This article presents the design and performance analysis of a printed microstrip ultra-wideband (UWB) antenna consisting of the slots in the ground plane and radiating patch. A meandered S-shaped slot has been introduced on the patch and an inverted U-shaped slot has been incorporated in the ground plane to realize the band-notch effect for WiMAX (3.2–3.8 GHz) and WLAN (5.1–5.8 GHz) bands respectively. The total dimension of the proposed design is 44 × 44 mm2. The fabricated antenna exhibits wide impedance bandwidth of 10 GHz (2.4–12.4 GHz), i.e., 135% of center frequency. The design prototype is fabricated, and the measured results have good agreement with simulated values. The effects of the slots have been analyzed by simulated surface current distribution. The designed antenna shows almost omnidirectional radiation patter and stable gain. The proposed hexagonal antenna may be suitable for UWB applications removing WiMAX and WLAN bands.

This paper furnishes a compact modified hourglass-shaped aperture-coupled antenna for radar applications. The effect of slots of various shapes and various slot lengths on the input impedance, radiation pattern, and gain of the antenna are analyzed. The proposed antenna, designed using a modified hourglass-shaped aperture, offers a gain of 8.214 dBi for an compact antenna with a dimension of 20.4 × 20.4 × 1.041 mm3 and an aperture area of 2.495 mm2. Implementation of this proposed modified hourglass-shaped aperture offers a high gain per unit radiating patch area of 40.26 dB/$\lambda _g ^2$ and a high gain per unit aperture area of 1324.84 dB/$\lambda _g ^2$. The proposed aperture feeds a circular patch which radiates at its resonant frequency of 10.5 GHz. The proposed design is fabricated and the simulated results are verified experimentally. Equivalent circuit analysis is also done. A measured gain of 7.2 dBi is observed at 10.5 GHz. The physical area of the antenna is reduced without compromising the gain by judiciously choosing the shape of slot with more degree of freedom for impedance matching. The proposed antenna is well suited for the unit cell of phased array antennas for X-band missile radar applications.

A novel low-profile two-arm backfire tapered cone helical antenna for telemetry tracking and command (TT&C) is introduced theoretically and experimentally in this paper. Compared with the conventional helical antenna, this design has a substantial decrease in its height and an increase both in its half power beamwidth (HPBW) and 3-dB axial ratio beamwidth by replacing the uniform structure with two tapered cone structures. It provides a maximum gain of 5.1 dBi, an excellent circular polarization radiation over a wide angular range of more than 124°, a 3-dB axial ratio bandwidth of 18.8%, a wide HPBW of more than 125°, and nearly equal E- and H- plane far-field patterns with high degree of axial symmetry over S-band (2–2.3 GHz). These excellent radiation characteristics with an endurable and compact structure make it an attractive candidate for TT&C application in microsatellite system, where the installation envelope and space for antenna are extremely limited.

This research reports a four-port multiple-input-multiple-output (MIMO) antenna designed for 5G-NR band applications including n77: 3.30–4.20 GHz, n78: 3.30–3.80 GHz, and n79: 4.40–5.00 GHz. The proposed design is analyzed in two parts, one single-element asymmetrical fed Calendula flower-shaped antenna and the other four-port modified MIMO antenna with the connected ground. The evolution of the MIMO antenna is studied based on the characteristics and optimized single-element antenna. The measured 5G-NR bandwidth offers a very high matching of impedance for MIMO configuration and higher isolation in the same band. The MIMO antenna offers an average peak gain of 3.51 dBi with a radiation efficiency of more than 90%. The radiation patterns plotted at 3.51, 4.00, 4.50, and 5.00 GHz match with almost omni-directional and dipole patterns in H- and E-radiating planes respectively. The MIMO antenna also records good diversity performance (ECC, DG, CCL, MEG, and TARC) in n77, n78, and n79 5G bands.

Terahertz technologies for non-destructive testing (NDT) are continuing to find their way into the industrial sector in the context of very specific inspection tasks. Part of this development is the capability to adapt terahertz systems in such a way that they can meet the sometimes harsh challenges and requirements of real-world industrial scenarios. One such scenario is the inspection of components with limited available measurement space. In particular, we show here the terahertz NDT inspection of the mica insulation of generator bars of turbogenerators at power plants, where an early on-site detection of defects and cracks in the insulation can be crucial, but where only few centimeters of space between adjacent bars are available. To address this problem, we have developed a measurement system combining a 100 GHz all-electronic terahertz transceiver with a low-loss dielectric waveguide antenna with 90 degree tip. We achieve sub-wavelength image resolution by scanning the waveguide antenna's tip over the surface of the generator bars in a near-field measurement setup. Employing a frequency-modulated continuous wave technique, we obtain depth-resolved, volumetric terahertz images of the objects under test. We discuss here the implementation and performance of the implemented measurement system for terahertz NDT inspection. keywords: terahertz, non-destructive testing, dielectric waveguides, frequency-modulated continuous wave, millimeter waves, power generators

The article is devoted to computer modeling, visualization, and synthesis of a digital antenna array used for transmitting and receiving signals in industrial applications. The paper proposes an iterative method for the amplitude-phase synthesis of an antenna array according to the requirements for the envelope of the side lobes. The proposed method allows to determine the complex amplitudes of the elements of a digital antenna array for any given weight function, based on the theorems of matrix theory. The difference of the method lies in the iterative procedure for choosing the weight function, taking into account the excess level of the side lobes of the digital antenna array. In this regard, in the course of solving the synthesis problem, a weight function was found that leads to the fulfilment of the requirements for radiation patterns and does not lead to a decrease in the directivity coefficient. The signal-to-noise ratio was used as a criterion. For the first time, an analytical expression is given for the formation of a weight function in the course of an iterative process that takes into account the requirements for the envelope of the side lobes. The operability and convergence of the proposed method was confirmed in the course of numerical studies on the example of a digital antenna array. The performed numerical analysis confirmed the effectiveness of the proposed synthesis method.

In this article, a novel double-face logarithmic spiral metamaterial (LSMTM) superstrate-inspired multiple-input multiple-output (MIMO) for fully enhanced circularly polarized (CP) antenna system is examined for 5G wireless communications. This novel double-face LSMTM superstrate acts as a planar concave-concave lens. Initially, the antenna is designed with a circular spiral patch to generate CP radiation in the frequency band of interest. Then, at a height of 6.5 mm (0.606 λo) above the MIMO antenna, which has a 0.8 mm (0.075 λo) edge-to-edge separation, the LSMTM superstrate is employed for isolation, gain, and bandwidth improvement. The proposed superstrate enhances the isolation, gain, and bandwidth of the antenna by about 32 dB, 3.47 dB, and 900 MHz, respectively. In contrast to the conventional technique of verifying operation with a simulated surface current distribution, characteristic mode analysis (CMA) is used to provide a better explanation of the proposed antenna's different modes and the creation of circular polarization. Additionally, the CMA supports the development of an effective technique that can predict whether or not the isolation can be further improved. The simulated results align with the measured results and are well adapted for 5G wireless communication devices.

This article concerns the design of a new quad-band monopole antenna with a specific configuration and reduced size. The antenna design is based on a single step meander-line parasitic structure, parasitic stubs, and double inverted L-shaped defected microstrip structure units on the top side of the substrate, and double rectangular-shaped defected ground structure units along with partial ground plane on the bottom side. This design procedure allows to achieve quad-band characteristics and improve the impedance matching. The fabricated antenna prototype with overall dimensions of (0.24λ0 × 0.17λ0 × 0.013λ0) is operating at 2.55, 3.65, 4.65, and 5.8 GHz with fractional bandwidth about 7.7, 12.84, 9.23, and 12.8%, respectively. The antenna exhibits an omnidirectional and a monopole like radiation patterns in the H- and E-planes, respectively, with suitable gains between 2.1 and 3.75 dBi. The measurement results are in good agreement with simulation values, which indicates that the proposed antenna design is suitable for WiMAX, LTE B7 (2.52–2.75 GHz), Sub-6 GHz 5G (n77) (3.39 – 3.87 GHz), Sub-6 GHz 5G (n78) (4.4–4.86 GHz), and WLAN, LTE B46 (5.1–5.82 GHz) wireless applications.

This research investigates the MIMO antenna by using the Theory of Characteristics Mode (TCM) where 10 modes are subjected in designing. Also, 5 modes are the significant mode and 2 modes correspond to non-significant which defines the operating bandwidth and notched bands. The proposed 2 × 2 MIMO antenna configuration is designed for wideband applications with a size of 0.44 × 0.68 mm2. The two isolated 12-sided polygons radiating patches placed adjacent to each other share a common ground which is printed on an FR4 substrate. The measured impedance bandwidth covers bandwidth 3.11–11.98 GHz with two bands rejecting capability: Wireless Local Area Network (WLAN) and Downlink-Uplink Satellite (DUS) system. These two interfering bands are mitigated by etching a C-type slot on the radiating patch and an inverted U-type slot in the microstrip feed. The simulated and measured results are also compared in the far-field region (Normalized Radiation Efficiency (NRE), Peak Gain (PG), and 2-D/3-D radiation pattern). Proposed MIMO antenna also offers good diversity performance with ECC2×2 < 0.00001, DG2×2 > 9.999 dB, TARC2×2 < −15.0 dB, CCL2×2 < 0.001 b/s/Hz and MEG2×2 ≅ −3.0 dB.

The scattering by the perfectly electric conducting (PEC) half-plane and PEC zero thickness disk placed on parallel planes is considered. The fields are represented in the spectral domain, i.e. in the domain of Fourier transform. The operator equations with respect to the Fourier amplitudes of the scattered field are obtained. The kernel functions of these equations contain poles. After regularization procedure, which is connected with the elimination of the poles, operator equations are converted to the system of singular integral equations. The convergence of the solution is based on the corresponding theorems. The scattered field consists of the plane wave, reflected by the infinite part of the half-plane, cylindrical waves, which appear as a result of scattering by the edge of the half-plane, and spherical waves, which appear as a result of scattering by the disk and multiple re-scattering by the disk-half-plane. The total near-field distribution and far-field patterns of cylindrical waves are presented.

This paper presents a novel decoupling technique for two-element multiple-in multiple-out (MIMO) antennas for smartwatch applications with floating metallic bezel. The radiating elements consist of embedded loop-type ground-radiation antennas and operate at the 2.45 GHz Bluetooth/Wi-Fi bands. An isolator, consisting of a loop-type structure with a lumped capacitor, is attached externally to the ground plane such that wideband isolation between the antennas has been achieved. It is demonstrated that the small-sized isolator is coupled with the large-sized bezel surrounding the ground plane, where the bezel operates as a low-Q decoupler between the antenna elements producing wideband isolation property. Accordingly, optimized results can be obtained by controlling the location of the isolator, the gap between the isolator and the bezel, and the loaded capacitor. Simulation and measured results have been presented to validate the design performance. The measured −10 dB impedance bandwidth of both antenna elements is more than 210 MHz, whereas the isolation bandwidth is 770 MHz with reference to 20 dB. The envelop correlation coefficient is <0.1 in the operating band. Furthermore, the proposed technique is versatile regardless of the angular separation of the antenna elements on the circular ground plane, which makes it a good candidate for smartwatch MIMO applications in practical scenarios.

In this work, the use of a configuration of a reflective metasurface (MS) layer is employed to design a highly directive wideband Fabry–Pérot cavity (FPC) antenna. With the use of only one MS layer and along with the achieved high directivity, the antenna's wide bandwidth, and antenna low size/cavity thickness profile are all optimized so that they are still competitive which is the main contribution of our work. The highly reflective MS layer is placed as a superstrate of a low-cost FR4 microstrip patch antenna, as the primary radiator, at a height of half-wavelength cavity condition. Thanks to the employed MS layer, most of the power is transmitted and a very small reflected power to the primary patch. The antenna is designed to serve the 28 GHz band of 5G wireless applications. At 28 GHz, the FPC antenna has a good directivity performance, with a peak simulated directive gain of 15.46 dB and measured directive gain is 14.3 dB which is a 9 dB enhancement in directivity compared to a conventional microstrip patch antenna. The antenna has a wide impedance bandwidth of 2.9 GHz which is almost three times the microstrip patch antenna bandwidth. The achieved results are for the same size of FPC antenna whose height is almost half wavelength and its overall size 2.33λ × 2.33λ.

In this paper, a light-controlled frequency reconfigurable antenna is presented for 5 G, WLAN, and radio altimeter applications. The given (44 × 28) mm2 antenna consists of a radiating V-shaped structure and three stub arrangements. The main λ/2 length stub is used to feed the antenna and the two λ/4, λ/8 length open-circuited stubs are located perpendicular to the main feeding stub for tuning the frequency of the antenna. The length of the stubs can be adjusted by placing (4 × 1.2) mm photodiode switches on the perpendicular stubs. Four experiments are carried out to analyze the performance of the antenna. When light and DC bias voltage is not applied (Experiment-1) to the photodiodes the proposed antenna radiates from 4.1 to 4.63 GHz with 12% bandwidth. When light is applied to the photodiode without DC bias voltage and DC bias voltage is applied without light (Experiment-2,3) the antenna reconfigures its frequency band from 3.43 to 3.6GHz and 4.8 to 5.4 GHz with 4.85% and 12% bandwidth respectively. The antenna shifts the radiation from 4.8 to 5.5 GHz with 14% bandwidth when the light and DC bias voltage is applied to the antenna(Experiment-4). The measured gain of the proposed antenna is greater than 3.8dBi in all the experiments.

In this work, a compact, wideband, circularly polarized wearable antenna is proposed using asymmetric coplanar strip feeding for wireless health monitor applications in the ISM frequency band. The proposed antenna consists of a composite right/left transmission line (CRLH TL) inspired structure to achieve compactness and a rectangular ring slot is created in the metallic ground to enhance the CP radiation of the antenna. A 5 × 5 artificial magnetic conductor unit cell-based metasurface is designed which is operating at 2.4 GHz as a ground plane for the CRLH-based CP antenna. Implementation of AMC-based metasurface as a ground plane results in enhancement of radiation characteristics of CRLH TL antenna. The proposed antenna has a small footprint of 50 × 50 mm2 with measured impedance bandwidth of 2.3–3.2 GHz. The 3 dB axial ratio bandwidth of the proposed antenna is 2.36–2.78 GHz with peak gain of 5.89 dBi. Simulation and experimental results show that proposed AMC-based antenna is robust in terms of structural deformation. Further, to validate the performance of the antenna for biomedical applications, we have simulated the proposed antenna with human phantom model. The proposed antenna exhibits stable scattering and radiation characteristics with the phantom body environment and due to the inclusion of AMC structure, the proposed design satisfies maximum specific absorption rate value given as per the IEEE standard safety guidelines.

With the evolution of 5G and 6G network architectures, the demand for highly compact system-on-chip-based devices with high data transfer capabilities has been increased significantly. While the advancement of very large-scale integration technology with the continuous scaling of complementary metal–oxide–semiconductor nodes put forward to integrate different functional modules of a complete system on a single IC board, the antenna being the largest component still remains outside of the chip. Integration of the antenna and other functional modules of a system on the same chip leads to produce a really compact and economical design. Though on-chip antenna (OCAs) have several other advantages and emerging applications, they have some design challenges in terms of low gain due to losses in the substrate, requirement of miniaturization at lower microwave frequencies (LMFs) (particularly, below 10 GHz), unavailability of proper design rules, etc. In this paper, analyzing the design challenges of OCAs, their current research trends and future perspective applications are discussed.

Magneto-dielectric antennas (MDAs) provide small sizes, enhanced bandwidths, and frequency/polarization agility. We describe the fabrication and efficiency characterization at 0.4–0.8 GHz of five microstrip MDAs, whose gradually thicker substrates were 3D-printed using an off-the-shelf polylactic acid (PLA) filament doped with ferromagnetic particles. It was experimentally discovered that efficiency increases monotonically from 12% (−9.2 dB) to 37% (−4.3 dB) as substrate thickness goes from 1.6 to 4.3 mm; the rate is faster than expected for microstrip antennas. Numerical analysis indicated that the apparent magnetic loss tangent of the MD substrate experiences a threefold decrease as the 3D printer deposits more layers of iron-doped PLA. The MDAs exhibit radiation quality factors that are 3.7–7.2 times better than the dielectric counterparts. Moreover, a simple optimization of ground plane size could increase efficiency to 55% (−2.6 dB). The reduction in magnetic loss is attributed to a reduction in eddy current loss due to the separation of agglomerate iron particles. Therefore, despite the inherently lossy material used, the potential of 3D-printed MD substrates in providing acceptable antenna efficiencies is demonstrated together with unprecedented design freedom and fabrication flexibility.

An innovative and simple method for attaining broadband frequency reconfigurable antenna structure is presented using low-cost materials and a compact design. The frequency reconfigurability is attained by the “OFF” and “ON” mechanisms of three PIN diodes. Many performance observations are carried out such as reflectance coefficient, bandwidth (BW), resonance frequency, electric field, feed position variation, and gain among different configurations. The suitability of the presented work for the different applications lies in the X frequency band. The resonating frequency for all switch OFF modes is achieved at 13.2 GHz and one switch ON mode at 10.7 GHz. The proposed design yields the frequency tunability behavior over the broadband of 2.5 GHz. The design yields the directivity of 5.58 dB, the minimum reflectance coefficient of −17.27 dB, and a total gain of 3.87 dB. This design offers an electric field of 46 558 v/m, a BW of 340 MHz, and a normalized directivity of 87° using low-cost substrates. The results of the presented design were also fabricated and related to simulated results. Performance observation of the proposed work with previously published research work is also included. The presented design provides the solution of the low-cost, compact, reconfigurable antennas, which can be used for next-generation communication systems.

In this work, a compact size 4 ports multiple input multiple output (MIMO) slot antenna with the connected ground for Ultra-Wide Band (UWB) and X band applications is introduced and discussed. The single antenna is a cross-shaped slot antenna in the ground plane and a 50 Ω microstrip line with a small L-stub is used to feed the antenna on the other side. The suggested MIMO antenna has four identical elements arranged to be orthogonal to each other to enhance the MIMO system performance. The antenna elements are connected with a small strip to compose the proposed connected ground antennas. The suggested MIMO antenna has an overall size of 47 mm × 47 mm. The antenna has tested and simulated bandwidth with S11 < −10 dB extended from 4– 14 GHz and has isolation greater than 20 dB between ports without utilizing the decoupling elements and with good consistency between results. The MIMO antenna has peak gain and efficiency, envelope correlation coefficient, diversity gain, and channel capacity loss of 5.6 dBi and 80%, <5 × 10–3, 10 dB, and <0.4 bit/s/Hz, respectively which prove that our antenna can be suggested for the UWB MIMO applications.

A simple process for the design of broadband planar antennas is presented for base station applications. The process is based on a square patch above a ground plane. Only three geometric parameters are involved in the design of a dual-polarized broadband planar antenna, including the width (Ws) of the square patch, a trimming angle (θ) of the square, and the height (H) of the patch above the ground plane. By adjusting the critical parameters θ and H, an impedance bandwidth of 50% for return loss (RL) >15 dB is achieved with an isolation of higher than 35 dB. The bandwidth of the broadband planar antenna is enhanced to 67% by etching four Γ slots on the square patch. The operating mechanisms of these broadband antennas are analyzed and verified by simulation and experiment.

In the research of the natural ecological environment, environmental scattering is an important research content whose results are widely used. In order to fully study the relevant characteristics of the natural grassland environment, this paper established a grassland broadband clutter model, summarized the dominant and recessive laws of the grassland environment broadband clutter, and provided a new perspective for related environmental monitoring which would be helpful to solve the problem of target detection in complex environments. The main work of this paper is as follows: The dielectric constant model of the grass was established, and the curve of the dielectric constant with frequency was obtained. The Monte Carlo method combined with the Gaussian spectrum function was used to generate a two-dimensional Gaussian surface to simulate the actual grass surface. A broadband clutter model was established, and, considering the calculation efficiency and accuracy, the Sparse Matrix/Canonical Grid (SMCG) was used to calculate the surface scattering coefficient. Then, the environmental clutter amplitude with different radar bandwidth (10, 40, 80 MHz), surface roughness (h = 0.1 m, h = 0.2 m, h = 0.4 m) and grazing angle (30°, 60°) were calculated and the probability density function (PDF) was obtained. The results show that the higher the radar resolution, the larger the incident angle, and the rougher the interface, all of which will cause the tail of the PDF to become longer which will not only reduce the detection probability of the radar, but also the tracking accuracy. The research results can be used for civilian and military field.