In this paper, a compact unidirectional antenna consisting of a planar electric dipole and a shortened connecting element is introduced. This antenna is excited by a Γ-shaped feeding line. A wide impedance bandwidth in the frequency range of 1.3–3.3 GHz is observed in the output performance. Sufficient main lobe and low level back lobe have been introduced as other characteristics of the structure, based on radiation patterns. The antenna design process is evaluated step-by-step and using parametric study based on the antenna geometry. One of the main features of the desired antenna is the realization of circular polarization in a high percentage of the operational bandwidth 1.5–3.3 GHz. The radiation patterns of the orthogonal planes E-field and H-field along with the left-handed and right-handed circular polarization patterns for the desired antenna have been extracted and analyzed. A three-dimensional structure in the form of stacked stepped disks (SSD) is introduced to increase overall performance of antenna. There is an acceptable similarity between the E-field and H-field page patterns, which shows the accuracy of the design process. On the other hand, for studying the circular polarization, left-handed and right-handed patterns based on the main beam direction and orthogonal polarization level have acceptable performance. The maximum overall gain of the antenna in the designed frequency band is near to 13 dB.

The microwave energy-harvesting (MEH) and microwave power transfer (MPT) technologies have become the most emerging areas of research nowadays. The microwave rectifier circuit is the bottleneck of both the MEH and MPT systems. The efficiency of the system depends on the power conversion efficiency (PCE) of the rectifier. Due to the recent advancement of the fifth-generation communication system, it is desirable to propose an efficient rectifier operating at sub-6 GHz 5G bands. A dual-band rectifier circuit is designed and demonstrated for MEH/MPT purposes, specifically at sub-6 GHz 5G frequency bands. The dual-band matching is achieved by using a stepped impedance transmission line. The rectifier covers N78 (3.3–3.6 GHz) and N79 (4.8–5.0 GHz) bands. Peak PCE of 67.6% @ 3.5 GHz and 56.8% @ 4.9 GHz are achieved. For validation purpose, the rectifier is fabricated and characterized and measured results show good agreement with simulated results.

In order to solve the problems of low power transfer efficiency (PTE) and limited distance in magnetic coupling resonant wireless power transfer (MCR-WPT) technology. In this paper, based on the magnetic field control ability of metamaterials (MMs), the way to improve the performance of MCR-WPT systems is studied. First, the influence of MMs on the coupling of MCR-WPT system is theoretically analyzed by establishing an equivalent circuit model. Through a series of simulations and experiments, the relationships between the PTE and the array and placement of the MM slab are investigated. The results demonstrate that when one MM slab is placed in the middle, near the Tx coil or the Rx coil, the optimal PTE can be obtained by inserting one slab with $6 \times 6$, $1 \times 1$, and $6 \times 6$ arrays, respectively. Moreover, the systems with multilayer MM slabs are also studied. The measured PTEs on one, two, and three layers of MM slabs can increase by 20.6%, 29.3%, and 22.6%, respectively. The efficiency improvement capability of one MM slab is better than three slabs but worse than two slabs. This paper discusses the application of MMs in MCR-WPT systems, which has a certain reference significance.

The advancement in wireless communication is fueling the growth of innovative antenna array designs toward cost-effective and performance-oriented solutions. This paper proposed unconventional methods to design antenna arrays for multi-pattern synthesis without using attenuators or phase shifters. A low-cost alternative is proposed with “Time-modulation”-based antenna array capable of electronic scanning and beam steering. Here, “Time” is utilized as a fourth-dimensional (4D) array parameter, and that is why “Time-modulated” arrays are also called as 4D antenna arrays. The idea is to control the high-speed switch attached with each antenna periodically to produce desirable current and phase tapering. This article expanded the “Time-modulation” concept to synthesize multiple radiation patterns like monopulse patterns, scanned beam patterns, shaped beam patterns, and cosecant-squared beam patterns for multifunctional radar systems. Suitable time schemes are developed to generate the narrowband sum–difference patterns useful for monopulse radars. Simultaneous scanned beam patterns are also proposed for narrowband communication. Furthermore, to address the wideband applications, shaped flat-top beam patterns and cosecant-squared beam patterns are also proposed. In this regard, 20- and 16-element “Time-modulated” linear array antennas are developed, and the parameters of the arrays are controlled by suitably designed objective functions with quasi-Newton method (QNM)-based memetic optimization method. For this purpose, first a well-known genetic algorithm is adopted to search the potential trust regions in the exploration stage and QNM is used for fine-tuning. Furthermore, the Broyden’s good method-based direction-updating equation is used with QNM to improve the performance.

We present the design for a thin planar microwave absorber depicting near unity absorption over a wide bandwidth. The absorber consists of a single layer of resistive frequency selective surface inkjet printed over a paper substrate and suspended over a grounded foam. We have been able to achieve 99.99% absorption of normally incident radiations from 9.7 to 11.74 GHz at an extremely low level of −40 dB absorption bandwidth. The proposed absorber is thin (0.22λ0 at the center frequency), polarization-insensitive, and presents −10, −20, −30, and −40 dB fractional bandwidths as 89.83%, 55.41%, 33.30%, and 19.03%, respectively. It is worth mentioning that the design of an absorber with such steep slopes is highly stringent and requires special attention. Finally, we have experimentally demonstrated the perfect broadband absorption characteristics with a fabricated prototype.

In this paper, a compact two-element reconfigurable multiple-input multiple-output (MIMO) antenna for 5G new radio sub-6 GHz is presented and discussed. The proposed MIMO antenna has four frequency operating modes: a wideband operating mode (2.41–6 GHz), a wideband operating mode with a notching band at 3.5 GHz (3.2–3.66 GHz), a low-pass filter mode that filters the higher frequencies with a wide operating band from 2.41 GHz to 4.7 GHz, and a dual-band mode with two operating narrow bands (2.41–3.16 GHz and 3.64–4.7 GHz). To improve the isolation over the entire operating band, a strip line connecting the two ground planes of the two antenna elements has been used. To validate the proposed approach, different prototypes have been fabricated and measured. The simulation results are in good agreement with the measurement results. The proposed antenna has good MIMO diversity performance with a maximum gain of 4.64 dBi. The minimum isolation is 18 dB for the four operating modes, while a measured envelope correlation coefficient of less than 0.008 is achieved. The diversity gain is near 10 dB for various operating modes. The antenna is suitable for cognitive radio and 5G sub-6 GHz applications.

In this article, an angle-independent wideband metamaterial microwave absorber (MMA) for C (4–8 GHz) and X (8–12 GHz) band frequency is presented. The unit cell of the proposed MMA consists of outer and inner structure associated with lumped resistors. The outer structure consists of rectangular split-ring resonator, whereas the inner structure consists of circular split-ring resonator. The structure is made up of three layers, in which top and bottom layers are made up of copper acting as a conducting material. The middle layer is made up of FR-4 acting as a dielectric substrate. The resonating structure at the top is designed in such a way that wideband absorption is achieved in the range from 6.11 to 13.52 GHz. The wideband absorption within the range approaches almost unity having a bandwidth of 7.41 GHz. Three different peaks are considered in the range of interest having maximum absorption of 0.94, 0.94, and 0.99 at frequencies of 6.76, 11.15, and 13.07 GHz, respectively. The structure is analyzed with respect to the effective parameters, i.e., effective permittivity (${\varepsilon _{{\textrm{eff}}}}$) and effective permeability (${\mu _{{\textrm{eff}}}}$), to prove that the structure acts as a metamaterial. Electric field and current distribution are plotted at three different peaks to prove the mechanism of wideband absorption. Normal and oblique incidence are plotted to determine that the structure is behaving as an angle independent. The simulated structure is fabricated on FR-4 substrate and measured inside an anechoic chamber. Finally, to prove the novelty of the work, the proposed structure is compared with the already reported MMA. The proposed MMA finds practical applications in radar cross section reduction, terrestrial communication, keyless entry system, space communication, radar, and baby monitor.

A metasurface reflector-backed wideband planar antenna is designed for millimeter-wave (mmWave) applications. A simple meandering structure is used for radiation element design, while the back side consists of a partial ground plane and parasitic elements. The utilization of meander-shaped element led to small antenna dimensions. The partial ground plane is used to achieve wide bandwidth, while the parasitic elements are used to improve the impedance matching toward higher frequency bands. To achieve high gain and directional radiation characteristics, an array of metasurfaces is placed behind the radiating element. It is observed from the simulated results that the proposed antenna system offers 17.72 GHz of impedance bandwidth in the operating range of 22.28–40 GHz, while the measured impedance bandwidth is noted to be 15.8 GHz, ranging from 23 to 38.8 GHz. Furthermore, it is observed that a metasurface-based planar antenna tends to achieve a peak gain of ≈9 dBi in the band of interest.

This paper investigates the electromagnetic scattering characteristics in arid zone and proposes methods for monitoring and improving ecological agriculture, vegetation landscape and desertification in arid zone, based on the modified small slope approximation (SSA) electromagnetic scattering model. The dielectric properties of dryland soils are studied in the paper, and the variation curves of soil dielectric constant with humidity and electromagnetic frequency are plotted. In order to reproduce the geomorphological features of the dryland areas, a two-dimensional geometric model of the ground environment is established using Monte Carlo methods combined with Gaussian spectral functions. An algorithm model based on the modified SSA is developed, and the algorithm was validated and analyzed to verify its reliability. In the simulations, the southeastern region of Ejina Banner, Inner Mongolia was taken as a typical arid region, and the simulation parameters are obtained from the actual measurement data of the region. The study finds that the electromagnetic scattering characteristics of the arid zone are influenced by soil water content, ground roughness and incident wave electromagnetic frequency, and there is regularity. The results of this paper can be effectively combined with remote sensing technology to contribute to many researches on soil moisture inversion and ecological condition of vegetation, which are important in many aspects such as irrigation control, ecological research, vorticity covariance, and climatology of slope stability.

The increasing demand for wireless communication has emphasized the need for multiband antennas. This study presents a novel design for a multiband antenna with reduced specific absorption rate (SAR), high gain, and improved front-to-back ratio (FBR) achieved through the integration with a 4 × 4 artificial magnetic conductor (AMC) surface. The proposed antenna covers a wide range of wireless frequency bands, including Industrial, Scientific, and Medical, Wireless Local Area Network, Worldwide Interoperability for Microwave Access, Wi-Fi 6E, and 7, with resonating frequencies at 2.4, 3.2, 5.5, 7.5, and 10 GHz. The AMC unit cell creates four zero-degree reflection phases with double negative properties at 2.5, 3.8, 5.5, and 7.5 GHz. The compact design measures 0.23λ0 × 0.296λ0 × 0.0128λ0 and placed 0.104λ0 above an AMC surface of size 0.512λ0 × 0.512λ0 × 0.1296λ0. This structure enhances the gain by up to 8.55dBi at 6.01 GHz. The proposed antenna has −10 dB impedance bandwidth for these corresponding frequencies viz 2.34–2.43 GHz (3.77%), 2.81–3.83 GHz (30.72%), 4.82–6.21 GHz (25.20%), 7–7.65 GHz (8.87%), and 8.06–10.31 GHz (24.5%). An overall average percentage reduction value of SAR taken at these frequencies has been found to be 96.11% with AMC structure. The antenna sample was successfully fabricated, and the experimental results have been found to match well with the simulation results. This integrated design offers a promising solution for wearable off-body communication devices.

This paper proposes a passive filtering antenna for ultra-wideband (UWB) applications. The edge chamfering technique is adopted to construct the UWB antenna. The designed UWB antenna has a fractional bandwidth of 135%. A low-pass filter (LPF) is embedded on the feed line of the UWB antenna to convert it into a narrowband antenna that works at 2.45 GHz with 29.5% fractional bandwidth by removing the high-frequency components. The LPF is a transmission line with a stepped impedance configuration loaded with an H-shaped unit cell. The proposed filtering antenna is fabricated and tested. The measured results indicate the gain is >4.2 dBi and the radiation efficiency is >75%.

The presence of obstacles in the propagation path is a critical factor in air-to-ground (AG) communication. The behavior of wireless signal propagation depends on several variables, such as frequency, building height, elevation angle, and street design. This paper aims to compare the three established line of sight (LOS) probability model based on actual site data, including the building geometry in suburban environment. The comparison between these three models using the site data provide a guideline for selecting the LOS probability model based on the optimistic and pessimistic predictions. The shadowing loss was evaluated at frequencies 2 and 3.5 GHz with an elevation angle of 20° in two suburban locations at Universiti Tun Hussein Onn Malaysia. Three prediction models, ITU-R P.1410-5, Holis and Pechac, and Pang et al., available in the literature were used to identify and compare the line-of-sight probability. By focusing on the shadowing model in suburban area, the guideline for optimizing LOS communications or navigation in these challenging environments can be developed. The finding highlights the importance of considering building height in AG communication for network performance evaluation and design.

In this article, the cylindrical conformation of a linearly polarized cavity-backed magnetoelectric (ME) antenna is studied. Starting from a planar ME antenna presenting a wide bandwidth due to a specific design of its feeding probe, the impact of conformation is shown; the coupling between the ME dipole and the cavity walls is demonstrated to be the key element to keep a wideband behavior. Conformal antennas offering the same impedance bandwidth as the planar antenna are presented operating at Global Navigation Satellite System frequencies (1.164–1.61 GHz). As a result of the conformation, the antenna size has to be reduced to maintain the coupling and a wideband behavior. A prototype conformed to a 44-mm radius cylinder was built using low-cost additive manufacturing. External dimensions of 62 × 62 × 35 mm3 (0.285 × 0.285 × 0.16λ03, where λ0 is the wavelength at 1.38 GHz) were obtained, showing a ground plane area reduction of 46% compared to the planar antenna with the same materials. The conformal antenna also exhibits very steady radiation properties with a gain of around 4.5 dBi and a very similar and stable 3 dB beamwidth around 113° in E- and H-planes. A relatively good agreement is found between measurements and simulation.

This manuscript presents a 50 Ω microstrip-fed quad-element high isolated ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with band-notched characteristics. The overall area of the proposed structure is 0.33λo × 0.33λo mm2 (where λo depicts the free space wavelength corresponding to the lower cutoff frequency, i.e. 2.54 GHz), etched on an FR-4 substrate of thickness 0.8 mm. The top layer has four semicircular disc-shaped radiating elements that are identical and orthogonal to obtain better inter-element isolation and compactness. A reverse two-shaped slot is etched onto the radiating patches to attain a band-rejection capability. Moreover, a decoupling structure is also placed at the top layer to suppress the unwanted surface waves. The bottom layer consists of a ground plane, which is further modified with quasi-self complementary and meandered line slots. A rectangular slot is also etched below the feed line to better match the impedance near the lower cutoff frequencies. The simulated reflection coefficients (S11) of the proposed antenna are less than −10 dB over 2.54 to 10.74 GHz frequencies except at 3.37 to 4.15 GHz (WiMAX/C band), and the simulated inter-port isolation (S21) is greater than −15 dB over the entire UWB range of frequencies (3.1 to 10.6 GHz). Also, the measured S-parameter results well agreed with the simulated ones. Furthermore, the simulation study of the 20-element UWB-MIMO antenna is also investigated using the proposed quad-element structure.

For future fifth-generation (5G) smartphones, a high-efficiency multiple-input/multiple-output (MIMO) antenna system capable of operating in Long Term Evolution (LTE) 42/43/46 is suggested. A pair of small microstrip-fed slot antenna and inverted F antenna is part of the single antenna design structure. They are positioned on the longer side of the FR-4 printed circuit board. In an effort to lessen the mutual coupling, two antenna elements have a U-shaped rectangular slot inserted between them. The detailed study of the suggested MIMO system includes measurement of the reflection parameter, analyzing the radiation performance, performing envelope correlation coefficient (ECC) and channel capacity calculations, and analyses of the effects of user’s hand in the vicinity of the antenna array. Simulation and measurement results demonstrate the required performance of the proposed design, that is, greater than 80% of total efficiency, isolation >12 dB, and ECC <0.15. The suggested antenna has the benefits of multiband operation, high efficiency, good isolation, and a small footprint.

A compact 12-element multiple-input multiple-output loop antenna array for a fifth-generation (5G) mobile phone is proposed. The operating band for the proposed antenna covers the long-term evolution 42 band, which spans a frequency range of 3.4–3.6 GHz. The size of the single antenna element is 5.85 × 4.9 mm2 (0.068λ0 × 0.057λ0), and 12 of these elements are positioned along two side edges of the mobile phone. This antenna is suitable for high screen-to-body ratio devices. The measured 6-dB impedance bandwidth is from 3.4 to 3.73 GHz. The measured total efficiency of the proposed antenna is 39–56% and the peak gain is 0–3.2 dBi. The transmission coefficient is less than −12 dB, the envelope correlation coefficient is less than 0.42, and the channel capacity is 45–50 bps/Hz.

An intra-band pattern-corrected decoupling vertical conducting wall is realized by dielectric substrate with conductor cladding on both side wall between two tightly spaced H-plane microstrip patches with λ0/20 edge-to-edge spacing. The wall is grounded and two symmetrical slots are etched on the vertical substrate. The measured results agree with the simulations, showing that the slotted vertical wall reduces the mutual coupling within the bandwidth to −30 dB and corrects the radiation beam tilt to be within −4.5° to 3° from the broadside direction. A gain reduction of 0.6 dB is observed compared to the gain without the slotted decoupling wall.

For forthcoming wireless applications, a small and highly decoupled complementary split ring resonators (CSRR)–loaded co-planar waveguide (CPW)–fed antenna for dual-band applications is investigated. The low-profile antenna consists of a CSRR-loaded rectangular radiating element with a truncated bottom, giving a wideband performance over the frequency ranges of 5.28–5.52 GHz and 6–7.2 GHz. The antenna has been printed on a widely used FR4 substrate measuring 7.5 × 10.5 × 1.6 mm3 in volume. This research’s suggested antenna is turned into a 4 × 4 multi input multi output (MIMO) construction using a 25 × 25 mm2 printed circuit board. Individual antennas were isolated by nearly 20 dB without using a decoupling device. The antenna has been built, and the measured and simulated results correspond well. Computing envelope correlation coefficient (ECC), channel capacity (CC), and channel capacity loss (CCL) further validates the antenna’s performance (−). The antenna has an overall gain of around 2.54 dBi and a radiation efficiency of approximately 89% throughout the relevant spectral range, which is much better for wireless applications. The suggested antenna’s omnidirectional emission pattern makes it a potential contender for future wireless and cellular applications.