A modified ant lion optimization (MALO) algorithm is proposed in this article, for the synthesis of Chebyshev-based arrays by optimizing amplitudes and phases of excitations, and element spacings. Modification in ant lion optimization is achieved by hybridizing it with chaotic particle swarm optimization. The optimization process is employed to obtain an array pattern with the least possible sidelobe level. Close-in sidelobe level minimization for optimum pattern synthesis is suggested. Instead of only steering the main beam towards the desired direction presented by some popular optimization methods, the beam steering along with null positioning in other specified direction is also achieved employing MALO. Considering the arrays with the same design parameters and the results of other optimization algorithms, the performance of MALO is evaluated. The results show that MALO provides considerable improvements in an array pattern compared to the arrays optimized using other optimization algorithms and the uniform array.

The current paper describes the design of a fourth-order compact narrow-band hairpin-line bandpass filter centered at 2.5 GHz and enhanced stopband suppression ~38 dB required for wireless local area network (IEEE802.11b). The size reduction of 24% has been achieved for a conventional hairpin-line filter with a second-order inward folding of the open-end arms with an improvement in the skirt characteristics. However, the folding mechanism has been overshadowed by the presence of spurious harmonics with an attenuation level of <10 dB. Subsequently, L-shaped spurlines with optimum dimensions have been incorporated in the coupled arms of the folded hairpin-line cells. Three fourth-order filters have been designed with the incorporation of spurlines in different coupling regions, fabricated, and tested experimentally. Accordingly, an extended stopband with a rejection level of 38 dB up to 4.48f0 and a size reduction of 18% over the conventional hairpin-line filter has been achieved.

A suspended-stripline Gysel low-insertion-loss power combiner is presented in this paper. The multi-layer cavity structure reduces the circuit size and increases power density, composed of suspended strip lines and coaxial lines. The transmission-line theory is used to analyze this proposed power combiner, and the equivalent circuit model is developed to investigate the characteristics and design of the power combiner. The measured input return loss is greater than 20 dB from 7.15 to 9.35 GHz. The measured insertion loss is less than 0.36 dB, and the power-combining efficiency is greater than 92% from 7.39 to 9.19 GHz. The maximum power-combining efficiency is 98.8% at 8.1 GHz. Besides, the measured isolation is greater than 20 dB from 7 to 10 GHz. The power capacity is analyzed, and the cross-sectional power density is greater than 3.57 kW/cm2. The measured and simulated results show reasonable agreement with each other.

In this paper, the design of frequency reconfigurable planar antenna by incorporation of metasurface superstrate (FRPA-MSS) is presented using an artificial neural network. The dual-layer radiating structure is created on a 1.524 mm thick Rogers RO4350B substrate board (εr = 3.48, tan δ = 0.0037). The candidate antenna is designed and analyzed using a high-frequency structure simulator (HFSS) tool. The transfer matrix method is employed for the successful retrieval of electromagnetic properties of the metamaterial. Frequency reconfiguration is achieved by placing the metasurface superstrate onto the rectangular patch antenna. A simplified ANN approach has been employed for the design of metasurface incorporated proposed antenna. Presented prototypes are characterized through experimental measurements. It is found from the practical observations that the proposed antenna effectively reconfigures the tuning range from 5.03 to 6.13 GHz. Moreover, the presented antenna operates efficiently with agreeable gain, good impedance matching, and stable pattern characteristics across the entire operational bandwidth. The experimental results obtained validate the simulated performance.

In this paper, a novel multiband implantable planar inverted-F antenna (PIFA) antenna based on Gosper curve fractal geometry is designed for biomedical telemetry applications. The antenna has covered four dedicated frequency bands; medical implant communication system band (MICS 402–405 MHz), industrial, scientific, and medical bands (ISM 902–928 MHz and 2.4–2.5 GHz), and wireless medical telemetry services (WMTS 1395–1400 and 1429–1432 MHz). The proposed antenna is designed on Rogers RO 3010 substrate of thickness 25 mil and volume equal to 153.67 mm3. The reflection coefficient and the radiation pattern are measured inside muscle-mimicking liquid tissue phantom. The antenna has achieved the impedance bandwidth of 126, 406, 168, and 175 MHz at MICS (403 MHz), ISM (915 MHz), WMTS (1400 MHz), and ISM (2.45 GHz) with maximum gain value −33.6, −21.04, −15.48, and −10.25 dBi, respectively. The data link range between the implantable antenna and off body antenna has been performed with −16 dBm input power. Additionally, the obtained specific absorption rate with the input of 25 μW power has also been obtained within the safety limit and hence ensures the reliability of the proposed antenna.

Large truncated spherical near-field systems with conductive or absorbing floors are typically used in the measurement of the performances of vehicle-installed antennas. The main advantage of conductive floor systems is the ease of accommodation of the vehicle under test, but their performances are affected by the interaction with the reflecting ground floor. Instead, absorbing-based systems emulating free-space conditions minimize the effect of the interaction with the floor, but generally require longer setup times, especially at lower frequencies (70–400 MHz), where bulky absorbers are typically used to improve reflectivity levels. Considering scaled measurements of a vehicle model, the performances of these two typical implementations are analyzed in the 84–1500 MHz range and compared to free-space measurements. Absorbers with different dimensions and reflectivity have been installed in the scaled measurement setup, and measured data have been investigated with proper post-processing to verify the applicability to realistic systems. Figures of merit of interest for automotive applications, like gain and partial radiated powers, have been compared to free-space to evaluate the impact of different scenarios.

This paper presents the design of a sixth-order cross-coupled L-band filter, specifically intended for space applications. The solution was based on the principle of stepped impedance coaxial resonators (SIRs), which allowed us to fulfill several electrical and size specifications and more particularly a high multipactor threshold. The degrees of freedom afforded by the proposed topology offer a wide choice of design configuration possibilities. Whatever the central frequency and required specifications, several compromises can be made in terms of volume, height, footprint, quality factor, multipactor threshold, harmonic rejection, etc. For instance, SIR coaxial topology is very well suited to small L-band filters when moderate quality factors and multipactor thresholds of around 4000 and 400 W, respectively, are requested. The design procedure is presented and simulations and measurements are compared and discussed.

Sensors based on metamaterial absorbers are very promising when it comes to high sensitivity and quality factor, cost, and ease of fabrication. The absorbers could be used to sense physical parameters such as temperature, pressure, density as well as they could be used for determining electromagnetic properties of materials and their characterization. In this work, an attempt has been made to explore the various possible applications of these sensors. Metamaterial-based sensors are very popular for its diverse applications in areas such as biomedical, chemical industry, food quality testing, agriculture. Split-ring resonators with various shapes and topologies are the most frequently used structures where the sensing principle is based on electromagnetic interaction of the material under test with the resonator. Overcoming the design challenges using metamaterial sensors involving several constraints such as cost, compactness, reusability, ease in fabrication, and robustness is also addressed.

By combining multiple input multiple output (MIMO) technology and multiple matched filters with frequency diverse array (FDA), FDA-MIMO radar can be used to achieve two-dimensional target localization with range and angle. In this paper, we propose two FDA-MIMO multi-pulse target localization methods based on tensor decomposition. Based on the canonical polyadic decomposition theory, the signal models of CPD-DP-FDA with double-pulse and CPD-SP-FDA with stepped frequency pulses are established. By analyzing the signal processing procedures of the two schemes, the indicator beampattern used for target localization is obtained. The parameter estimation accuracy of the proposed method is investigated in single target and multiple targets scenarios, and the proposed method is compared with the traditional double-pulse method. The results show that the target localization method based on tensor decomposition can effectively solve the problem of multi-target indication ambiguity. The target positioning effect can be further improved by combining stepped frequency pulses. The derivation of Cramer–Rao Lower Bound (CRLB) demonstrates the superiority of the method.

In this paper, we propose a frequency-reconfigurable antenna structure consisting of a dielectric resonator (DR) topped by a superstrate material. Two metasurfaces (MSs) are placed upon the DR and the superstrate, where these two MSs are utilized to synthesize a localized reduction of the dielectric constant of the DR. By placing switches into one of the MSs, the distribution of dielectric constant of the DR can be switched to one of two predefined distributions, which is equivalent to switching the DR length to two different lengths. Consequently, the frequency response of the proposed structure can be tuned to one of two operating bands. The excited modes inside the proposed antenna were obtained analytically and through simulations. Also, the dielectric constant value of substrates topped by MSs was analyzed. The antenna was fabricated and measured, and good agreement between simulation and measurement was attained. The antenna bandwidths are 7–8.1 GHz (14.7%) and 8.5–9.2 GHz (8%) and the gains are 5.1 and 7.8 dB, in the cases of having switches off and on, respectively.

The launch of the Sentinel-1B satellite in April 2016 completed the two-satellite synthetic aperture radar (SAR) constellation of the European Copernicus Sentinel-1 mission. The European Space Agency executed the calibration of this sensor during the commissioning phase and an independent calibration by the German Aerospace Center (DLR) in 2016. The calibration parameters must be monitored to assess the stability of the instrument. This study reports the temporal stability assessment of radiometric calibration and image quality parameters of Sentinel-1B SAR data using the corner reflector (CR) array, Surat Basin, Australia. Impulse response functions generated from the CRs in the satellite images were used to derive the image quality parameters. The average radar cross-section difference between estimated and theoretical values (38.40 dB m2) was 0.53 dB m2 for 1.5 m CRs, which is accordant with the absolute radiometric accuracy specified for the Sentinel-1 SAR system. Derived image quality parameters viz. the mean peak-to-side lobe ratio, mean integrated side lobe ratio, and spatial resolutions in the range and azimuth directions were found to be accordant with the specified value for the Sentinel-1 SAR system. The results indicate the excellent quality of the Sentinel-1B data.

This paper presents a systematic comparison of the relationship between transmission line characteristic impedance and Q-factor of CPW, slow-wave CPW, microstrip, and slow-wave microstrip in the same CMOS back-end-of-line process. It is found that the characteristic impedance for optimal Q-factor depends on the ground-to-ground spacing of the slow-wave transmission line. Although the media are shown to be similar from a mode of propagation point of view, the 60-GHz optimal Q-factor for slow-wave transmission lines is achieved when the characteristic impedance is ≈23 Ω for slow-wave CPWs and ≈43 Ω for slow-wave microstrip lines, with Q-factor increasing for wider ground plane gaps. Moreover, it is shown that slow-wave CPW is found to have a 12% higher optimal Q-factor than slow-wave microstrip for a similar chip area. The data presented here may be used in selecting Z0 values for S-MS and S-CPW passives in CMOS that maximize transmission line Q-factors.

In this paper, a dual-band 8 × 8 multi-input multi-output (MIMO) array antenna operating in 3.5 GHz band (3400–3600 MHz) and 5.5 GHz band (5150–5925 MHz) for 5G mobile handset is presented. The proposed hybrid antenna includes a comb-shaped monopole and an L-shaped open slot antenna which are symmetrically located on the inner surface of the side-edge frame of smartphone. Pattern diversity is achieved that can mitigate envelope correlation coefficients (ECCs) and improve the MIMO system performances. The prototype of proposed dual-band eight-element MIMO antenna is fabricated and experimentally measured. The results show that isolation <−10 and <−15 dB, respectively in the lower band and high band without any additional decoupling element are achieved and the desired bands are satisfied under the condition of −6 dB impedance matching. Moreover, the essential parameters for evaluation of the MIMO system performance such as the ECC, mean effective gain (MEG), and ergodic channel capacity are calculated. Furthermore, the influence of user's hand on the radiation characteristics of proposed MIMO antenna are also investigated and discussed. Based on the result, the proposed MIMO antenna is a good candidate for use in future 5G applications.

Full duplex (FD) could potentially double wireless communications capacity by allowing simultaneous transmission and reception on the same frequency channel. A single antenna architecture is proposed here based on a modified rat-race coupler to couple the transmit and receive paths to the antenna while providing a degree of isolation. To allow the self-interference cancellation (SiC) to be maximized, the rat-race coupler was made tuneable. This compensated for both the limited isolation of the rat race and self-interference caused by antenna mismatch. Tuneable operation was achieved by removing the fourth port of the rat race and inserting a variable attenuator and variable phase shifter into the loop. In simulation with a 50 Ω load on the antenna port, better than −65 dB narrowband SiC was achieved over the whole 2.45 GHz industrial, scientific and medical (ISM) band. Inserting the S-parameters of a commercially available sleeve dipole antenna into the simulation, better than −57 dB narrowband SiC could be tuned over the whole band. Practically, better than −58 dB narrowband tuneable SiC was achieved with a practical antenna. When excited with a 20 MHz Wi-Fi signal, −42 dB average SiC could be achieved with the antenna.

The design and first experimental results of Tx and Rx L-band bandpass filters for a high-power satellite diplexer are presented in this paper. Designed in the framework of an ESA ARTES AT project, the filters are based on TM010 mode dielectric resonators. These resonators allow for better results in terms of volume occupation with respect to other dielectric resonators still maintaining high Q-factor values (>2000). Volume saving above 30% is achieved with respect to standard coaxial filters. The filter geometries and materials have been chosen in order to improve the power-handling and to cope with related critical issues for space applications (i.e. avoid any multipactor discharge in the operating RF power range and low-PIM response). Measurements of Tx filter show good correlation with the design in terms of central frequency, BW, and unloaded Q-factor (almost 3000). Measurements of Rx filter show a worse correlation with the design in terms of filter response shape. This is ascribed to size tolerances of one of the filter resonators. Multiple analyses are ongoing to remove this degradation in the final engineering model.

The factorization method (FM) is an attractive qualitative inverse scattering technique for the detection of geometrical features of unknown objects. This method depends on the selection of regularization parameters slightingly and has low calculation necessities. The aim of this work is to present a near-field FM for inverse source problems that have many applications. A modified test equation is obtained by converting the far-field term to Hankel's function. A different method has been proposed by manipulating the asymptotic approximation of Hankel's function in order to obtain near-field equations with incident angle and distance parameters. The novelty of this study is an integral equation based on the FM, which consists of multifrequency sparse near-field electric field measurements. We proved that the solution of the proposed integral equation gives information about the location of scatterers. The proposed algorithm is validated with simulation results and the capabilities of the presented method are assessed with several frequency regions and sources. Additionally, the presented method is compared with the direct sampling method in order to understand the performance of the proposed approach over a given scenario. The developed FM provides accurate results for electromagnetic source problems.

This paper presents a novel compact dual-band printed antenna with an omnidirectional radiation pattern for 5G WLAN. The antenna element comprises a star-shaped patch with six disc-shaped elements at the top and a defected ground structure at the bottom, having a radius of 3.77 mm for both. The proper feeding point and alignment with its element parameters help to achieve good impedance matching. The proposed antenna has a single center feed, a low profile, and a straightforward compact structure without any feeding complexity. A high reception fidelity antenna with comparable bandwidth and moderate gain is presented. The prototype radiator was printed on a 4 mm radius and a 1.6 mm thick dielectric substrate (Rogers RT/Duroid 5880), with a dielectric constant of 2.2. The designed antenna is fabricated and measured to validate the simulation result. The measured impedance bandwidth of 1.3 GHz (27.5–28.8 GHz) and 2.2 GHz (32.45–34.65 GHz) with a respective measured gain of 1.1 and 3.2 dBi are achieved at 28 and 34 GHz. The simulated radiation efficiency of above 95% is achieved for both bands. A good agreement between simulated and measured results of the proposed work shows that the proposed antenna is suitable for 5G short-range WLAN communications.

This study illustrates the dynamical reconfiguration of a concentric hexagonal antenna array radiation to generate a pencil beam and flat-top beam simultaneously by electronic control in two principle vertical planes under consideration. Both the beams share a common normalized optimal current excitation amplitude distribution while the optimal sets of phase excitation coefficients are varied radically across the hexagons to generate a flat-top beam. The proposed approach is able to solve the underlying multi-objective problem and flexible enough to the efficient implementation of additional design constraints in the considered φ-planes. In this paper, a set of simulation-based examples are presented in an integrated way. The outcomes validate the effectiveness of the stated optimization using meta-heuristic optimization algorithms (teaching–learning-based optimization, symbiotic organism search, multi-verse optimization) to reach the solution globally and prove actual relevance to the concerned applications.

In this paper, an eight-shaped polarization-dependent electromagnetic bandgap (ES-PDEBG) structure is proposed. The unit cell of ES-PDEBG structure consists of an outer eight-shaped EBG patch with two inner square patches and three vias. Surface wave bandgap and reflection phase characteristics have been studied for the proposed structure. From the measurement results, two surface wave bandgaps with center frequencies 3.42 and 5.88 GHz are observed along the X-direction, and one surface wave bandgap with center frequency 3.69 GHz is observed along the Y-direction. The refection phase bandgap of the proposed structure is centered at 5.61 and 3.31 GHz for x- and y-polarized incident plane waves, respectively. Furthermore, the application of the proposed structure as polarization reflector is presented. The study demonstrates that the structure can act as dual-band in-polarization reflector for circularly polarized waves. In addition, incident linearly polarized waves are reflected as circularly polarized waves in four operating bands.

Wireless connectivity has been realized for multiple environments and different frequency bands. However, little research exists about mmWave communication in industrial environments. This paper presents the 60 GHz double-directional radio channel for mmWave communication in a ship hull for Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) conditions. We performed channel measurements using the Terragraph channel sounder at different locations in the ship hull and fitted LOS path loss to a one-slope path loss model. Path loss and root-mean-square delay spread of the LOS path is compared to the reflected path with lowest path loss. NLOS communication via this first-order reflected path is modeled by calculating the path distance and determining the reflection loss. The reflection losses have a considerable contribution to the signal attenuation of the reflected path. The channel models are implemented in an indoor coverage prediction tool, which was extended with a ray launching algorithm and validated by comparison with an analytical electromagnetic solver. The results show that the mmWave radio channel allows high-throughput communication within a ship hull compartment, even when no LOS path between the transmitter and receiver is present.