A pattern reconfigurable microstrip patch antenna with two parallel parasitic patches placed close to both sides of a rectangular driven patch is investigated and presented in this article. Four switchable shorting posts are used to enable the parasitic elements to act either as a reflector or director for beam reconfiguration, based on the operating state of four associated PIN diode switches. To avoid large change in the dimension of both parasitic patch and ground plane, and minimize its effect on beam steerability and return loss, two PIN diodes are placed on the top face and the other two on the slots etched on the ground plane. Radiation pattern of the proposed antenna can be reconfigured into four distinct directions in the H-plane with radiation maximum at +40˚, 0˚, -40˚ and ±45˚. With overall compact dimension of (35×55) mm² and acceptable return loss for all reconfigurable modes around 6.2 GHz frequency, the proposed antenna is a potential candidate for Wi-Fi 6E application. The measured peak gain varies between 3.9 dBi and 5.2 dBi with an average of 4.6 dBi for all beam tilt angles. Consistency between the simulated and experimental results validates the design theory and its promising application.

A compact and hexagon-shaped microstrip patch antenna operating in three bands is described in this paper. Multiband functionality of the antenna is achieved by adding two inclined strips and cutting modified slots on the radiating patch. The antenna consists of a hexagonal patch and partial ground plane, has the total dimensions of 15×17 ×1.6 mm³, operates over three frequencies 5.40 GHz, 6.76 GHz, and 8.82 GHz for WLAN, TV satellite broadcasting, WiMAX (5250-5850 MHz), IEEE 802.11a (5.47-5.725 GHz), 5G Unlicensed band (5.2-5.7 GHz), weather monitoring, and radar applications. This antenna has the novelty that it can also be used as a reconfigurable antenna, and the notched bands can be controlled. Simulation of the proposed antenna is carried out using HFSS-15 software. To verify the simulated results, and a prototype of the proposed antenna is fabricated. After measurement, simulated and measured results are in good agreement.

In this article, a slot-antenna array with wideband and high-isolation for multiple-input multiple-output (MIMO) systems is presented that can be used in fifth-generation new radio (5G NR) communication. The MIMO antenna system is realized by loading six identical antennas (Ant1-Ant6) into an FR4 substrate to form a six-port array for a 6×6 MIMO system. Each antenna element is a slot antenna type that is composed of a T-shaped open slot and an L-shaped 50 Ω microstrip line. Each T-shaped slot is formed by inserting an I-shaped open branch in the center of the ground plane's U-shaped slot. The L-shaped microstrip line is placed on the upper surface of FR4 to enable coupling feeding in the 3.3 to 5.10 GHz frequency range to cover the 5G NR bands N77/N78/N79. The isolation is increased to more than 18.1 dB by etching the T-shaped slot between the radiation elements on the metal plate. The proposed antenna system was fabricated and tested. The experimental results indicate that the MIMO system can cover the frequency range of 3.20-5.15 GHz with a return loss of 6 dB and provides isolation greater than 16.2 dB. Additionally, a total efficiency greater than 50% and envelope correlation coefficient of less than 0.02 are obtained. The performance under hand-on scenarios is also good. Simulated and measured results indicate that the stated results are consistent. The test results indicate that the antenna satisfies the 5G communication requirements.

This paper presents a triple band proximity fed 2x1 array antenna with defected ground plane. The proposed antenna configuration is composed of two radiating elements, and both radiating elements are made of a pattern similar to the first iteration level David fractal geometry. The proposed David fractal 2x1 array antenna is designed and simulated on an FR-4 substrate of thickness 1.6 mm and dielectric constant 4.3 by using the CST Microwave Studio simulation tool. In order to improve the radiation characteristics of the antenna an H-shaped defect is etched in the ground plane. The antenna is fabricated and tested. The experimental data show good agreements with simulation results. The fabricated triple band fractal 2x1 array antenna resonates at 2.527 GHz, 3.329 GHz and 3.742 GHz having bandwidths of 303 MHz, 99 MHz, and 102 MHz, respectively. The proposed fractal array antenna can be used in mobile applications such as Wi-Fi, WLAN, Bluetooth and Wi-Max.

In this manuscript, a modified spokes wheel shaped two port MIMO (Multi-Input-Multi-Output) antenna with stub loaded ground plane has been presented and experimentally analysed for multiband and EU (European Union) 5900 to 6400 MHz for future 5G mobile terminal applications. The proposed MIMO antenna consists of two radiating patches, and its ground plane is modified to achieve the multiband characteristics as well as enhanced isolation. Initially, a rectangular notch, at the center of ground plane (Ground-1), is employed and reveals four resonant points. Further, the ground plane is modified again by employing two inverted L-shaped stubs along with a series of horizontal rectangular stubs (Ground-2) for enhancing the isolation and reducing the mutual coupling between the elements of proposed MIMO antenna. The antenna with ground-2 exhibits seven frequency bands (S₁₁ ≤ -10 dB) 2.2, 6.0, 7.9, 9.6, 11.1, 12.7, and 15.6 GHz with corresponding isolation (S_12/21) -19.47, -31.22, -34.63, -30.05, -27.16, -39.08, and -22.28 dB. Diversity performance parameters of the proposed MIMO antenna such as ECC, DG, CCL, TARC, and MEG are also in acceptable limits at each operational frequency band. The proposed MIMO antenna is designed and fabricated on a low cost FR4 glass epoxy substrate, and the simulations are carried out by using FEM based Ansys HFSS V13 simulator. Simulated and measured results are compared and found in good agreement with each other.

This article presents a new Butler matrix made on stacked Printed Circuit Boards (PCBs). The matrix is based on Substrate Integrated Waveguides (SIW) and microstrip lines. Transitions using through metallic vias are designed and optimized for the crossover sections of the matrix. The other components of the circuit are as follows: 3-dB SIW directional coupler, 45° phase-shifter, and SIW dual-slot linear antenna array. Different sections of the matrix were simulated, fabricated, and tested. Using the full structure with radiating elements, we obtained good numerical and experimental results in terms of radiations patterns for the different beam directions, impedance matching, and isolation between the input ports.

This paper presents the design of a novel aperture coupled cylindrical dielectric resonator antenna with linear polarization and circular polarization. The linearly polarized cylindrical dielectric resonator antenna (LP CDRA) with proposed aperture and microstrip feed line excites three hybrid radiating modes (HEM₁₁₁, HEM_21δ and HEM_13δ) in three impedance bands. The circularly polarized cylindrical dielectric resonator antenna (CP CDRA) with proposed aperture and flag shaped feed line excites six different hybrid radiation modes (HEM_11δ, HEM_21δ−like, HEM_21δ, HEM_12δ, HEM_13δ, HEM_14δ) in three impedance band and three CP bands. Different sense of CP is reported. The antennas operate in both C and X bands.

In this paper, a dual-model based adaptive sampling method is proposed for the fast calculation of broadband electromagnetic scattering. The difference between the rational function model (RFM) and cubic-spline (CS) based polynomial model issued to generate new frequency samples adaptively. Then, the cubic Hermite interpolation is used to approximate the final broadband RCS curve. The radar cross section (RCS) at each frequency sample is computed by the method of moment (MoM) which is accelerated by the adaptive cross approximation (ACA). Numerical results demonstrate that the proposed method is able to obtain the broadband RCS curve with high accuracy and reduce the computation time significantly. Compared with the method of moment and adaptive cross approximation method, the adaptive algorithm improves the computational efficiency by 77.13% in the sphere case, 83.79% in the rail model and nearly 90.72% in the missile example. In addition, the method proposed in this paper has the characteristics of nonuniform sampling and strong applicability and flexibility, which is able to combine other matrix compressed methods to effectively solve problems in electromagnetic field.

A four-stage switched beam antenna array at millimeter-wave (mm-wave) frequencies is designed, fabricated, and experimental results are demonstrated. A novel rectangular loop dipole antenna (RLDA) applying the quasi Yagi-Uda concept is designed to achieve high gain and wide bandwidth with end-fire radiation. This RLDA with director has a return loss better than 10 dB over a frequency range of 32 GHz to 37 GHz and a peak gain of 8.5 dB. The proposed high gain end-fire RLDA antenna in combination with a 4x4 Butler Matrix(BM) creates the switched beam configuration and generates four beams in the directions of 15˚±2˚, -45˚±4˚, 38˚±2˚, and -15˚±1˚ at 33.5 GHz, 34.5 GHz, and 35.5 GHz with successive input port excitation. The switched beam configuration has overall dimensions at 34.5 GHz is 26 mm x 25.8 mm (3.03λ x 3.0λ).

This paper reports the investigation of a one-dimensional (1D) photonic crystal (PhC) sensor with improved performance for detecting different categories of cancer cells. The sensing region consists of a vertical slot (VS) introduced inside the periodic Bragg mirror. The structure operating principle is based on the change of the refractive index (RI) of the analyte incorporated in the VS, which leads to the shift in the resonant wavelength peak. The sensing properties have been numerically simulated and analyzed using the transfer matrix method (TMM). The study shows that the optimization process of the structure tends to enhance sensitivity. From the result of the numerical simulation, it is found that the final optimized sensor exhibits the higher sensitivity of 3201 nm/RIU than other similar devices. We believe that the obtained results will be valuable for designing highly sensitive PhC sensors.

A novel two-element UWB-MIMO ground antenna is designed by using the theory of characteristic modes. The proposed antenna has a simple and compact coplanar structure, which consists of a rectangular metal ground, a four-stage stepped patch, a double L-shaped patch with a corner cut and a rectangular substrate. By analyzing the most relevant characteristic modes of the metal ground in UWB, the expected characteristic modes are excited by the capacitive coupling elements and the hybrid loading of the capacitive and inductive coupling elements, so as to reduce the size, broaden the bandwidth and improve the isolation. The simulated and measured results show that the proposed antenna obtains ultra-wide impedance bandwidths (2.7-12.6 GHz for Port 1 and 3.0-11.0 GHz for Port 2). Furthermore, the proposed antenna also achieves high gains (3.1-7.3 dBi for Port 1 and 2.7-5.8 dBi for Port 2), stable radiation patterns and good diversity characteristics (the minimum isolation > 16 dB, the envelope correlation coefficient < 0.01, the channel capacity loss < 0.08 bps/Hz, and the total active reflection coefficient < -4.1 dB, etc.) in the whole impedance bandwidth. The research results can provide a useful reference for the design of UWB-MIMO ground antennas based on the theory of characteristic modes.

An aperture coupled printed antenna using frequency selective surface (FSS) reflector is reported in this paper. The proposed antenna includes two layers of FSS reflectors designed with an array of 7×5 crossed elements on the top substrate to achieve wideband, high gain and improved directivity. The antenna implements an aperture coupled radiating element on the bottom substrate which serves as a source feed antenna to the FSS reflector. The proposed structure has an overall dimension of 30×32×1.6 mm³ operating between 6.5 and 8.3 GHz with an impedance bandwidth of 1.8 GHz. The results reveal that the impedance bandwidths in excess of 82.3% and 44.5% have been achieved compared to the source feed antenna and antenna with single layer FSS, respectively. Further, the peak gain of 6.25 dB is also achieved in the operational frequency band with a two-layer FSS which is 29.4% and 15.8% more than the antenna without FSS and antenna with single FSS layer. Due to compact structure, wideband, high gain, and fabrication simplicity, the proposed antenna may be suitable for long distance communication systems.

Wideband designs of proximity fed regular shape microstrip antennas using bow-tie and H-shape ground plane profile are proposed in 1000 MHz frequency range. The modified ground plane alters the quality factor of the patch cavity which enhances the impedance bandwidth. In terms of the results obtained for bandwidth and gain together, circular and square patches backed by bow-tie shape ground plane, followed by circular patch backed by H-shape ground plane yield optimum results. For substrate thickness of 0.097λ_g, against the conventional ground plane, bow-tie shape gives 12% and 24% bandwidth increment for circular and square patches, respectively, and H-shape ground plane yields bandwidth increment by 17% in circular patch. All these wideband designs offer peak gain around 6 dBi with a broadside radiation pattern. Further, modified ground plane profile helps in optimizing the proximity fed antennas on lower substrate thicknesses. Amongst all the configurations, for ~0.03λ_g reduction in the substrate thickness, SMSA using bow-tie shape ground plane yields 19% increase in the impedance bandwidth against the equivalent thicker substrate design with a peak broadside gain of above 6 dBi. Thus, proposed modified ground plane antennas yields bandwidth improvement but for a smaller substrate thickness.

A flexible and reliable full-wave modal integral method is proposed to efficiently characterize planar transmission structures printed on multilayered isotropic/anisotropic substrates. Based on the mathematical concept of operators used in electromagnetism, it consists in determining the modal inner products obtained through the Galerkin's procedure via a proper choice of trial functions with metallic edge effects. To this aim, a fast and accurate nonuniform discretization algorithm is introduced for the first time, while using a new process to accelerate the convergence with regard to the number of areas of such inner products, thus significantly reducing the required CPU-time for planar transmission lines analysis. To demonstrate the efficiency of the proposed numerical integral approach, a successful comparison was achieved through a close agreement with published data.

Aiming at the shortcomings of complex broadband transmitter/receiver systems and inflexible bandwidth control in the existing inverse synthetic aperture radar (ISAR) imaging systems, in this paper, a novel two-dimensional imaging method based on frequency diverse ISAR (FDISAR) is proposed by combining frequency diversity technique with inverse synthetic aperture technique. In the imaging process, FDISAR is different from the stepped-frequency ISAR, which needs to transmit the same burst at different observation moments. Once the bandwidth is determined, the bandwidth of the subsequent burst synthesis cannot be changed, which reduces the flexibility of the radar system. In this method, single-frequency signals of different frequencies are transmitted to the target at different observation times, and the wideband signals are synthesized using the frequencies at different observation times to obtain the resolution capability in the range direction. In addition, the relative motion synthetic aperture of the target and radar is used to obtain the azimuth resolution capability, and finally the two-dimensional imaging capability of the moving target is formed. Specifically, we established an ISAR imaging model based on frequency diversity to synthesize a broadband signal, and used an improved backward projection algorithm (BP) to complete the two-dimensional imaging of the target. On this basis, the influence of the transmission signal frequency selection on the imaging quality is analyzed, and the half-power resolution in range and azimuth directions is derived. Furthermore, in order to eliminate side lobes and improve imaging quality, we combined compressive sensing (CS) theory with a BP imaging algorithm based on compressed sensing to obtain high-quality target 2D images. Simulation and actual measurement results show that FDISAR can achieve two-dimensional imaging of moving multi-scattering point targets. The application of this method is of great significance for reducing the complexity of the ISAR imaging system and improving the flexibility of the system's control bandwidth resources.

In this communication, a compact Dielectric Resonator (DR) based multiple-input-multiple-output (MIMO) antenna is presented for wideband applications. The antenna consists of two modified kite-shaped monopoles where four DRs have been placed on the patch. Corners of four DRs have been etched to implement the orthogonal phase, which leads to circular polarization characteristics. Implementation of DRs also helps in bandwidth enhancement purpose. Two L-shaped parasitic strips along with a Y-shaped stub have been used in the ground plane so as to obtain high isolation, which leads to a decrease of mutual coupling between the antenna elements. The proposed antenna achieves a wide impedance bandwidth of 7.1-22 GHz (106%) along with low mutual coupling of less than -15 dB within the entire frequency range as well as circular polarization characteristics, which covers the frequency range (-3 dB) of 7.1-7.9 GHz (10.6%). Thus the antenna can be considered as a potential candidate for modern wireless communication systems.

In this manuscript, the realization of penta-band notches with the aid of an ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna for diverse wireless applications is demonstrated. A single port UWB antenna is utilized to construct the proposed MIMO antenna, which comprises an altered patch loaded with three U-shape slots and an inverse U-shape slot on the feed line followed by a C-shape stub adjacent to the feed line. These slots and C-shape stub are liable to generate five notches at 3.4 GHz (3.16-3.67 GHz), 4 GHz (3.88-4.10 GHz), 4.6 GHz (4.56-4.75 GHz), 5.7 GHz (5.65-5.92 GHz), and 7.8 GHz (7.39-8.12 GHz), respectively. These notches depreciate interference from WiMAX, C-band, WLAN and X-band (satellite communication) frequencies. Alternatively, the reported antenna can also be utilized as a proximity radar (8-12 GHz) in X-band. The proposed antenna engraved on a Rogers RT/Duroid 5880 substrate having an overall size of 80 × 80 × 1.6 mm³ or 0.8λ₀ × 0.8λ₀ × 0.016λ₀ (λ₀ is the free-space wavelength at lowest frequency 3 GHz). Simulation and experimentation have been performed to corroborate the performance of the reported antenna. Results emphasize that the proposed MIMO antenna operates from 3 GHz to 14 GHz with measured peak gain 4.8 dBi, radiation efficiency above 82% and isolation less than -20 dB. Except at notches, the computed envelope correlation coefficient (ECC) is less than 0.03; diversity gain (DG) is approximately 10; total active reflection coefficient (TARC) is less than -10 dB; channel capacity loss (CCL) is less than 0.35 bps/Hz. These characteristics qualify it as a multifunctional antenna for wireless applications, lowering the antenna count needed in compact wireless devices.

In this paper, a single band two element MIMO antenna for future 5G wireless applications at 5 GHz is presented. The antenna consists of T over T shaped meander micro strip lines printed on the front side and defected ground structure on the back side of an RT Rogers 5880 substrate, which are able to excite a resonance mode. The antenna operates at 4900 to 5060 MHz (|S₁₁| < -10 dB) covering the 5G NR band n79. The antennas are to be placed symmetrically along the edges at the corners of the Smartphone panel. The isolation in the case of two elements MIMO antenna is enhanced by an I-shaped ground slot. The mutual coupling reduction is facilitated by 10 mm neutralization line (NL) at both hands. The prototype is fabricated to validate the proposed model. The measured results show good accordance with simulated results. The main performance results wherever possible of the proposed design are calculated, compared and analyzed with the measured results.

A transmissive single-layer Huygens unit cell based on induced magnetism is proposed to design low-profile and multi-focus metasurface. The Huygens unit cell consists of a pair of antisymmetric metal elements and a dielectric substrate with only 1.2 mm thickness (λ₀/6.8 at 37 GHz). The surface currents flowing in the opposite directions form the circulating electric currents to induce the magnetic currents orthogonal to the electric currents. The full coverage of 2π phase is achieved through optimizing the parameters of the metal elements, which solves the problem of the incomplete phase coverage caused by layer number reduction. With Holographic theory, the compensating phase distribution on the metasurface is calculated. The incident plane wave can be converged to designated points in any desired fashion including focal number, location and intensity distribution, which exhibits outstanding manipulation capability. As the simulations and measured results show, the designed metasurface can achieve good multi-focus focusing characteristics. The focusing efficiency at the center frequency is 43.78%, and the relative bandwidth with 20% focusing efficiency exceeds 20%. The designed metasurface has the advantages of low profile, simple processing, and high efficiency, which has a wide range of application prospects in the fields of millimeter wave imaging, biomedical diagnosis and detection.

We presented a miniaturized defected ground structure-based millimeter-wave (MMW) contemporary MIMO antenna for 5G smart applications devices. The proposed MIMO antenna offers many advantages including high gain, compactness, planar geometry, wide impedance bandwidth, and reduced mutual coupling effects performance. The top layer of the proposed four-port MIMO antenna design comprises 1x2 rectangular patch array structures, with each placed at the middle of a 20x20 mm² substrate of material (RO4350B) having thickness of 0.76 mm and loss tangent of 0.0037. For miniaturization and better performance, both the ground layer and radiating patches are defected with slots of a rectangular shape while an E-shaped slot is placed at the center of the ground plane. The operating impedance bandwidth of the proposed antenna ranges from 26.4 to 30.9 GHz incorporating the dominant portion of the mm-wave band. The proposed MIMO antenna is also characterized by the fundamental MIMO performance metrics such as Envelope Correlation Coefficient (ECC) which is less than 0.12 for any two-element array that encounters the mandatory standard of <0.5, high Diversity gain (DG) reaching its ideal value of 10 as well as minimum isolation of -19 dB with a total efficiency of 85% at 28 GHz. These characteristics make the proposed compact four-port MIMO antenna one of the best candidates to be used in 5G portable devices.