolute value of the induced voltage is low anyway.
This paper presents an in-depth review of the performance improvement of antennas using metasurface. Metasurface is a periodic arrangement of perfect electric conductors (PECs) on a metal-backed dielectric substrate that do not exist in nature and are able to manipulate the behavior of electromagnetic (EM) waves incident on it. The manipulations of EM waves improve the performances in terms of impedance bandwidth, gain, size, specific absorption rate (SAR), radar-cross-section (RCS), and polarization conversions. Consequently, numerous recent works on metasurface-inspired antenna design and their theoretical perspectives on performance enhancements are discussed. By adopting the discussed theories, novel metasurfaces are developed and proposed that analyze impedance-bandwidth enhancement, gain enhancement and SAR reduction. For designing the metasurfaces, initially a conventional rectangular unit cell (CRUC) is theoretically developed using transmission line model at 2.45 GHz. Following that, the CRUC-based metasurface is incorporated with a monopole antenna, which enhanced the impedance-bandwidth from 140 MHz to 320 MHz and the gain from 2.5 dB to 7.4 dB. On the body, the presence of the metasurface retains all the performances as free space, with a reduced 1 g SAR of 0.034 and 10 g SAR of 0.024 W/Kg.
In this paper, a novel frock shaped four-port MIMO antenna is designed, and experimental results were verified for UWB applications. The four elements are placed orthogonal to each other to reduce mutual coupling. The proposed novel-shaped antenna is derived from a circular patch antenna. A series of modifications were made on a circular patch antenna to get desired single novelly shaped radiator. Inserting decoupling stubs in the Plus form between MIMO elements lessened mutual coupling. The entire designing procedure of the proposed four-port antenna was carried out by Characteristic Mode Analysis. The proposed model is printed on an Fr-4 substrate with dimensions of 40x40x1.6 mm^{3}. This novel 4-port antenna is well-operated in the UWB range from 2.8 GHz to 11.4 GHz and bandwidth of 8.6 GHz. The novel shape radiators with good decoupling stubs produce a high impedance bandwidth of as 121.8%, radiation efficiency of 91%, high isolation 26 dB, and a gain of 6 dB in the operating band. The diversity parameters are enveloped correlation coefficient (ECC) less than 0.0011, diversity gain (DG) very near 10 dB, capacity channel loss of 0.28 bp/s/Hz, and mean effective gain of -3.1 dB. The experimental results of the antenna are verified with simulated ones and got good agreement between fabricated and simulated results.
This paper presents a stabilized scheme that solves the wave propagation problem in a general bianisotropic, stratified medium. The method utilizes the concept of propagators, i.e., the wave propagation operators that map the total tangential electric and magnetic fields from one plane in the slab to another. The scheme transforms the propagator approach into a scattering matrix form, where a spectral decomposition of the propagator enables separation of the exponentially growing and decaying terms in order to obtain a well-conditioned formulation. Multilayer structures can be handled in a stable manner using the dissipative property of the Redheffer star product for cascading scattering matrices. The reflection and transmission dyadics for a general bianisotropic medium with an isotropic half space on both sides of the slab are presented in a coordinate-independent dyadic notation, as well as the reflection dyadic for a bianisotropic slab with perfect electric conductor backing (PEC). Several numerical examples that illustrate the performance of the stabilized algorithm are presented.
In this article, a planar compact grounded coplanar waveguide (GCPW)-fed 4-element multiple-input multiple-output (MIMO) antenna array with a defected ground structure (DGS) is demonstrated for fifth generation (5G) millimeter-wave (mmWave) communication. Each element of GCPW-fed mmWave MIMO antenna array contains a deformed pentagon-shaped radiating patch etched with a pair of identical circular slots in top surface and a DGS in bottom surface. To maintain low design complexity and compactness, a DGS is introduced and formed by embedding dual asymmetrical inverted T-shaped slots in the partial ground plane which enhance the gain and bandwidth of the antenna. The equivalent circuit model of the proposed DGS loaded GCPW-fed antenna is realized and presented. The proposed 4-element mmWave MIMO antenna array is realized by arranging the 4 identical antenna elements horizontally in a row with a distinct gap without any decoupling structure. It has the size of 1.02λ × 3.86λ × 0.021λ (at 25.66 GHz) and exhibits the measured bandwidth of 49.62% (25.30-42.0 GHz) with a peak gain of 12.02 dBi. Furthermore, the envelope correlation coefficient (ECC) < 0.0014, isolation > 24 dB between antenna elements, and channel capacity loss (CCL) < 0.29 bits/sec/Hz of the mmWave MIMO antenna array are attained over the entire mmWave frequency band.