Showing papers in "International Journal of Antennas and Propagation in 2016"

Dielectric Resonator Antennas: Basic Concepts, Design Guidelines, and Recent Developments at Millimeter-Wave Frequencies

Abstract: An up-to-date literature overview on relevant approaches for controlling circuital characteristics and radiation properties of dielectric resonator antennas (DRAs) is presented The main advantages of DRAs are discussed in detail, while reviewing the most effective techniques for antenna feeding as well as for size reduction Furthermore, advanced design solutions for enhancing the realized gain of individual DRAs are investigated In this way, guidance is provided to radio frequency (RF) front-end designers in the selection of different antenna topologies useful to achieve the required antenna performance in terms of frequency response, gain, and polarization Particular attention is put in the analysis of the progress which is being made in the application of DRA technology at millimeter-wave frequencies

Optimal Pattern Synthesis of Linear Antenna Array Using Grey Wolf Optimization Algorithm

Abstract: The aim of this paper is to introduce the grey wolf optimization (GWO) algorithm to the electromagnetics and antenna community. GWO is a new nature-inspired metaheuristic algorithm inspired by the social hierarchy and hunting behavior of grey wolves. It has potential to exhibit high performance in solving not only unconstrained but also constrained optimization problems. In this work, GWO has been applied to linear antenna arrays for optimal pattern synthesis in the following ways: by optimizing the antenna positions while assuming uniform excitation and by optimizing the antenna current amplitudes while assuming spacing and phase as that of uniform array. GWO is used to achieve an array pattern with minimum side lobe level (SLL) along with null placement in the specified directions. GWO is also applied for the minimization of the first side lobe nearest to the main beam (near side lobe). Various examples are presented that illustrate the application of GWO for linear array optimization and, subsequently, the results are validated by benchmarking with results obtained using other state-of-the-art nature-inspired evolutionary algorithms. The results suggest that optimization of linear antenna arrays using GWO provides considerable enhancements compared to the uniform array and the synthesis obtained from other optimization techniques.

Array Mutual Coupling Reduction Using L-Loading E-Shaped Electromagnetic Band Gap Structures

Abstract: A mutual coupling reduction method between microstrip antenna array elements is proposed by using periodic L-loading E-shaped electromagnetic band gap structures. Two identical microstrip patch antennas at 2.55 GHz are settled together and used to analyze the performance of the designed two-element antenna array. The two antenna elements are settled with a distance of about . To reduce the mutual coupling, the L-loading E-shaped electromagnetic band gap structures are used between these antenna elements. The simulated and measured results show that the isolation of the antenna array reaches 38 dB, which has a mutual coupling reduction of 26 dB in comparison with the antenna array without the decoupling structures.

A Review of Computational Electromagnetic Methods for Graphene Modeling

Abstract: Graphene is a very promising optoelectronic material and has gained more and more attention. To analyze its electromagnetic properties, several numerical methods have been developed for graphene simulation. In this paper, a review of application of graphene in electronic and photonic device is provided, as well as some widely used computational electromagnetic algorithms for graphene modeling. The advantages and drawbacks of each method are discussed and numerical examples of these methods are given to illustrate their performance and application.

Evolutionary Algorithms Applied to Antennas and Propagation: A Review of State of the Art

Abstract: A review of evolutionary algorithms (EAs) with applications to antenna and propagation problems is presented. EAs have emerged as viable candidates for global optimization problems and have been attracting the attention of the research community interested in solving real-world engineering problems, as evidenced by the fact that very large number of antenna design problems have been addressed in the literature in recent years by using EAs. In this paper, our primary focus is on Genetic Algorithms (GAs), Particle Swarm Optimization (PSO), and Differential Evolution (DE), though we also briefly review other recently introduced nature-inspired algorithms. An overview of case examples optimized by each family of algorithms is included in the paper.

Design of UAVs-Based 3D Antenna Arrays for a Maximum Performance in Terms of Directivity and SLL

Abstract: This paper presents a design of UAVs-based 3D antenna arrays for a maximum performance in terms of directivity and side lobe level (SLL). This paper illustrates how to model the UAVs formation flight using 3D nonuniform antenna arrays. This design of 3D antenna arrays considers the optimization of the positions of the antenna elements to model the UAVs formation flight. In this case, a disk patch antenna is chosen to be used as element in each UAV. The disk patch antenna is formulated by the well-known cavity model. The synthesis process is carried out by the method of Differential Evolution for Multiobjective Optimization (DEMO). Furthermore, a comparison of the performance of 3D nonuniform antenna arrays is provided with respect to the most conventional arrays (circular, planar, linear, and the cubic) for UAVs formation flight.

The RF Energy Harvesting Antennas Operating in Commercially Deployed Frequency Bands: A Comparative Study

Abstract: This paper deals with suitable antennas for energy harvesting, which is a growing research field due to the utilization of nowadays ubiquitous and abundant RF energy. Four types of basic antenna structures suitable for harvesting applications, namely, the patch antenna, slot antenna, modified inverted F antenna, and dielectric resonator antenna, are compared from the viewpoint of reflection coefficient, efficiency, radiation patterns, and dimensions. The frequencies of interest were chosen so that they cover several main wireless systems operating between 0.8 GHz and 2.6 GHz, that is, GSM, UMTS, and WiFi.

State-of-the-Art Developments of Acoustic Energy Transfer

Abstract: Acoustic energy transfer (AET) technology has drawn significant industrial attention recently. This paper presents the reviews of the existing AETs sequentially, preferably, from the early stage. From the review, it is evident that, among all the classes of wireless energy transfer, AET is the safest technology to adopt. Thus, it is highly recommended for sensitive area and devices, especially implantable devices. Though, the efficiency for relatively long distances (i.e., >30 mm) is less than that of inductive or capacitive power transfer; however, the trade-off between safety considerations and performances is highly suitable and better than others. From the presented statistics, it is evident that AET is capable of transmitting 1.068 kW and 5.4 W of energy through wall and in-body medium (implants), respectively. Progressively, the AET efficiency can reach up to 88% in extension to 8.6 m separation distance which is even superior to that of inductive and capacitive power transfer.

Assessment of Measurement Distortions in GNSS Antenna Array Space-Time Processing

Abstract: Antenna array processing techniques are studied in GNSS as effective tools to mitigate interference in spatial and spatiotemporal domains. However, without specific considerations, the array processing results in biases and distortions in the cross-ambiguity function (CAF) of the ranging codes. In space-time processing (STP) the CAF misshaping can happen due to the combined effect of space-time processing and the unintentional signal attenuation by filtering. This paper focuses on characterizing these degradations for different controlled signal scenarios and for live data from an antenna array. The antenna array simulation method introduced in this paper enables one to perform accurate analyses in the field of STP. The effects of relative placement of the interference source with respect to the desired signal direction are shown using overall measurement errors and profile of the signal strength. Analyses of contributions from each source of distortion are conducted individually and collectively. Effects of distortions on GNSS pseudorange errors and position errors are compared for blind, semi-distortionless, and distortionless beamforming methods. The results from characterization can be useful for designing low distortion filters that are especially important for high accuracy GNSS applications in challenging environments.

Radar Coincidence Imaging for Off-Grid Target Using Frequency-Hopping Waveforms

Abstract: Radar coincidence imaging (RCI) is a high-resolution staring imaging technique without the limitation of the target relative motion. To achieve better imaging performance, sparse reconstruction is commonly used. While its performance is based on the assumption that the scatterers are located at the prediscretized grid-cell centers, otherwise, off-grid emerges and the performance of RCI degrades significantly. In this paper, RCI using frequency-hopping (FH) waveforms is considered. The off-grid effects are analyzed, and the corresponding constrained Cramer-Rao bound (CCRB) is derived based on the mean square error (MSE) of the “oracle” estimator. For off-grid RCI, the process is composed of two stages: grid matching and off-grid error (OGE) calibration, where two-dimension (2D) band-excluded locally optimized orthogonal matching pursuit (BLOOMP) and alternating iteration minimization (AIM) algorithms are proposed, respectively. Unlike traditional sparse recovery methods, BLOOMP realizes the recovery in the refinement grids by overwhelming the shortages of coherent dictionary and is robust to noise and OGE. AIM calibration algorithm adaptively adjusts the OGE and, meanwhile, seeks the optimal target reconstruction result.

The Effect of Refractivity on Propagation at UHF and VHF Frequencies

Abstract: This paper is using weather parameters to investigate the effect of refractivity on propagation in the first kilometer of the atmosphere over the English Channel for a long transhorizon path of 140 km. Different refractivity profiles are constructed based on meteorological data taken from the UK Meteorological Office in order to investigate the effects of refractivity on propagation. The analysis is made for the hourly experimental path loss between the transmitter and receiver obtained from the experimental setup comprised of two communication links. The frequency of operation of the first link is 2015 MHz and that of the second link is 240 MHz. Parabolic equation method is modelled to get an hourly modelled path loss corresponding to each hourly experimental path loss to be analyzed for the said communication links. The correlation between the modelled path loss and experimental path loss is computed for refractivity distribution recommended by the ITU and predicted profiles. It is inferred from the simulated and experimental results that little or no influence exists by the evaporation duct upon path loss at 2015 MHz specifically for a long path of 140 km over the sea.

Band-Notched UWB Antenna with Switchable and Tunable Performance

Abstract: A band-notched UWB antenna is presented, which can switch between two notch bands and tune the central frequency simultaneously. It is the first time that the switchable and tunable behaviours are combined together in band-notched UWB antennas. In the band-notched structure, PIN diodes are used to switch the lower and upper frequency bands, while varactors could vary the central frequency of each notch band continuously. Measurement results show that the notch bands could switch between 4.2 GHz and 5.8 GHz when the state of varactors is fixed, and the ranges of tuning are 4.2–4.8 GHz and 5.8–6.5 GHz when the state of PIN diodes is ON and OFF, respectively.

Millimeter-Wave Microstrip Antenna Array Design and an Adaptive Algorithm for Future 5G Wireless Communication Systems

Abstract: This paper presents a high gain millimeter-wave (mmW) low-temperature cofired ceramic (LTCC) microstrip antenna array with a compact, simple, and low-profile structure. Incorporating minimum mean square error (MMSE) adaptive algorithms with the proposed 64-element microstrip antenna array, the numerical investigation reveals substantial improvements in interference reduction. A prototype is presented with a simple design for mass production. As an experiment, HFSS was used to simulate an antenna with a width of 1 mm and a length of 1.23 mm, resonating at 38 GHz. Two identical mmW LTCC microstrip antenna arrays were built for measurement, and the center element was excited. The results demonstrated a return loss better than 15 dB and a peak gain higher than 6.5 dBi at frequencies of interest, which verified the feasibility of the design concept.

Fractal Reflectarray Antennas: State of Art and New Opportunities

Abstract: Fractal geometries are appealing in all applications where miniaturization capabilities are required, ranging from antennas to frequency selective surfaces (FSS) design. Recently, some fractal patches configurations, giving low losses, reduced size, and quite good phase ranges, have been proposed for the design of reflectarray unit cells. This paper reviews existing fractal-based reflectarrays, highlighting their benefits and limitations. Furthermore, a comprehensive analysis of an innovative reflectarray unit cell, using a fractal-shaped fixed-size patch, is presented. The miniaturization capabilities of the Minkowski fractal shape are fully exploited to obtain a compact cell offering quite good phase agility, by leaving unchanged the patch size and acting only on the fractal scaling factor. Experimental validations are fully discussed on a realized 10 GHz cell. This is subsequently adopted to synthesize various reflectarray prototypes offering single or multiple-beam capabilities over a quite large angular region (up to 50 degrees). Finally, experimental validations on a realized elements prototype are presented to demonstrate the wide angle beam-pointing capabilities as well as a quite large bandwidth of about 6%.

Improved OAM-Based Radar Targets Detection Using Uniform Concentric Circular Arrays

Abstract: Without any relative moves or beam scanning, the novel Orbital-Angular-Momentum- (OAM-) based radar targets detection technique using uniform concentric circular arrays (UCCAs) shows the azimuthal estimation ability, which provides new perspective for radar system design. However, the main estimation method, that is, Fast Fourier Transform (FFT), under this scheme suffers from low resolution. As a solution, this paper rebuilds the OAM-based radar targets detection model and introduces the multiple signal classification (MUSIC) algorithm to improve the resolution for detecting targets within the main lobes. The spatial smoothing technique is proposed to tackle the coherent problem brought by the proposed model. Analytical study and simulation demonstrate the superresolution estimation capacity the MUSIC algorithm can achieve for detecting targets within the main lobes. The performance of the MUSIC algorithm to detect targets not illuminated by the main lobes is further evaluated. Despite the fact that MUSIC algorithm loses the resolution advantage under this case, its estimation is more robust than that of the FFT method. Overall, the proposed MUSIC algorithm for the OAM-based radar system demonstrates the superresolution ability for detecting targets within the main lobes and good robustness for targets out of the main lobes.

Wideband, Low-Profile, Dual-Polarized Slot Antenna with an AMC Surface for Wireless Communications

Abstract: A wideband dual-polarized slot antenna loaded with artificial magnetic conductor (AMC) is proposed for WLAN/WIMAX and LTE applications The slot antenna mainly consists of two pairs of arrow-shaped slots along the diagonals of the square patch Stepped microstrip feedlines are placed orthogonally to excite the horizontal and vertical polarizations of the antenna To realize unidirectional radiation and low profile, an AMC surface composed of 7 × 7 unit cells is designed underneath a distance of ( being the wavelength in free space at 225 GHz) from the slot antenna Both the dual-polarized slot antenna and the AMC surface are fabricated and measured Experimental results demonstrate that the proposed antenna achieves for both polarizations a wide impedance bandwidth (return loss 10 dB) of 367%, operating from 196 to 284 GHz The isolation between the two input ports keeps higher than 29 dB whereas the cross-polarization levels basically maintain lower than −30 dB across the entire frequency band High front-to-back ratios better than 22 dB and a stable gain higher than 8 dBi are obtained over the whole band

FPGA Implementation of Real-Time Compressive Sensing with Partial Fourier Dictionary

Abstract: This paper presents a novel real-time compressive sensing (CS) reconstruction which employs high density field-programmable gate array (FPGA) for hardware acceleration. Traditionally, CS can be implemented using a high-level computer language in a personal computer (PC) or multicore platforms, such as graphics processing units (GPUs) and Digital Signal Processors (DSPs). However, reconstruction algorithms are computing demanding and software implementation of these algorithms is extremely slow and power consuming. In this paper, the orthogonal matching pursuit (OMP) algorithm is refined to solve the sparse decomposition optimization for partial Fourier dictionary, which is always adopted in radar imaging and detection application. OMP reconstruction can be divided into two main stages: optimization which finds the closely correlated vectors and least square problem. For large scale dictionary, the implementation of correlation is time consuming since it often requires a large number of matrix multiplications. Also solving the least square problem always needs a scalable matrix decomposition operation. To solve these problems efficiently, the correlation optimization is implemented by fast Fourier transform (FFT) and the large scale least square problem is implemented by Conjugate Gradient (CG) technique, respectively. The proposed method is verified by FPGA (Xilinx Virtex-7 XC7VX690T) realization, revealing its effectiveness in real-time applications.

A Compact Novel Three-Port Integrated Wide and Narrow Band Antennas System for Cognitive Radio Applications

Abstract: The design of a three-port radiating structure, integrating wide and narrow band antennas for cognitive radio applications, is presented. It consists of a UWB antenna for spectrum sensing and two narrow band antennas for wireless communication integrated on the same substrate. The UWB antenna covers the complete UWB spectrum (3.1 GHz to 10.6 GHz) approved by FCC. In the two narrow band antennas, each antenna presents dual bands. In particular, the first narrowband antenna resonates at 6.5 GHz, covering the frequency band between 6.36 GHz and 6.63 GHz, and at 9 GHz, covering the frequency band between 8.78 GHz and 9.23 GHz, presenting minimum return loss values of 28.3 dB at 6.5 GHz and 20.5 dB at 9 GHz, respectively. Similarly, the second one resonates at 7.5 GHz, covering the frequency band between 7.33 GHz and 7.7 GHz, and at 9.5 GHz, covering the frequency band between 9.23 GHz and 9.82 GHz, presenting minimum return loss values of 19.6 dB at 7.5 GHz and 28.8 dB at 9.5 GHz, respectively. Isolation among the three antennas is less than −20 dB over the UWB frequency spectrum. These antennas are realized on a FR4 substrate of dimensions 30 mm × 30 mm × 1.6 mm. Experimental results show a good agreement between the simulated and measured results.

Joint User Scheduling and MU-MIMO Hybrid Beamforming Algorithm for mmWave FDMA Massive MIMO System

Abstract: The large bandwidth and multipath in millimeter wave (mmWave) cellular system assure the existence of frequency selective channels; it is necessary that mmWave system remains with frequency division multiple access (FDMA) and user scheduling. But for the hybrid beamforming system, the analog beamforming is implemented by the same phase shifts in the entire frequency band, and the wideband phase shifts may not be harmonious with all users scheduled in frequency resources. This paper proposes a joint user scheduling and multiuser hybrid beamforming algorithm for downlink massive multiple input multiple output (MIMO) orthogonal frequency division multiple access (OFDMA) systems. In the first step of user scheduling, the users with identical optimal beams form an OFDMA user group and multiplex the entire frequency resource. Then base station (BS) allocates the frequency resources for each member of OFDMA user group. An OFDMA user group can be regarded as a virtual user; thus it can support arbitrary MU-MIMO user selection and beamforming algorithms. Further, the analog beamforming vectors employ the best beam of each selected MU-MIMO user and the digital beamforming algorithm is solved by weight MMSE to acquire the best performance gain and mitigate the interuser inference. Simulation results show that hybrid beamforming together with user scheduling can greatly improve the performance of mmWave OFDMA massive MU-MIMO system.

Connectivity Analysis of Millimeter-Wave Device-to-Device Networks with Blockage

Abstract: We consider device-to-device (D2D) communications in millimeter-wave (mm Wave) for the future fifth generation (5G) cellular networks. While the mm Wave systems can support multiple D2D pairs simultaneously through beamforming with highly directional antenna arrays, the mm Wave channel is significantly more susceptible to blockage compared to microwave; mm Wave channel studies indicate that if line-of-sight (LoS) paths are blocked, reliable mm Wave communications may not be achieved for high data-rate applications. Therefore, assuming that an outage occurs in the absence of the LoS path between two wireless devices by obstructions, we focus on connectivity of the mm Wave D2D networks. We consider two types of D2D communications: direct and indirect schemes. The connectivity performances of the two schemes are investigated in terms of (i) the probability to achieve a fully connected network and (ii) the average number of reliably connected devices . Through analysis and simulation, we show that, as the network size increases, and decrease. Also, and decrease, when the blockage parameter increases. Moreover, simulation results indicate that the hybrid direct and indirect scheme can improve both and up to about 35% compared to the nonhybrid scheme.

High Performance Robust Adaptive Beamforming in the Presence of Array Imperfections

Abstract: A high performance robust beamforming scheme is proposed to combat model mismatch. Our method lies in the novel construction of interference-plus-noise (IPN) covariance matrix. The IPN covariance matrix consists of two parts. The first part is obtained by utilizing the Capon spectrum estimator integrated over a region separated from the direction of the desired signal and the second part is acquired by removing the desired signal component from the sample covariance matrix. Then a weighted summation of these two parts is utilized to reconstruct the IPN matrix. Moreover, a steering vector estimation method based on orthogonal constraint is also proposed. In this method, the presumed steering vector is corrected via orthogonal constraint under the condition where the estimation does not converge to any of the interference steering vectors. To further improve the proposed method in low signal-to-noise ratio (SNR), a hybrid method is proposed by incorporating the diagonal loading method into the IPN matrix reconstruction. Finally, various simulations are performed to demonstrate that the proposed beamformer provides strong robustness against a variety of array mismatches. The output signal-to-interference-plus-noise ratio (SINR) improvement of the beamformer due to the proposed method is significant.

Cavity-Backed Angled-Dipole Antennas for Millimeter-Wave Wireless Applications

Abstract: A cavity-backed angled-dipole antenna is proposed for millimeter-wave wireless applications The angled-dipole radiator is built on both sides of an RT/Duroid 5880 substrate () and fed by a parallel-plate transmission line The cavity-backed reflector is utilized to improve the radiation characteristics of the angled dipole, such as gain, back-radiation, symmetric pattern, and similar 3 dB beamwidth in the - and -planes The design, with a cavity aperture of , results in a dB bandwidth of 267–306 GHz, a gain of 66–80 dB, and a similar 3 dB beamwidth of approximately 70° for both the - and -planes Eight-element linear arrays with the proposed antenna having a center-to-center spacing of 56 mm are characterized, fabricated, and measured By applying nonuniform power distribution across excitations, the array achieves a scan angle up to 40° and a sidelobe level below −15 dB

Design of a Compact Quad-Band Slot Antenna for Integrated Mobile Devices

Abstract: In order to incorporate different communication standards into a single device, a compact quad-band slot antenna is proposed in this paper. The proposed antenna is composed of a dielectric substrate, T-shaped microstrip patch with a circle slot and an inverted L-slot, and a comb-shaped ground on the back of the substrate. By adopting these structures, it can produce four different bands, while maintaining a small size and a simple structure. Furthermore, a prototype of the quad-band antenna is designed and fabricated. The simulated and measured results show that the proposed antenna can operate over the 1.79–2.63 GHz, 3.46–3.97 GHz, 4.92–5.85 GHz, and 7.87–8.40 GHz, which can cover entire PCS (Personal Communications Service, 1.85–1.99 GHz), UMTS (Universal Mobile Telecommunications System, 1.92–2.17 GHz), WCDMA (wideband code-division multiple access, 2.1 GHz), Bluetooth (2.4–2.48 GHz), WiBro (Wireless Broad band access service, 2.3–3.39 GHz), WLAN (Wireless Local Area Networks, 2.4/5.2/5.8 GHz), WiMAX (Worldwide Interoperability for Microwave Access, 2.5/3.5/5.5 GHz), and X-band SATcom applications (7.9~8.4 GHz). The proposed antenna is particularly attractive for mobile devices integrating multiple communication systems.

Design of Asymmetrical Relay Resonators for Maximum Efficiency of Wireless Power Transfer

Abstract: This paper presents a new design method of asymmetrical relay resonators for maximum wireless power transfer. A new design method for relay resonators is demanded because maximum power transfer efficiency (PTE) is not obtained at the resonant frequency of unit resonator. The maximum PTE for relay resonators is obtained at the different resonances of unit resonator. The optimum design of asymmetrical relay is conducted by both the optimum placement and the optimum capacitance of resonators. The optimum placement is found by scanning the positions of the relays and optimum capacitance can be found by using genetic algorithm (GA). The PTEs are enhanced when capacitance is optimally designed by GA according to the position of relays, respectively, and then maximum efficiency is obtained at the optimum placement of relays. The capacitance of the second resonator to th resonator and the load resistance should be determined for maximum efficiency while the capacitance of the first resonator and the source resistance are obtained for the impedance matching. The simulated and measured results are in good agreement.

Substrate Integrated Slot Array Antenna with Required Radiation Pattern Envelope

Abstract: A substrate integrated slot array antenna with a prescribed radiation pattern is investigated in this paper. To meet the requirement of a certain standard radiation pattern envelope, the array configuration and the element excitation coefficient should be considered together. An efficient and systematic method is proposed to determine the element number and element weights in a planar array. After that, the geometrical dimension of the substrate integrated slot array can be synthesized. As an example, a -band 16 × 22 slot array antenna based on the substrate integrated waveguide (SIW) technology is designed, fabricated, and measured. Its radiation pattern can meet the class 3 antenna radiation pattern envelope of the European Telecommunications Standards Institute (ETSI) standard pattern. Experimental results are in good agreement with simulated ones.

Minimum Lens Size Supporting the Leaky-Wave Nature of Slit Dipole Antenna at Terahertz Frequency

Abstract: We designed a slit dipole antenna backed by an extended hemispherical silicon lens and investigated the minimum lens size in which the slit dipole antenna works as a leaky-wave antenna. The slit dipole antenna consists of a planar feeding structure, which is a center-fed and open-ended slot line. A slit dipole antenna backed by an extended hemispherical silicon lens is investigated over a frequency range from 0.2 to 0.4 THz with the center frequency at 0.3 THz. The numerical results show that the antenna gain responses exhibited an increased level of sensitivity to the lens size and increased linearly with increasing lens radius. The lens with the radius of 1.2 is found to be the best possible minimum lens size for a slit dipole antenna on an extended hemispherical silicon lens.

Optically Controlled Reconfigurable Filtenna

Abstract: This work is regarding the development of a novel antenna called optically controlled reconfigurable filtenna, which is based on the integration of a broadband printed antenna with a bandpass reconfigurable RF filter. The filter is designed by applying defected microstrip structure (DMS) technique and positioned in printed antenna feeding line in order to keep the same size of the original antenna. The filtenna bandwidth is optically reconfigurable by using two photoconductive silicon switches excited by CW laser at 808 nm. Numerical results rely on independent and switchable operational modes through the 2.4 and 5.1 GHz ISM bands, whereas measurements demonstrate two reconfigurable modes based on single-band/dual-band operation over the same frequency bands. The proposed device is validated by theoretical, numerical, and experimental results.

A Banach Space Regularization Approach for Multifrequency Microwave Imaging

Abstract: A method for microwave imaging of dielectric targets is proposed. It is based on a tomographic approach in which the field scattered by an unknown target (and collected in a proper observation domain) is inverted by using an inexact-Newton method developed in Banach spaces. In particular, the extension of the approach to multifrequency data processing is reported. The mathematical formulation of the new method is described and the results of numerical simulations are reported and discussed, analyzing the behavior of the multifrequency processing technique combined with the Banach spaces reconstruction method.

Iterative GA Optimization Scheme for Synthesis of Radiation Pattern of Linear Array Antenna

Abstract: This research has proposed the iterative genetic algorithm (GA) optimization scheme to synthesize the radiation pattern of an aperiodic (nonuniform) linear array antenna. The aim of the iterative optimization is to achieve a radiation pattern with a side lobe level (SLL) of ≤−20 dB. In the optimization, the proposed scheme iteratively optimizes the array range (spacing) and the number of array elements, whereby the array element with the lowest absolute complex weight coefficient is first removed and then the second lowest and so on. The removal (the element reduction) is terminated once the SLL is greater than −20 dB (>−20 dB) and the elemental increment mechanism is triggered. The results indicate that the proposed iterative GA optimization scheme is applicable to the nonuniform linear array antenna and also is capable of synthesizing the radiation pattern with SLL ≤ −20 dB.

A Wearable Wireless Energy Link for Thin-Film Batteries Charging

Abstract: A wireless charger for low capacity thin-film batteries is presented. The proposed device consists of a nonradiative wireless resonant energy link and a power management unit. Experimental data referring to a prototype operating in the ISM band centered at 434 MHz are presented and discussed. In more detail, in order to facilitate the integration into wearable accessories (such as handbags or suitcases), the prototype of the wireless energy link was implemented by exploiting a magnetic coupling between two planar resonators fabricated by using a conductive fabric on a layer of leather. From experimental data, it is demonstrated that, at 434 MHz, the RF-to-RF power transfer efficiency of the link is approximately 69.3%. As for the performance of the system as a whole, when an RF power of 7.5 dBm is provided at the input port, a total efficiency of about 29.7% is obtained. Finally, experiments performed for calculating the charging time for a low capacity thin-film battery demonstrated that, for RF input power higher than 6 dBm, the time necessary for recharging the battery is lower than 50 minutes.