This letter, an ultra-wideband compact printed log periodic dipole (LPD) array antenna is designed to operate between 500 MHz and 6 GHz frequencies. The proposed LPD antenna structure consists of one bow-tie dipole and 15 regular dipole elements. The bow-tie element is introduced to improve the antenna's performance at the lowest frequencies below 1 GHz and at the same time to reduce the antenna size maintaining a good performance. An experimental antenna prototype has been designed, optimized, fabricated, numerically and experimentally assessed. The obtained results are very promising, and they demonstrated that the presented antenna prototype is able to operate in the range between 500 MHz and 6 GHz with an average gain of 6 dBi and a very compact size.

While analyzing wideband electromagnetic scattering problems using ultra-wideband characteristic basis function method (UCBFM), the reconstruction of a reduced matrix and the recalculation of an impedance matrix at each frequency point cost a large amount of time. To overcome this issue, a novel method that combines UCBFM with compressive sensing (CS) is proposed in this paper to rapidly analyse the wideband RCS. The proposed method makes the ultra-wide band characteristic basis functions (UCBFs) generated at the highest frequency as the sparse basis, introduces the CS theory, randomly extracts several rows from the original matrix as the measurement matrix, utilizes the corresponding excitation vector as the measurement value, and then employs the recovery algorithm, through which the solution of target induced current can be obtained. Due to partial filling of impedance matrix and efficient recovery algorithm, the wideband RCS computation time of the object is significantly reduced using the proposed method. Furthermore, the numerical simulation results show that the computation efficiency for the target wideband RCS can be further enhanced compared with that of the stand-alone UCBFM.

This paper presents a design of a right hand circularly polarized x-band reflectarray antenna (RA) at a center frequency 12 GHz. The reflectarray is fed by a linearly polarized dipole antenna. The proposed reflectarray antenna can be used for CubeSat applications. The reflecting elements have the shape of a pentagon. This shape is chosen to convert the incident linearly polarized fields to the required circular polarization. A dipole antenna is used as linearly polarized (LP) feeding element for the proposed reflectarray. This dipole antenna is tilted w.r.t the x-axis by an angle 45˚ to introduce nearly equal polarizations in x and y directions on the aperture of the reflectarray. Each reflecting element is adjusted to produce a phase shift 90˚ between the reflection coefficients in x and y directions. The required reflected phase is realized by adjusting a scaling factor (SF) for the pentagonal patch in x direction to the corresponding SF in y axis. This phase difference is responsible for polarization conversion of the incident plane wave into circularly polarized reflected wave. The reflectarray is designed with focal to-diameter (F/D) ratio equals unity. In this work, an efficient technique is discussed for modelling the reflectarray designed. This technique is based on developing a Visual Basic Script file for allocating the reflecting elements with their corresponding dimensions in their location on the simulation tool. This script file is used directly by the simulation tool (HFSS) to draw the complete model automatically. This procedure has a significant role on simplifying the modeling of complicated structure like the proposed reflectarray. The proposed reflectarray antenna is simulated at 12 GHz. The obtained axial ratio (AR) is found to be 2.1 dB, and peak gain is 18 dBi. The antenna is also fabricated and measured for verification.

In this article, a miniaturized pentagonal slot antenna (PSA) with a Meander Koch Defected Ground Structures (MK-DGS) and metamaterials (MTM) is proposed for 5 GHz WLAN application. Initially, a Meander Koch DGS was used to lower the resonant frequency of the basic PSA, from 13.1 GHz to 5 GHz. The proposed antenna has been 61.83% miniaturized, close to an electrically small antenna. The performance characteristics of a basic PSA using MK-DGS and MTM superstrate, which improves efficiency, directivity, and peak gain, are also discussed. An antenna with dimensions of 15 × 15 mm² (or) 0.25λ₀ × 0.25λ₀ mm² at a thickness of h1 = 1.6 mm is designed, fabricated, and tested on an FR4 epoxy substrate, and its impact on size reduction performance is evaluated. The gain at 5 GHz is increased from 3.15 to 7.84 dBi by introducing an MTM superstrate made of RT Duriod at a thickness of 1.575 mm above the miniaturized PSA at 17 mm. Test results of the prototype model are corroborated by the simulated results of the proposed model.

In this paper, a quad-band notch characteristics ultra-wideband (UWB) antenna for Wi-MAX, L-WLAN, U-WLAN, and C-band applications is presented. The initial UWB antenna bandwidth is achieved in the 2 to 12.5 GHz frequency band by using the partial ground method. Spiral lossy resonator (SLR) slots are loaded into the UWB ground structure to achieve quad-band notch characteristics. Each SLRS circuit is accountable for a single notch characteristic by losing EM power at the notch frequency. A quad-band notch is accomplished in this antenna for WiMAX (3.24 to 3.56 GHz), L-WLAN (4.76 to 5.34 GHz), U-WLAN (5.58 to 5.91 GHz), and C-band (7.37 to 7.71 GHz) by loading four SLR slots circuits into the UWB antenna. The proposed antenna is engraved on a Rogers RO4003C (3.55) substrate having an overall volume of 50*40*1.524 mm³. The proposed antenna's performance has been verified through simulation and experiments.

In this paper, an ultra-wide band modified slot-sinuous antenna has been designed to enhance bistatic radar cross section (RCS) response. The design procedure consists of adding three or five parasitic ellipses openings to each of the slot-sinuous arm cells. The parasitic ellipsis allows to control bistatic RCS without impacting antenna radiation characteristics. Parasitic ellipses opening dimensions are small compared to the relative wavelength of the signal on each active region of the antenna. Ellipses deploy over the entire sinuous arms are scaled by the same expansion coefficient used to design the antenna itself. In the proposed design, ellipses parameters such as ellipses axis, radial position, and relative angle position on the sinuous cell are key parameters to be optimized for bistatic RCS reduction. The total number of designing parameters is finite, but their combination is infinite, which leads to the possibility of designing different antennas based on the required designing goals. The proposed solution and the results presented in this work show the applicability of the designing parameters to control bistatic RCS on active region antennas.

Traditional genetic algorithm identification of permanent magnet synchronous wind generator (PMSWG) parameters is easy to fall into local optimum, resulting in low accuracy of parameter identification results and slow convergence, which reduces the accuracy of parameter tuning of proportional-integral (PI) controller. Aiming at this problem, a chaotic mapping simulated annealing genetic algorithm (CMSAGA) for identifying PMSWG parameters is proposed. The traditional genetic algorithm (GA) has the ability of global random search, combined with the probability breakthrough characteristic of the simulated annealing (SA) algorithm, which avoids the parameter identification result falling into the local optimum and finally tends to the global optimum. With the increase of iteration times, the initial population is mapped with tent chaos mapping theory, and the optimal value of the population is disturbed in each iteration to increase the diversity of the population, making the proposed algorithm converge faster and improve the accuracy. Experiments show that the proposed algorithm has good accuracy and convergence speed, PMSWG stator resistance, stator winding d-q axis inductance and permanent magnet flux can be identified.

The design of a Complementary Split Ring Resonator (CSRR) embedded compact Asymmetric Coplanar Strip (ACS) fed monopole antenna is presented in this paper. By incorporating the ACS feed, a substantial reduction of 27% in antenna dimensions is achieved. Further miniaturization of 68.6% is obtained by embedding CSRR on the designed patch and a trapezoidal ground. The overall size of the antenna is 13.2 × 27 × 1.6 mm³, and it is printed on an FR4-epoxy substrate. The antenna operates with a resonant frequency of 3.6 GHz and a bandwidth of 3.3 GHz (3.2-6.5 GHz). Thus it is appropriate for sub-6 GHz 5G applications. It exhibits a return loss of -28 dB and a gain of 2.8 dBi at the resonant frequency. The antenna is fabricated, and the measured results match well with the simulated ones. Being a simple, cheap, and uniplanar structure, the proposed antenna can meet the requirements of a modern wireless communication system.

Radio Frequency Identification (RFID) technology is one of the simplest forms of wireless communication systems. It is a unique concept that aims to connect and identify tagged assets or objects to RFID readers to collect information. This paper presents the design and implementation of a compact dual-band RFID applications. The proposed design is a microstrip anetnna composed of two coupled armed meander-lines having 90° between them to achieve circular polarization. The proposed design is mounted on a 1.6 mm thick FR4-epoxy substrate backed by a partial ground plane with the total area of (58 x 80 mm²) to ensure compact size of the tag. The designed antenna is fed through a 50-ohm transmission line of length 28.5 mm. The antenna is considered dual bands that resonate at 850 MHz and 1.5 GHz and radiates circularly polarized waves with axial ratio about 1.4. The simulation results using HFSS software showed promising performance with a bandwidth of 141 MHz at center frequency 850 MHz and 287 MHz at centre frequency 1.5 GHz, respectively after optimizing the proposed design of the tag antenna. The S₁₁ parameter shows return loss at -21 dB at 850 MHz band while at the higher frequency the return loss is much better which was -39 dB. The design provides a perfectly omnidirectional radiation pattern and high radiation efficiency of 93%. Fabrication of the proposed design is done with practical results having a similar trend to the simulated ones to convey good performance of the designed antenna.

A novel wideband cross-polarized coding metasurface has been presented in this paper towards reduction of monostatic radar cross section (RCS). A broadband reflective cross-polarization converter for linearly polarized (LP) electromagnetic waves covering both X and Ku bands has been designed for this purpose. The proposed unit cell is ultrathin (λ/15.7) and demonstrates a polarization conversion bandwidth of 10.84 GHz from 7.96 GHz to 18.8 GHz for a linearly polarized normal incidence wave which helps in reduction of radar cross section. In order to have a better understanding of cross polarization conversion (CPC), the physical mechanism of the structure has been investigated and elucidated in detail, along with the surface current distribution. The proposed structure has been studied for both transverse electric (TE) and transverse magnetic (TM) polarizations. For 1 bit coding, the suggested unit cell is utilized as the `0' bit, while the 90˚ rotated version of the unit cell is used as the `1' bit. A 4 × 4 matrix is built, and 16 configurations are explored. These combinations are known as the 2 × 2 metasurface sub-blocks, and they are used to build 200 × 200 components with size of 180 mm × 180 mm. The RCS simulation studies have been carried out from 2 to 30 GHz, and the proposed design shows a 10 dB RCS reduction from 10 GHz to 20 GHz. The scattering pattern of the suggested metasurface is comprehensively analyzed at 10 GHz, 15 GHz, and 18 GHz and demonstrates diffuse scattering in the other direction, minimizing the forward scattering RCS. The designed structure of 2.4 mm thickness has been fabricated and measured in the X and Ku bands. The measured results are in good agreement with simulated ones. In order to show the efficiency of the proposed coding metasurface, monostatic RCS estimation of the wing and body sections of high altitude aerospace paltforms (HAPS) has been simulated, and a 14.32 dB reduction has been observed over the body cross section.

In this paper, a low-profile dual circularly polarized (CP) antenna for Ku band satellite communication is proposed. A quarter-mode SIW (QMSIW) is designed as a circular polarization unit, which realizes circular polarization by using high-order mode TE₁₃₀, and a pair of units are combined to form the antenna proposed in this paper. Feeding different units can realize left-handed circular polarization and right-handed circular polarization, respectively. The antenna impedance bandwidth is 5.66 GHz (15.16 GHz-20.82 GHz); the circular polarization bandwidth (CPBW) is 540 MHz (15.64 GHz-16.18 GHz); and the gain in the passband is 5.1 dBi, with a minimum axial ratio (AR) of 1 dB. The thickness of the antenna is only 1.5 mm, which has obvious low-profile characteristics.

This paper presents a 3D printed extended hemispherical lens antenna for Body Centric Communications in 60 GHz band. The prototype consists of a 3D printed lens made of Polylactic Acid with three planar broadside patch antenna elements used as a source for the lens. The direction of the main beam antenna is switched by changing the excitation of source elements. The measured overlapping impedance bandwidth of the fabricated antenna is from 57.27 GHz to 60 GHz with reflection coefficient better than -10 dB. The main beam direction switches in broadside direction with 3 dB angular coverage from -29.2° to +30° by changing the radiating elements at 60 GHz. The measured gain is 15.28 dBi at 60 GHz. The beam switching capabilities and high gain with broadside radiation characteristics make the proposed antenna a suitable candidate for off-body links at 60 GHz. The effect of placing the antenna structure over the body is also studied in this paper. The body to off-body link measurement is successfully demonstrated with extended lens over the body and an open-ended waveguide as an external node.

The paper proposes the design of an ultra-wideband MIMO antenna with low mutual coupling and dual-band elimination characteristics. The proposed structure consists of a microstrip-fed monopole antenna with a stub to enhance the isolation for ultra-wideband applications. The dual rejection bands corresponding to WiMAX and WLAN frequencies are designed using electromagnetic band-gap structures of mushroom-type and placed close to the microstrip transmission line of the designed antenna. The isolation enhancement of |S₂₁| > 20 dB is achieved over the impedance bandwidth by adding two counter-facing F-pattern stubs to the ground. The impedance bandwidth of 9 GHz (2.65-11.65 GHz) for VSWR < 2.13 with the notch bands of 3.6-4.2 GHz and 5.15-5.87 GHz is obtained. The diversity gain, correlation coefficient, radiation pattern, TARC, and peak gain are also studied in the paper. The simulated and measured results are in close agreement with each other. Therefore, the proposed structure is a potential candidate for wireless communication.

In this paper, a bandwidth improvement technique in substrate integrated waveguide (SIW) slotted antennas is presented. Here, wideband is achieved by using a single cavity mode (TE₂₁₀) instead of multiple cavity modes, which is the most distinct approach as compared to other SIW based antennas. When the rectangle slot is loaded at bottom surface of the cavity, the TE₂₁₀ cavity mode of the antenna is perturbed. As a result, two independent modes namely odd TE₂₁₀ and even TE₂₁₀ are successfully generated and merged in close proximity. Consequently, an impedance bandwidth of 12.8% is obtained. When a vertical slit is added at each end of the rectangle slot to make as an I-shaped slot, the impedance bandwidth is increased from 12.8% to 13.94%. The fabricated antenna shows the measured impedance bandwidth of 14.4% andexhibits a gain of 5 dBi to 7 dBi throughout the operating band. The proposed design still retains many features such as light weight, easy fabrication, and easy integration.

In this communication, a new compact UWB dual port multiple-input multiple-output (MIMO) antenna is presented for wireless application. The design utilizes the property of dielectric resonator to achieve a bandwidth that ranges from 3.1 GHz to 18.5 GHz. The design has a compact size of 19×30×0.8 mm³. It consists of two rectangular shape monopole antenna elements with rectangular dielectric resonators sharing a similar ground plane. On the ground plane, a modified Hilbert curve with a meander line parasitic element was introduced to improve isolation between radiating elements which reduces mutual coupling issues. A band notch is achieved at WLAN band (5.09-5.8 GHz) by etching a pair of L-shape slots on each radiator. The gain of the antenna drops significantly at the centre of the notch band which indicates good interference suppression. Results show that the designed antenna provides a wide impedance bandwidth (below -10 dB) throughout the operating band of 3.1-18.5 GHz (142.6%). The antenna also produces nearly -20 dB isolation for the entire operating band. Results show that the simulated characteristics are in good agreement with the measured counterpart.

In recent times, the study of flexible wireless devices has attracted ample attention in the fields of biomedicine and healthcare. Biomedical systems are becoming more popular and employed to find harmful elements within human bodies. A portable biomedical device makes use of a contacting or non-contacting way to find tumours inside the human body. In view of this, a compact two-slot hexagonal shape flexible wideband microstrip antenna for healthcare application is presented. The proposed antenna is designed using a low-cost, light-weight, and broadly accessible flexible foam material. The slots incorporated into the geometry have enriched the percentage bandwidth of 106.67% with a total gain of 4.67 dBi. The flexible wideband antenna of dimension 28×26×2 mm³ is fabricated using copper foil. The designed and fabricated antenna operates over the frequency of 2.94 to 9.66 GHz resulting in three different resonating frequencies; 3.8 GHz, 6.7 GHz, and 9.1 GHz. The flexible antenna is tested under different bending conditions and obtains good performance to substantiate flexibility. The Specific Absorption Rate (SAR) analysis is also performed over a three-layer tissue equivalent body model and observes a maximum SAR value of 1.9 W/Kg less than the safety limit of 2 W/Kg for 10 gm of tissue. A good agreement is observed between the simulated and measured results of the proposed antenna for free space and human proximity.

In this study, a double reentrant cavity sensor (DRECS) loaded with ring gaps is proposed to characterize the displacement that the metal plate is inserted into the DRECS. The conventional substrate-parasitic-capacitance of DRECS in the substrate integrated waveguide (SIW) configuration, which has no contribution to the sensitivity, is successfully eliminated by using a symmetric double reentrant cavity. The ring gaps are introduced in SIW DRECS to effectively suppress the fringe electric field around the post, and enlarge the range of displacement measurements. Additionally, a displacement model, which is characterized by the quantitative relationship between the resonant frequency of DRECS and insertion depth inside DRECS, is theoretically established with the help of the electric field distribution and the equivalent circuit of the DRECS. A prototype of the designed sensor is fabricated and measured. The sensor work at 1.5-3.1 GHz and the measured results are in good agreement with the simulated ones from the displacement model. The measurement results indicate that the sensor has a displacement test range of 27 mm and Q-factor of over 150, and can achieve high sensitivity of 58 MHz/mm.

Group delay distortions are critical for high quality transmissions in today's communication system. In this paper, we have proposed design and analysis of defected microstrip line-based Negative Group Delay Circuits (NGDCs) to compensate for group delay distortions. Initially, a tunable pulse shaped defection based NGD structure is designed wherein a variable resistor connection allows group delay tunability. The proposed design is able to generate a group delay (GD) tuning from 0 to -4.8 ns at 2.7 GHz as the resistance is varied from 1 kΩ to 1 MΩ. Further, we embedded two stubs to implement the switchable multi-band feature on the proposed NGDC design. The NGDCs are fabricated, and the measured results confirm the proposed concept. Lastly, we designed a tunable compact NGDC with inverted-U stubs inscribed inside a microstrip line. It generated GD tunability at different frequency bands with the aid of a variable resistor and switched the frequencies as required.

A miniaturized lumped-element quadrature hybrid with a high density stacked structure is proposed in a 24-layer low temperature co-fired ceramic (LTCC) substrate. Stacking vertical-interdigital-capacitors (VICs) and vertically-spiral-inductors are for an entire size reduction. The transition between inductors realized in the inner space of the inductor further improves the utilization of three-dimensional space. The overall size of the quadrature hybrid is only 10.1×3.8×2.4 mm, or equivalently 0.0040×0.0015×0.0009λ_g³, which achieves a size reduction of 30.2%. Meanwhile, the proposed hybrid operates at 60 MHz with a fractional bandwidth (FBW) of 33.3%. The measured S₁₁, S₂₁, S₃₁ and S₄₁ are -14.5, -3.8, -3.7, and -14.2 dB within the operating frequency band, respectively, and both of the low phase imbalance and amplitude imbalance are achieved.

The article describes the problem of spatial separation of devices operating in the same frequency range. The possibility of focusing electromagnetic fields in several specified regions of space is considered. The proposed method for focusing the electromagnetic field can be an additional method for separation devices that operate in the same frequency range. The system under consideration, consisting of space, radiating antennas and focusing points, is represented as an abstract multipole with the number of inputs equal to the number of radiating antennas and with a set of outputs equal to the number of focusing points. A coordinate system has been introduced that makes it possible to calculate the distances between radiation and focusing points. A method for calculating complex transmission coefficients between emission points and reception points is described. An analytical expression is obtained, a system of linear algebraic equations, which makes it possible to calculate the necessary amplitudes and phases of signals supplied to radiating antennas. A model in a computer-aided design system containing 56 radiating antennas is presented. 9 focus points were set, and 4 of them should have maxima of the electromagnetic field. The simulation confirmed the theoretical calculations. A method for optimizing the calculations of the initial amplitudes and phases by eliminating the elements of the characteristic matrix is considered. This made it possible to reduce the number of elements in the characteristic matrix.