Showing papers in "IEEE Antennas and Propagation Magazine in 2017"

Current Misuses and Future Prospects for Printed Multiple-Input, Multiple-Output Antenna Systems [Wireless Corner]

Abstract: In the past six years or so, the number of scientific articles and conference papers providing possible multiple-input, multiple-output (MIMO) antenna system solutions has noticeably increased. Flagship conferences on antennas and propagation have recently had multiple sessions addressing MIMO antenna systems and their applications. The importance of such antenna systems lies in the magnitude of their application in current wireless devices and gadgets, and this thrust will continue because fourth-generation (4G) and the upcoming fifth-generation (5G) wireless standards rely heavily on MIMO technology. But throughout the years, and up until now, a wide range of publications still suffer from some major misconceptions and unclear understanding of the fundamental aspects while designing, characterizing, and evaluating such multiantenna systems.

For Satellites, Think Small, Dream Big: A review of recent antenna developments for CubeSats.

Abstract: Advances in modern technology have aided the development of a class of miniaturized satellites called SmallSats that typically weigh less than 500 kg. Key members of this family are CubeSats. CubeSats can weigh as little as 1.33 kg, with a typical volume of 10 ? 10 ? 10 cm3. Their potential has motivated the scientific community to revisit existing spacecraft technologies to make them suitable for CubeSats.

A Deployable High-Gain Antenna Bound for Mars: Developing a new folded-panel reflectarray for the first CubeSat mission to Mars.

Abstract: This article describes the development of a deployable high-gain antenna (HGA) for the proposed Mars Cube One (MarCO) CubeSat mission to Mars. The antenna is a new folded-panel reflectarray (FPR) designed to fit on a 6U (10 ? 20 ? 34 cm3) CubeSat bus and support 8.425-GHz Mars-to-Earth telecommunications. The FPR provides a gain of 29.2 dBic with right-hand circular polarization (RHCP). Small stowage volume is a key advantage of the FPR design, as it only consumes ~4% of the usable spacecraft payload volume with a mass of less than 1 kg.

Near-Field-Focused Microwave Antennas: Near-field shaping and implementation.

Abstract: Focusing the electromagnetic field radiated by an antenna at a point in the antenna near-field (NF) region is a wellknown technique to increase the electromagnetic power density in a size-limited spot region close to the antenna aperture. This article encompasses the basic working principles and the applications of the NF-focused (NFF) microwave antennas as well as the synthesis procedures suggested for the NF shaping around the focal point and the technologies currently used for their implementation.

Path-Loss Modeling for Wireless Sensor Networks: A review of models and comparative evaluations.

Abstract: Propagation models are used to abstract the actual propagation characteristics of electromagnetic waves utilized for conveying information in a compact form (i.e., a model with a small number of parameters). The correct modeling of propagation and path loss is of paramount importance in wireless sensor network (WSN) system design and analysis [1]. Most of the important performance metrics commonly employed for WSNs, such as energy dissipation, route optimization, reliability, and connectivity, are affected by the utilized propagation model. However, in many studies on WSNs, overly simplistic and unrealistic propagation models are used. One of the reasons for the utilization of such impractical propagation models is the lack of awareness of experimentally available WSN-specific propagation and path-loss models. In this article, necessary succint background information is given on general wireless propagation modeling, and salient WSN-specific constraints on path-loss modeling are summarized. Building upon the provided background, an overview of the experimentally verified propagation models for WSNs is presented, and quantitative comparisons of propagation models employed in WSN research under various scenarios and frequency bands are provided.

Electromagnetic Tomography for Detection, Differentiation, and Monitoring of Brain Stroke: A Virtual Data and Human Head Phantom Study.

Abstract: Brain stroke is one of the leading causes of death and disability worldwide [1]. It can be classified as ischemic stroke (i-stroke), e.g., blood flow is restricted by a blood clot, or hemorrhagic stroke (h-stroke), e.g., a bleeding in the brain. Approximately 80% of total stroke cases are ischemic. The most common treatment for i-stroke to date is the use of thrombolytics: drugs that dissolve the blood clots. The clinical decision to apply a thrombolytic should be made within 3-4.5 h from the onset of the stroke symptoms (e.g., [2]), and it relies on imaging methods such as computed tomography (CT) and magnetic resonance imaging (MRI). Further evaluation of stroke evolution is done mainly by imaging to assess the extent of the ischemic injury and to correlate with the functional behavior of the patient. However, to date there is no accurate way to provide reliable information about the key components of i-stroke physiology that include the position and size of the acute stroke (arterial occlusion), the core infarct region that contains irreversibly injured tissues, and the ischemic penumbra, i.e., the tissue that could potentially be restored by rapid revascularization [1], [3].

Fraunhofer and Fresnel Distances : Unified derivation for aperture antennas.

Abstract: In this article, the size of antenna Fresnel and Fraunhofer field regions are systematically derived starting from a general phase factor representation of the scalar diffraction theory. This is done by first expressing the phase of an arbitrary aperture field in a Taylor series in terms of a small parameter and then by subsequently imposing appropriate conditions for the Fresnel and Fraunhofer regions.

A Step Toward 5G in 2020: Low-cost OTA performance evaluation of massive MIMO base stations.

Abstract: Massive multiple-input, multiple-output (MIMO) is seen as an enabling technology to fulfill dramatic improvements in spectral efficiency for fifth-generation (5G) deployment in 2020. For massive MIMO systems, the learning loop from early-stage prototype design to final-stage performance validation is expected to be slow and ineffective. There is a strong need to evaluate massive MIMO base station (BS) performance with over-the-air (OTA) methods. Until now, such OTA solutions have not been discussed for massive MIMO BS systems.

Numerical Modeling and High-Speed Parallel Computing: New Perspectives on Tomographic Microwave Imaging for Brain Stroke Detection and Monitoring.

Abstract: This article deals with microwave tomography for brain stroke imaging using state-of-the-art numerical modeling and massively parallel computing. Iterative microwave tomographic imaging requires the solution of an inverse problem based on a minimization algorithm (e.g., gradient based) with successive solutions of a direct problem such as the accurate modeling of a whole-microwave measurement system. Moreover, a sufficiently high number of unknowns is required to accurately represent the solution. As the system will be used for detecting a brain stroke (ischemic or hemorrhagic) as well as for monitoring during the treatment, the running times for the reconstructions should be reasonable. The method used is based on high-order finite elements, parallel preconditioners from the domain decomposition method and domain-specific language with the opensource FreeFEM++ solver.

Compressive Sensing as Applied to Inverse Problems for Imaging: Theory, Applications, Current Trends, and Open Challenges.

Abstract: Compressive sensing (CS) is currently one the most active research fields in information engineering and science. The flexibility, robustness, accuracy, effectiveness, and sound theory behind such a paradigm have motivated a great interest in developing and applying CS to many domains, including inverse scattering. Unfortunately, electromagnetic imaging problems have some unique theoretical features that prevent a straightforward exploitation of CS tools. Therefore, suitable CS-based strategies must be considered in such a framework.

Wearable Textile Antennas: Examining the effect of bending on their performance.

Abstract: This article presents a study on the effect of bending on the performance of a rectangular textile-patch antenna operating at a 2.4-GHz industrial, scientific, and medical (ISM) band. The substrate of the antenna was made from denim textile, and the conducting layers were made from a copper and nickel plated polyester fabric. A parametric study was made to determine the influence of an antenna bending around its length and width on its performance parameters in chest, leg, arm, or wrist integration for wireless body-area network (WBAN) scenarios. Results were obtained from bench and anechoic chamber measurements and compared with simulation results. The prototype presents a maximum gain of approximately 4 dBi and 70° of half-power beamwidth (HPBW) in the flat position. When subjected to a wrist equivalent bending, the gain decreases by 2 dB, HPBW has an increase of about 25°, and front-to-back radiation ratio decreases. Mean and standard deviation parameters as a function of bending curvature were calculated from parametric simulations.

The Deep-Space Network Telecommunication CubeSat Antenna: Using the deployable Ka-band mesh reflector antenna.

Abstract: In the near future, CubeSats will be deployed beyond low-Earth orbit (LEO) to perform scientific tasks in deep space. To do so, these CubeSats will need high-gain antennas (HGAs) that fit in a highly confined volume. In this article, we present an innovative, deployable Ka-band antenna that folds in a 1.5-U (10 ? 10 ? 15 cm3) stowage volume suitable for 6U (10 ? 20 ? 30 cm3)-class CubeSats. This antenna is designed for telecommunication and is compatible with NASA's deep-space network (DSN) at Ka-band frequencies (i.e., uplink: 34.2-34.7 GHz; downlink: 31.8-32.3 GHz). Calculations and measurements show that 42.0-dBi gain and 57% aperture efficiency are obtained at 32 GHz. We thoroughly describe the mechanical deployment mechanism because it is a critical component of the deployable Cube-Sat antenna. This challenging new design evolved from our previous design that only provided linear polarization and a single-frequency band.

Conformal Integrated Solar Panel Antennas: Two effective integration methods of antennas with solar cells.

Abstract: This article reviews two conformal antenna designs that can be integrated with CubeSats' solar panels without competing for surface real estate. The first type of antenna is of slot geometry so that the antennas can be integrated around solar cells, and the second type is optically transparent patches that can be placed on top of solar cells. Detailed design philosophy, prototypes, measurements, and assessment of interaction between the antennas and solar cells are presented. As larger CubeSats have sufficient panel area to host antenna arrays, a subwavelength reflectarray, with optimal overall properties both in terms of gain and optical transparency, is presented. The overall transparency and aperture efficiency of the reflectarray are higher than 90% and 40%, respectively, making it a promising solution as a high-gain conformal CubeSat antenna.

Microwave Tomography for Industrial Process Imaging: Example Applications and Experimental Results.

Abstract: This article describes the implementation of microwave tomography for industrial process applications. Microwave tomography for industrial process imaging has different requirements from that for medical imaging. In addition to spatial resolution, high temporal resolution or real-time imaging is also important for high-speed processes, flows, or rapid reactions. Depending on the specific application, both quantitative imaging and qualitative imaging may be needed. Qualitative imaging would be sufficient to display distributions, patterns, or shapes, which may be adequate for some applications. Quantitative imaging would, however, be more informative, giving images with quantitative dielectric contrast or permittivity values from which other physical parameters, such as density, moisture content, and phase fraction, may be derived. With the microwave tomography approach described, several example applications in industrial processes are demonstrated, and a number of experimental imaging results are presented.

Transparent and Nontransparent Microstrip Antennas on a CubeSat: Novel low-profile antennas for CubeSats improve mission reliability.

Abstract: This article reviews the development of some novel low-profile antennas for CubeSats. The integrated antennas were developed using microstrip-antenna technology, and the antennas were designed to be low profile while having minimal (or zero) blockage of the solar panels on the CubeSat. Two types of designs were investigated: 1) transparent antennas, which are placed above the solar panels (supersolar) and 2) nontransparent antennas, which are placed below the solar panels (subsolar). For past: using transparent metal and using a wire mesh design. The transparent metal indium tin oxide has a comparatively high sheet impedance, which makes an antenna design less efficient. Also, there is a tradeoff between conductivity and transparency [6]. However, a highly conductive thin mesh structure has demonstrated a reasonable efficiency and a high transparency [7]. The substrate must then also be transparent, e.g., glass or quartz.

Surface Plasmons\/Polaritons, Surface Waves, and Zenneck Waves: Clarification of the terms and a description of the concepts and their evolution.

Abstract: The first objective of this article is to explain what surface plasmons and surface plasmon polaritons are. The term surface plasmons (SPs) was first coined in the middle of the 20th century to study the response of thin metal foils at petahertz frequencies when subjected to fast electron bombardment. SPs are coherent electron oscillations that exist at the interface between two materials where the real part of the permittivity changes sign across the interface. When an SP couples with a photon, the resulting hybrid excitation is called a surface plasmon polariton (SPP). SP refers to the charge oscillations alone, while SPP refers to the entire excitation of the charge oscillations and the electromagnetic (EM) wave. Under the right conditions, the photon can excite a longitudinal wave of electrons in the metal. The second objective is to describe the evolution of these concepts over the years and illustrate their relation to a surface wave and not to a Zenneck wave. Both Zenneck and surface waves are transverse magnetic (TM) waves. The surface waves thus cannot be excited by transverse EM (TEM) waves but rather by an electron beam that can be effectively generated by a source of electrons or a quasiparticle such as an evanescent wave, which can tunnel through the medium and thus excite the electrons. This electron wave produces its own EM wave, and this plasmonic wave is confined to a very small region near the interface. Hence, SPP is a surface wave with a longitudinal field component that propagates at the interface between a metal and a dielectric at petahertz when the conditions are right and can propagate along the metal-dielectric interface at a wavelength that is shorter than that of incident light until its energy is lost either via absorption in the conductivity of the metal or through radiation in free space. The longitudinal surface wave of an SPP is sometimes wrongly associated with a Zenneck wave. A Zenneck wave is produced at the zero of the reflection coefficient of a plane incident TM wave (at the Brewster angle of incidence) on an air-dielectric interface, whereas surface waves are produced when the TM reflection coefficient is infinite. Both the Zenneck wave and the surface wave are TM waves and are nonradiating, as they have, in general, exponentially decaying fields with distance. For the Zenneck wave, the evanescent transverse field components do not change appreciably with frequency (because the phenomenon of Brewster angle is independent of frequency), whereas for a surface wave, with an increase of the frequency the wave is more closely coupled to the surface. This property makes it possible to distinguish between these two evanescent waves. SPP is generally coupled with Raman scattering and not with Rayleigh scattering. These points are illustrated in the remainder of the article. Hence, surface plasmons/polaritrons are surface waves that are the solution of Maxwell's equations unless perhaps there is a resonant Raman scattering, which is equivalent to exciting the structure with an incident frequency corresponding to the electronic absorption bands, as illustrated in "A Survey of the Various Natures of Light Scattering."

Antenna Design Using Binary Differential Evolution: Application to discrete-valued design problems.

Abstract: Several antenna design problems are discrete valued. Particle swarm optimization (PSO) and differential evolution (DE) are popular evolutionary algorithms that have been applied to a number of design problems in electromagnetics. However, both PSO and DE are best suited for continuous search spaces. Therefore, to apply these to binary-coded combinatorial optimization problems, binary versions of the aforementioned algorithms must be used. In this article, we introduce a design technique based on novel binary DE (NBDE). The main benefit of NBDE is reserving the DE updating strategy to binary space.

Degrees of Freedom and Maximum Directivity of Antennas: A bound on maximum directivity of nonsuperreactive antennas.

Abstract: We derive a general fundamental directivity limitation formula that applies to nonsuperreactive antennas of any size that fit within a minimum sphere of any given radius rmin. The derivation is done by using a new concept: the degrees of freedom (DoF) of the field radiated by arbitrary sources within the minimum sphere must be twice the maximum directivity. The formula converges to the known bound of the directivity for large rmin. For small spheres, it becomes equal to three, i.e., 4.8 dBi, which is the directivity of the Huygens source. The transition region between these two limiting cases is determined by counting the most significant spherical modes at the surface of the minimum sphere. This is not trivial, because spherical modes have a gradual cutoff when their order approaches krmin. Therefore, we use a weighted summation where the weighting factor is inversely proportional to the radiation-Q of the modes. This extends the DoF from a discrete to continuous function of the minimum sphere radius. The final maximum directivity is similar to a previously published heuristic limit. The formulas are compared to results for measured antennas with large directivity and superdirectivity.

Broadband Dual-Polarized Dual-Dipole Planar Antennas: Analysis, Design, and Application for Base Stations

Abstract: In this article, we propose a compact ±45° dual-polarized dual-dipole (DPDD) antenna for second-, third-, and fourth-generation (2G/3G/4G) long-term evolution (LTE) base stations. The DPDD antenna consists of two perpendicularly crossed dual-dipole elements. Each dual-dipole element is directly fed by a coaxial cable. Two dual-dipole elements are printed on the same substrate, making the DPDD antenna planar and compact. Due to the coupling between two crossed dual-dipole elements, the DPDD antenna can achieve a broad bandwidth of 51% for a return loss greater than 15 dB (1.61-2.71 GHz) with a high isolation of 30 dB. The dual-polarized antenna has a gain of 9 dBi and a halfpower beamwidth (HPBW) of 65 ± 5° for ±45° polarization with a flat metallic reflector. For applications in LTE700/GSM850/900 base stations, a new artificial magnetic conductor (AMC) surface is introduced to replace the metallic reflector. It is shown that the antenna height can be significantly lowered from 105 mm (0.29λ0.83, where λ0.83 is the freespace wavelength at the frequency of 0.83 GHz) for a metallic reflector to 31.52 mm (0.087λ0.83) for an AMC surface while a broad bandwidth of 52% (0.68-1.16 GHz) is still achieved. The broadband ±45° DPDD antenna is described in the "Broadband ±45° DPDD Antenna" section, and the ±45° DPDD antenna with an AMC surface is demonstrated in the "DPDD Antenna with an AMC Surface" section.

A Design of an Origami Reconfigurable QHA with a Foldable Reflector [Antenna Applications Corner]

Abstract: This article presents a design of an origami reconfigurable circularly polarized quadrifilar helical antenna (QHA) with a foldable reflector that can operate in K, Ka, and extremely high-frequency (EHF) bands. A 10:1 scale prototype of the proposed antenna is built and validated through measurements and simulations.

Optimization of a Printed UWB Antenna: Application of the invasive weed optimization algorithm in antenna design.

Abstract: This article presents a general approach to design and optimize printed ultrawideband (UWB) antennas by using invasive weed optimization (IWO), a well-known global optimization algorithm. To achieve the required radiation parameters over a wide bandwidth, a frequency-related cost function with optimal weighting coefficients is suggested. Two prototypes of the optimized antenna have been manufactured and examined. The experimental outcomes show good agreement with the simulated ones that validate the proposed optimization approach. The optimized antenna has a compact size of 50 mm × 50 mm. The operational bandwidth of the antenna for S 11 <; -10 dB, from both measurement and simulation, is 150%, based on the center frequency of 6.4 GHz (1.6-11.2 GHz), which also covers the UWB (3.1-10.6 GHz) applications. The time-domain response of the antenna was also investigated by measurement of the group delay. Finally, the efficiency of the optimized antenna in terms of bandwidth, size, and gain are compared with a number of previously proposed designs. Comparison results show that the optimized antenna outperforms other designs cited. The experimental outcomes in frequency as well as the time domain show that the antenna is suitable for use in UWB or other communication systems.

The Challenges of Measuring Integrated Antennas at Millimeter-Wave Frequencies [Measurements Corner]

Abstract: The increasing demand for radar sensors and the wide distribution of handheld communication devices push the development of low-cost components with a small form factor. One approach to achieve smaller, low-cost devices is the integration of the required components on a monolithic microwaveintegrated circuit (MMIC). At frequencies above 100 GHz, passive components are small enough to be integrated onto a chip, and the advances in semiconductor technology make it possible to build active components that can operate at millimeter (mm)-wave frequencies [1], [2]. The available bandwidths of several gigahertz at mm-wave frequencies offer high data rates for communication devices or high resolution for remote-sensing applications. By integrating the radio-frequency (RF) components and the antennas, lossy off-chip transitions can be avoided, thus limiting the required connections to the power supply and baseband signals.

Compact, Microstrip-Based Folded-Shorted Patches: PCB antennas for use on microsatellites.

Abstract: A compact printed circuit board (PCB) antenna for use on microsatellites was designed and measured for ultrahigh-frequency (UHF) low-data-rate communication applications. The miniaturized and fully integrated antenna structure consists of an array of four linearly polarized folded-shorted-patch elements placed in a sequential rotation with a coupler-based feeding circuit to achieve circular polarization (CP). The dimensions of the fabricated and measured PCB antenna are 0.2l0 x 0.2l0 x 0.05l0. The measured gain values are greater than 0.4 dBiC at 398 MHz. A design procedure for the microstrip-based antenna is provided along with a transmission line model that accurately predicts the operation and resonant frequency of the miniaturized patches. Numerical calculations agree with the full-wave simulations as well as the antenna measurements, which demonstrate functionality. The miniaturized, low-cost antenna unit can be useful for space communications and other surveillance applications as well as network formations of small satellites where broad-beam patterns with low gain values are required for adequate coverage.

An Embedded Lightweight Folded Printed Quadrifilar Helix Antenna: UAV telemetry and remote control systems.

Abstract: An embedded folded, printed, quadrifilar helix antenna (FPQHA) with a wide-angle coverage for unmanned aerial vehicles (UAVs) telemetry and remote control systems is presented in this article. The novelty of this design is that the FPQHA needs to be designed carefully due to UAV tail dimensions and weight constraints while maintaining a high performance to be integrated in the inner part of the UAV tail fuselage to reduce aerodynamic drag. The radiating terminal, formed by a folded, printed, four-helix, radiating section and a compact feeding network, is designed to provide left-handed, circular polarization (LHCP). The complete design offers a very homogeneous pattern in azimuth with a very good axial-ratio (AR) level over a wide range of elevation angles. The use of low-loss and lightweight materials is also an advantage of this design. The wide radiation pattern favors its use for multielement communication systems. Finally, the antenna performance results are obtained mounted inside a UAV tail platform.

Robotic Through-Wall Imaging: Radio-Frequency Imaging Possibilities with Unmanned Vehicles.

Abstract: Using electromagnetic waves for sensing has been of interest to the research community for many years. More recently, sensing with lower frequencies, such as with radio waves and even with Wi-Fi, has become of interest due to factors like safety and availability of the transceivers. In particular, there has been a considerable interest in using radio-frequency (RF) signals to sense and obtain information about the environment in various contexts, such as imaging, localization, tracking, and occupancy estimation [1]-[10]. See-through imaging (also known as through-wall imaging) has, in particular, been of considerable interest to the research community. The ability to see through occluded objects can be beneficial to many applications, such as search and rescue, surveillance and security, archaeological discovery, detection/classification of occluded objects, and medical applications. Despite great interest in this area, however, see-through imaging is still a considerably challenging problem, especially with everyday RF signals.

Antenna Arrays in the Time Domain: An introduction to timed arrays.

Abstract: The term phased array comes from the time-harmonic/steady-state analysis of antenna arrays. These arrays use phase shifters to electronically steer the main beam. Phase shifters cause beam squint and pulse dispersion for wide-band signals, so time-delay units are needed to correct these errors. Adaptive and reconfigurable arrays also have time-dependent responses. In addition, time-dependent spurious signals arise due to nonlinearities in amplifiers. This article presents several time-varying issues related to antenna arrays that should not be modeled by the time-harmonic representation of an array. Future antenna arrays will be wideband and time varying, so antenna arrays will have to be designed in the time domain.

Optical Antennas: Controlling Electromagnetic Scattering, Radiation, and Emission at the Nanoscale

Abstract: The emerging field of optical nanoantennas has been extending the reach of traditional antenna technology to the realms of photonics, nanotechnology, and quantum electrodynamics. In this article, we review the basic concepts of nanoantennas while highlighting similarities and differences with their low-frequency counterparts. We discuss how several concepts from traditional antenna technology, e.g., the antenna input impedance, can be translated to optical frequencies, and examine the new phenomena and engineering opportunities enabled by the material platform available at these frequencies. In this article, particular attention is devoted to different kinds of plasmonic nanoantennas (nanodipoles, nanoloops, and nanopatches) and to systematic approaches to control and enhance their performances, especially for impedance matching and directivity enhancement. We also show how linear and nonl inear plasmonic nanoantennas represent an ideal platform to realize anomalous and extreme forms of classical and quantum light-matter interactions, including artificial optical magnetism, spontaneous emission enhancement, and anomalous coupling between quantum emitters. As antenna concepts are increasingly appreciated and used in the design of nanophotonic devices and systems, we believe that the exciting field of optical antennas holds promise for large technological and scientific impact in the coming years.

Comparison of Fabrication Techniques for Flexible UHF RFID Tag Antennas [Wireless Corner]

Abstract: The astonishing boom of radio-frequency identification (RFID) technology is stimulating plenty of new RFID-based industrial applications. Consequently, in the very near future, an almost unlimited number of RFID tags could be embedded into manufactured goods of various shapes, assets, and machineries to enable their communication abilities. As a result, prototyping techniques of RFID tags on flexible substrates are becoming more crucial. In this article, four different techniques suitable for prototyping flexible tags are briefly explained and tested from many points of view: ease of use, processing time, cost, tag sensitivity, radiation pattern, impedance, and robustness of the realized prototype. Characterization methods and experimental setups are presented, and two tag layouts, one commercial and one appositely designed, are used to compare the different techniques.

Antenna Array Failure Correction [Antenna Applications Corner]

Abstract: Because the possibility of array element failure during operation cannot be ruled out [1], selfrecoverable antenna array systems have recently been receiving considerable attention in modern radar technology. Thus, an approach to maintaining the radiation properties of the array by resynthesizing the excitations of the functioning elements is preferable to replacing failed elements. This article describes the implementation of two optimization algorithms to find a suitable solution for optimal beam pattern. The algorithms, based on metaheuristics, are called particle swarm optimization (PSO) and bacteria foraging optimization (BFO). Of these two techniques, BFO is relatively new to the antenna community. We compare the performance of both algorithms in terms of their ability to suppress the sidelobe level (SLL) and null steering in failed antenna arrays to achieve a graceful degradation in the radiation pattern.

A Multiband, Mutipolarization Shared-Aperture Antenna: Design and evaluation.

Abstract: A compact, shared-aperture antenna (SAA) configuration consisting of various planar antennas embedded into a single footprint is presented in this article. An L-probefed, suspended-plate, horizontally polarized antenna operating in an 900-MHz band; an aperture-coupled, vertically polarized, microstrip antenna operating at 4.2-GHz; a 2 × 2 microstrip patch array operating at the X band; a low-side-lobe level (SLL), corporate-fed, 8 × 4 microstrip planar array for synthetic aperture radar (SAR) in the X band; and a printed, single-arm, circularly polarized, tilted-beam spiral antenna operating at the C band are integrated into a single aperture for simultaneous operation. This antenna system could find potential application in many airborne and unmanned aircraft vehicle (UAV) technologies. While the design of these antennas is not that critical, their optimal placement in a compact configuration for simultaneous operation with minimal interference poses a significant challenge to the designer. The placement optimization was arrived at based on extensive numerical fullwave optimizations.