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Charge‐programmed 3D printing enables the fabrication of 3D electronics with lightweight and high precision via selective patterning of metals. This selective metal deposition is catalyzed by Pd nanoparticles that are specifically immobilized onto the charged surface and promises to fabricate a myriad of complex electronic devices with self‐sensing, actuation, and structural elements assembled in a designed 3D layout. However, the achievable property space and the material‐performance correlation of the charge‐programmed printing remain unexplored. Herein, a series of photo‐curable resins are designed for unveiling how the charge and crosslink densities synergistically impact the nanocatalyst‐guided selective deposition in catalytic efficiency and properties of the 3D printed charge‐programmed architectures, leading to high‐quality 3D patterning of solid and liquid metals. The findings offer a wide tunability of the structural properties of the printed electronics, ranging from stiff to extreme flexibility. Capitalizing on these results, the printing and successful application of an ultralight‐weight and deployable 3D multi‐layer antenna system operating at an ultrahigh‐frequency of 19 GHz are demonstrated. [ABSTRACT FROM AUTHOR]

Beam-steerable Risley prism antennas (RPAs) typically require at least three separated components, including a stationary feed source and two independently rotatable gradient-phase-shift surfaces. In this letter, we propose a simplified two-component RPA configuration that employs a gradient-phase feed source and a gradient-phase transmitarray. The proposed configuration is validated by a novel circularly polarized (CP) RPA in the $K$ -band through simulations. It consists of an $\text{8}\times \text{8}$ gradient-phase CP patch array feed and a 10 cm diameter CP transmitarray. The total height of this system is 14.6 mm, which is less than one wavelength at 19 GHz. A left-hand CP beam scan from broadside to $\text{55}^\circ$ is demonstrated. The simulated RPA achieved a broadside directivity of 22.3 dBi at 19 GHz (42.7% aperture efficiency) and a 3 dB directivity bandwidth of 9.2%. [ABSTRACT FROM AUTHOR]

Conventional transmitarray antennas are designed to produce a directional pattern with the beam peak in a single direction when the feed is placed at a distinct location. A real-life application requiring conical beam scanning necessitates the development of antennas with patterns that sweep out a cone in space through successive excitation of feeds placed at multiple locations along the body of the revolution ring focus. In this communication, we propose transmitarrays as an antenna solution that can achieve the conical beam sweep. Compared to the previously reported transmitarrays, the development of an off-axis-fed transmitarray for conical beam scanning requires significant advancements regarding the synthesis and optimization of the off-axis-fed transmitarray. A novel synthesis algorithm is presented based on the optimization of the feed location and a modified transmitarray phase compensation. To validate the approach, an 18 cm transmitarray with a thickness of 0.8 cm operating at 13.4 GHz is designed, simulated, prototyped, and measured. Predictions obtained by full-wave simulations agree well with the measured results. The conical beam scanning capability of the transmitarray is demonstrated through measurements taken with the feed placed at five locations within the ring focus. [ABSTRACT FROM AUTHOR]

In this article, we present systematic modeling and optimization strategies for embroidery electrotextile patch antennas, including material characterization, detailed modeling, stitch density study, and surrogate-based optimization. A detailed full-wave model that accounts for the complex embroidery features is proposed, with the effects of stitch density analyzed and validated through measurements for both rectangular and E-shaped patch antennas. A textile tailored surrogate optimization technique is then implemented to accelerate the computationally expensive full-wave evaluation for the detailed full-wave model, saving almost an order of magnitude of the computation time compared with canonical optimization. The methodologies presented in this article provide a pathway for both improved accuracy and efficiency in designing embroidery electrotextile patch antennas. [ABSTRACT FROM AUTHOR]

Low-cost and lightweight CubeSats have opened new possibilities to realize Internet of Space (IoS), a vision that aims to provide global network access, particularly for remote areas. A key challenge for IoS realization is the development of an antenna that can meet the gain, bandwidth, and polarization requirements for IoS while complying with the small form factor of CubeSats. The challenge is further magnified by the need to dynamically reconfigure the antenna’s beam location to maintain connectivity as the satellite orbits. This work addresses these challenges by proposing a beam steerable reflectarray antenna that can potentially be integrated with CubeSats to enable IoS. A novel reflectarray unit cell containing multiple Archimedean spiral arms is designed to support broadband circularly polarized (CP) operation, and its operational principle is discussed in depth. The unit cell provides four states of phase shift that are electronically switchable, allowing the reflectarray to achieve the required aperture phase for the desired beam scan. Representative reflectarray prototypes are designed, fabricated, and measured. CP beam scan up to 60° in the plane of offset across the targeted frequency band of 17.8–20.2 GHz is achieved. [ABSTRACT FROM AUTHOR]

With the increasing interest in the applications of large deployable reflector antennas operating at high frequencies, the requirement on the reflector surface accuracy becomes more demanding. Thermal effects inevitably cause certain reflector surface distortions, thus degrading the overall antenna performance. This paper introduces a novel reflector surface distortion compensation technique using a subreflectarray and presents detailed discussions. A microstrip reflectarray is used as a subreflector, illuminated by a primary feed. By properly adjusting the additional phase shift provided by the subreflectarray, the aperture phase errors caused by the main reflector surface distortions are compensated, resulting in a considerably improved antenna performance. As an example, a distorted 20-m offset parabolic reflector antenna operating at X-band is successfully compensated by a subreflectarray, and the simulation results are compared with those obtained by array feed and shaped subreflector compensation techniques. The microstrip subreflectarray is low-profile, lightweight, and cost-effective. Only one primary feed is required, and a reconfigurable design can be achieved if electronically reconfigurable reflectarray elements are adopted. Index Terms--Distortion compensation, reflectarray, reflector antenna.

In adaptive beamforming by compact arrays, the excitation amplitude and phase of each array element require dynamic optimization for controlling the radiation pattern at different angular sectors. If the objective function of adaptive beamformer is defined by some properties other than the deterministic properties of arrays such as directivity or signal-to-noise ratio, evolutionary optimization is advantageously implemented to minimize the objective function. Nevertheless, the convergence time of most of the evolutionary optimization methods exponentially increases by the number of array elements $N$. For large $N$ , the above convergence issue slows down the beamforming agility. To improve the above inefficiency, we first express the array factor by a Schelkunoff polynomial of order $N - 1$. Second, a discrete optimization method like genetic algorithm optimally factorizes the polynomial into two polynomials of orders $N - 1 - P$ and $P$ , where $N - 1 - P \ge P$. Third, the locations of zeros of these polynomials are optimized across the visible region by a continuous optimization method like particle swarm optimization to attain the desired objective function. When these two polynomials are multiplied, the resultant polynomial of order $N - 1$ demonstrates improved features with respect to the original polynomial of order $N - 1$ in sensitivity, sidelobe level, and convergence. Representative examples include airborne radars. [ABSTRACT FROM AUTHOR]

Current spaceborne wind scatterometers have shown failure due to mechanical wear from moving parts used to conically scan a directive beam. In order to eliminate the risk of mechanical rotation failure, an antenna design with no moving parts that achieve the conical beam sweep is desirable. In this article, a lightweight, 3-D-printed, inhomogeneous lens antenna is presented as an all-electronic alternative. Compared to the previous on-axis fed lenses, the real-life application requiring conical scanning necessitates significant developments regarding the synthesis, optimization, and prototyping of the off-axis fed lens. The lens antenna is designed using curved-ray geometrical optics coupled to particle swarm optimization to determine the optimum lens surface shapes and material inhomogeneity while obtaining a design with minimum volume and therefore mass. An 18 cm lens is designed using this approach. Instructions on how to 3-D-print the inhomogeneous lens are given using a unit cell design, which permits additive manufacturing using fused deposition modeling (FDM) techniques. The lens is measured for far-field pattern performance at various locations along with the ring-shaped focus of the azimuthally symmetric lens. The measurements agree well with predictions obtained by full-wave simulations. These all-electronic alternatives are expected to prolong the lifetime of future spaceborne wind scatterometers. [ABSTRACT FROM AUTHOR]

This paper describes the design of a reconfigurable reflectarray element using commercially available radio frequency micro-electromechanical system (RF MEMS) switches. The element consists of a microstrip patch on the top surface and a slot with an actuated variable length in the ground plane. RF MEMS switches are mounted on the slot to electronically vary the slot length by actuating the switches and thus obtaining the desired phase response. Waveguide measurements and High Frequency Structure Simulator (HFSS) simulations are used to characterize the reflectarray element. The four MEMS switches element gives 10 independent states with a phase swing of 150[degrees] and a loss variation from 0.4 dB to 1.5 dB at 2 GHz (more switches can provide larger phase shift). The loss is mainly attributed to the dielectric loss and the conductor loss, which occur due to the relatively strong electric fields in the substrate region below the patch and the large currents on the top surface of the patch, respectively, close to the patch resonance. Detailed analysis is performed to characterize the effect of the switches by taking into consideration the switch model and wire bonding effects. Index Terms--Patch, radio frequency micro-electromechanical system (RF MEMS), reflectarray, slot.

Near-field measurements typically require both amplitude and phase information to correctly predict the far-field. Unfortunately, there are situations in which the phase data is not available or impractical to obtain. That is why there has been a need for the development of phaseless techniques. Up until now, a number of remarkable solutions to this problem have been proposed by the researcher in different disciplines. Unfortunately, the complete vectorial representation of the field is not investigated in depth. The evaluated cases are usually linearly polarized and only the dominant polarization is investigated while the cross polarized field is usually neglected. This paper addresses the polarization issue in a two-component approach and then proposes a solution to the problem. A searching mechanism, for the incorporation of an appropriate initial guess, is integrated into the well-known, iterative Fourier technique (plane-to-plane) to enhance the algorithm response. Then, using two sets of measured orthogonal information data gathered by two linearly and orthogonally polarized probes, it is shown that with the aid of only a single point amplitude measurement, the polarization characteristics of the antenna can be extracted up to an inherent ambiguity of the right- and left-handedness. In order to have an assessment of the applicability of the proposed method, both linearly and circularly polarized antennas are simulated. Additionally, the method of extracting the polarization from the phaseless data is also verified through a bi-polar near-field measurement. Index Terms--Iterative Fourier technique OFT), near-field measurements, phaseless measurements, polarization sensing.

A novel design methodology is presented for correlator antenna arrays in radio astronomy applications. In order to characterize the spatial-filter-like performance of a correlator array, an analyzer is developed to calculate its u-v coverage and synthesized beam, along with the capability to simulate the Earth rotation effect and the image retrieval process. On the other hand, particle swarm optimization (PSO) is applied to determine the locations of antenna elements in typical open-ended and closed array configurations (such as the 'Y' and the Reuleaux triangle), in order to achieve either the maximum u-v coverage or a synthesized beam with the lowest sidelobe level (SLL). Optimized arrays are observed to outperform uniform arrays and representative existing designs. Index Terms--Correlator antenna array, particle swarm optimization, radio astronomy, synthesized beam, u-v coverage.

The conductor and dielectric loss mechanisms in microstrip reflectarray are described using simulation models and waveguide measurements. The dielectric constant and loss tangent variation with frequency is obtained for a particular substrate using existing datasheets. Variable size patch reflectarray element was studied for loss characterization. The effect of these losses is characterized and the potential cause for the loss phenomenon is provided. It is observed that the dielectric loss and copper loss occur near the patch resonance due to strong electric fields in the substrate region below the patch and the large currents on the top surface of the patch, respectively. Index Terms--Conductor loss, dielectric loss, reflectarray.

A back-to-back reflector antenna system with reduced moment of inertia is proposed in order to address the demanding problem of supporting large reflector antennas on spinning platforms. The configuration provides additional potential advantages, such as reducing the spinning speed by half for a given sampling rate when both back-to-back reflectors are utilized. Geometrical parameters of the reflector are determined such that the moment of inertia of the rotating system is reduced. It is shown that these back-to-back reflectors suffer from a high cross-pol level in the asymmetrical plane due to the large feed offset angle. Two different methods are explored to alleviate the high cross-pol level problem. In the first method, a sub reflector is utilized to minimize the cross-pol level by satisfying the Mizugutchi condition. In the second method, a tri-mode matched feed horn is suggested to achieve a similar result. The suppressed cross-pol level puts forward the gravitationally balanced back-to-back reflector antenna systems as a potential candidate for future spacecraft antennas on spinning platforms. Index Terms--Matched feeds, reflector antennas, remote sensing, spinning platforms.

The microwave observatory of subcanopy and subsurface (MOSS) is a mission concept for a spaceborne synthetic aperture radar (SAR) system that provides global observations of soil moisture under substantial vegetation cover (exceeding 20 kg/[m.sup.2]) and at useful depths (1-5 m). The concept was developed and a number of new required technologies were demonstrated through a National Aeronautics and Space Administration Earth Science Technology Office Instrument Incubator Program project. This very high frequency (VHF)/ultrahigh frequency (UHF) polarimetric SAR is designed to provide 7-10-day observations of soil moisture at 1-km resolution. The rapid repeat cycle mandates swath widths in the range of 300-400 km, which must be realized by a 30-m-long antenna. Conventional array implementations would result in a mass of more than 4000 kg, whereas with the technology proposed and demonstrated in this project, the total antenna mass is less than 500 kg. The antenna concept is a dual-stacked patch array feed illuminating a 30-m mesh reflector to synthesize the long apertures and achieve the wide swath. The feed system prototype was fabricated and its performance demonstrated. Other major project components were: 1) system-level SAR and mission design; 2) demonstration of science data and products, using a tower-based VHF/UHF radar; 3) spacecraft and mesh reflector antenna mechanical design; 4) developing mitigation strategies for ionospheric effects; and 5) assessing frequency interference effects. Experimental science data were generated from the tower radar for soil moisture profiling in Arizona and for forest penetration in Oregon. The soil moisture products were demonstrated through an integrated inversion-processing algorithm. This paper summarizes the results from the MOSS project and demonstrates the feasibility of the spaceborne mission. Index Terms--Canopy penetrating radar, large-aperture antennas, radar remote sensing, soil moisture, subsurface radar.

Reflector antennas with complex mesh weave patterns are numerically analyzed by using extended physical optics (PO) combined with the periodic method of moments (MoM). The method applies the periodic MoM with Rao-Wilton-Glisson (RWG) basis and testing functions. It calculates the transmission coefficient matrix (T-matrix) of the realistic, complex weave pattern of the planar mesh, in order to calculate the modified PO current on the mesh reflector. When analyzed, the planar grid mesh is found to be compatible with the commonly used wire-grid model. The modified PO current on the locally planar mesh is implemented on the curved reflector surface for the diffraction analysis of the mesh reflector antennas. The far-field pattern of the offset parabolic antenna with grid mesh, modelled using periodic MoM, agreed well with those obtained from the wire-grid model. T-matrix calculated from the tabulated T-matrix data using the interpolation method is sufficiently accurate and compares well with the one calculated using the direct method, allowing users to choose one of the T-matrix calculation methods depending on the problem. The analysis of the mesh reflectors with two different complex weave patterns (single Satin and single Atlas at Ka band) is performed to exemplify the application of the extended PO/periodic MoM algorithm. It is shown that differences were observed in cross-polarization discrimination (XPD) for circular polarization operations depending on the weave patterns. This result demonstrates the usefulness of the proposed technique in accurate performance prediction of mesh reflector antennas with complex weave patterns. Index Terms--Mesh reflecting surfaces, periodic method of moments, physical optics, reflector antenna, spaceborne antenna.

In order to enforce particles to search inside the solution space of interest during the optimization procedure, various boundary conditions are currently used in particle swarm optimization (PSO) algorithms. The performances, however, vary considerably with the dimensionality of the problem and the location of the global optimum in the solution space. In this paper, different boundary conditions are categorized into two groups, namely, restricted and unrestricted, according to whether the errant particles are relocated inside the allowable solution space or not. Moreover, efforts are made to explore different hybrid unrestricted boundary conditions by introducing the favorable characteristics of the reflecting and damping boundary conditions into the existing invisible boundary condition. The performances of the boundary conditions are tested based on both mathematical benchmark functions and a real-world electromagnetic problem: the optimization of a 2-D 16-element array antenna. Simulation results are examined from both the effectiveness and efficiency of the algorithm. Comparisons show that the unrestricted boundary conditions are more efficient when the global optimum is inside the boundary of the solution space, and the damping boundary condition is more robust and consistent when the global optimum is close to the boundary. Index Terms--Array antenna, evolutionary algorithm, optimization methods, particle swarm optimization (PSO).

The particle swarm optimization (PSO) is a recently developed evolutionary algorithm (EA) based on the swarm behavior in the nature. This paper presents recent advances in applying a versatile PSO engine to real-number, binary, single-objective and multiobjective optimizations for antenna designs, with a randomized Newtonian mechanics model developed to describe the swarm behavior. The design of aperiodic (nonuniform and thinned) antenna arrays is presented as an example for the application of the PSO engine. In particular, in order to achieve an improved peak sidelobe level (SLL), element positions in a nonuniform array are optimized by real-number PSO (RPSO). On the other hand, in a thinned array, the ON/OFF state of each element is determined by binary PSO (BPSO). Optimizations for both nonuniform arrays and thinned arrays are also expanded to multiobjective cases. As a result, nondominated designs on the Pareto front enable one to achieve other design factors than the peak SLL. Optimized antenna arrays are compared with periodic arrays and previously presented aperiodic arrays. Selected designs fabricated and measured to validate the effectiveness of PSO in practical electromagnetic problems. Index Terms--Aperiodic antenna array, binary optimization, multiobjective, optimization methods, particle swarm optimization (PSO), real-number optimization, single-objective.

Realizing antenna arrays that preserve channel capacity in multiple-input multiple-output (MIMO) radio communications is a challenge because of the detrimental effects of mutual coupling. The fact that mutual coupling becomes more pronounced as antenna spacing decreases is therefore a critical issue with compact arrays used in portable MIMO radios. The contributions made in this paper include the realization of compact MIMO arrays designed to preserve channel capacity and the characterization of these compact arrays' performance in field measurements using MIMO radios. A multiport metric is used to characterize the compact arrays in a way that more appropriately measures array performance under MIMO signalling conditions than the traditional scattering matrix characterization. Field measurements show the extent and proportion of the effect that correlation and radiation efficiency have on MIMO channel capacity. The compact arrays' strong performance in field measurements is explained by their ability to preserve the MIMO channel's eigenstructure. Results also show that mutual coupling prevents channel capacity from scaling linearly with the number of antennas. Guidelines for compact MIMO array design are given with supporting results from field measurements. Index Terms--Antenna arrays, channel capacity, mobile antennas, multiple-input multiple-output (MIMO) systems.

This paper presents the verification of the equivalent strip width for a cylindrical wire for mesh reflector antennas with experimental and numerical analysis and compares waveguide and plane-wave simulations. For experimental purposes, the transmission and reflection characteristics of copper strips and copper wires were measured. For numerical analysis, a model of the experimental setup was designed and simulated in High-Frequency Structure Simulator (HFSS). Comparing the measurement and HFSS simulated results confirmed that the numerical model was accurate. Using HFSS, it was verified that the equivalent strip width for a cylindrical wire is almost twice (~1.89) the wire diameter (for an infinitely thin strip) for typical mesh reflector structures. A periodic strip model was simulated both in HFSS and periodic Method of Moments (MoM) using the plane-wave incidence at different angles and the transmission and reflection characteristics were determined. The effects of the thickness of the strip, angle of incidence, and the spacing between the adjacent strips on the equivalence between the strip width and wire diameter were also studied. As the center to center strip spacing increases beyond 1.5[lambda], the equivalent factor [beta] (strip width/wire diameter) approaches the classical factor of 2. Index Terms--Mesh, reflector antennas, strip, waveguide simulations wire.

A reconfigurable frequency-selective electromagnetic filter implemented by integrating hard magnetic materials with microelectromechanical systems (MEMS) provides a new variation of reconfigurable frequency-selective surfaces (FSS). By incorporating magneticaily actuated dipole elements that are capable of being tilted away from the supporting surface, we can tune the FSSs operating frequency without having to physically alter the dimensions of the dipole elements. The 25 x 25 array of microactuators used in this work each consist of a 896 x 168 x 30 [micro][m.sup.3] ferromagnetic plate made of 40Co-60Ni, layered with a 1-[micro]m-thick conductor (Au), attached to a pair of 400 x 10 x 1 [micro][m.sup.3] polysilicon torsion beams, suspended just above the supporting substrate. The high remanent magnetization of the ferromagnetic material allows for relatively small magnetic fields (~ 2.1 kA/m) to induce significant angular deflections (~ 40[degrees]). This innovative reconfigurable FSS design has successfully demonstrated electromagneticsignal diplexing and tuning its resonant frequency over a bandwidth of 2.7 GHz at a frequency of 85 GHz. [1452] Index Terms--Frequency-selective surfaces, magnetic micro-electromechanical systems (MEMS), tunable filter.

This paper introduces a new technique which calculates the reflection coefficient for the plane wave incident on planar periodic structures. The method referred to as spectral finite-difference time-domain (SFDTD) replaces the conventional single-angle incident wave, with a constant transverse wavenumber (CTW) wave. Because the transverse wavenumbers are constant, the fields have no delay in the transverse plane (x - y plane), and PBC (periodic boundary condition) can be directly implemented in the time domain for both oblique and normal incident waves. The stability criterion for this new FDTD technique is angle-independent and therefore this method works well for incident angles close to grazing ([theta] = 90[degrees]) as well as normal incident ([theta] = 0[degrees]). This shows the efficiency of the method compared to other available FDTD techniques for the same purpose that force a more restricted stability criterion as angles turns to grazing. The validity of this method is verified by comparing the reflection coefficient calculated by this method with the analytical results of a grounded slab. The results of this technique are also compared with method of moments for a periodic array of metallic patches and a good agreement is observed. A periodic array of metallic patches above a PEC plate is analyzed and the reflection coefficient is calculated over a wide frequency band for angles varying from 0[degrees] to close to 90[degrees]. Index Terms--Finite-difference time-domain (FDTD) methods, periodic structures, spectral domain techniques.

Reconfigurable reflectarrays have been designed with patch elements which can vary the reflected phase by varying the height of the patches. These patches have been designed using a periodic method of moments simulation. Reflectarrays incorporating elements of varying heights have been built and tested. The first design is a 33 element array comprised of stacked patches which operates at 7.31 GHz. The second design is a 120-element dipole array over a ground plane which operates at 5.2 GHz. Microelectrical, mechanical systems actuation technology could be used to implement these designs and a potential concept is suggested. Index Terms--Microelectrical, mechanical systems (MEMS) utilization, phase shifters, reflectarray, reflector antenna.

There is a growing demand for impulse radiating antennas (IRAs) to receive and transmit short pulses. The basic concepts of IRA are reviewed and the far-field pattern versus frequency of an ideal IRA is characterized based on the fundamental properties of IRA. It is shown that the transmitted pulse is ideally in the form of a time derivative of the input pulse. The physical optics simulation results show that the far-field characteristics of a parabolic reflector are very close to an ideal IRA if it is fed properly. The reflector IRA was constructed, analyzed and measured at UCLA. The near-field and far-field characteristics of the reflector IRA are studied using both the method of moments (MoM) full-wave simulations and the frequency domain measurements. In this paper, the radiation mechanism of the reflector IRA is studied using a detailed current distribution on the parabolic reflector and the feeding structure at different frequencies. Applying either the calculated current distribution on the reflector IRA or the measured near-field results, it is seen that the aperture field intensity of the parabolic reflector is not the same in the two principle planes and as a result the beam-widths in the two principle planes are different. The far-field patterns of the antenna are measured and the calculated far-field patterns support the measured results. The calculated current distribution results provide a guideline on how to properly change the feeding structure to achieve a more uniform aperture field and increase the antenna radiation efficiency. Index Terms--Antenna measurements, frequency domain analysis, impulse radiating antenna (IRAs), method of moments (MoM), reflector antenna, ultrawide-band antenna.

In this paper, the recently proposed patch antenna with switchable slot (PASS) concept is implemented to design a novel reconfigurable antenna with both frequency and polarization diversities. Using only one switch and a single patch, the antenna operates at 4.20 GHz with right-handed circular polarization and at 4.55 GHz with left-handed circular polarization. The fabricated antenna has both an acceptable return loss and a broadside axial ratio (AR) lower than 2 dB at each operation frequency. The frequency and polarization diversities of this design could potentially improve the reliability of wireless communication systems. Index Terms--Circular polarization, dual-frequency, patch antenna, reconfigurable antenna, switchable slot.

This paper considers the improvement of the feeding structure of the reflector impulse radiating antenna (IRA). Full-wave analysis and measured results of the orthogonal cross-coplanar plate reflector IRA shows that the aperture fields are not uniform. The arm angle is varied as an optimization factor and it is shown that the arm angle of 70[degrees] has the maximum radiation efficiency. The termination load and the arm tapering effects are studied using simulation and measurement results. Furthermore, the effect of radius of circle of symmetry is studied and it is shown that a greater circle provides higher gain. A combination of transverse electromagnetic (TEM) horn antenna and the conical coplanar TEM transmission line is investigated to avoid tiny structure at the focal point and make the connection between the coaxial cable and the feeding arms more convenient. It is shown that a small triangle does not degrade the antenna performance but helps to excite the antenna by a coaxial cable. Finally a combination of the Vivaldi antenna and the coplanar transmission line is introduced to improve the antenna performance. The simulation results for the new antenna show that the antenna efficiency is improved to 45% at the frequency band between 2 GHz to 6 GHz in comparison to the 20.9% for the traditional design and 29.7% for the tapered design. The calculated far-field results of all these antennas are used to radiate a 0.5 ns impulse. The radiated impulse from the Vivaldi fed reflector IRA is 3.55, 2.41, and 2.12 dB higher than the same radiated impulses from the reflector IRA fed by a 45[degrees] traditional feeding arms, 70[degrees] traditional feeding arms, and 70[degrees] tapered feeding arms, respectively. Index Terms--Aperture antennas, impulse radiation antennas (IRAs), method of moments (MoM), ultrawide-band antennas.

There are many stringent demands imposed on the applications of spaceborne antenna systems. One of the most challenging demands is the generation of multiple beams with the ability to scan a very large number of beamwidths. Since the parabolic reflectors have limitations in this application, a 35-m spherical reflector antenna is proposed for a geostationary radar antenna at Ka-band (35.6 GHz) due to its inherent capability of scanning the beams to very large number of beamwidths. The utility of using planar array feeds for correcting spherical phase aberrations is investigated to overcome the performance degradation effects. Two different methodologies are developed for the array excitation coefficients determination based on phase conjugate matching and the results are compared. Using the compensating feed array, the radiation characteristics of the compensated spherical reflector are simulated for no scan and large scan cases and the results are compared with the uncompensated case to show performance improvement. In order to demonstrate the technological readiness of the concept a 1.5-m breadboard model is designed to be built for experimental measurements. Some important mechanical design tolerances and realistic array feed topologies are investigated. The antenna concept developed in this paper is advocated to be used in the next generation of geostationary satellite antenna systems for remote sensing radar applications. Index Terms--Array feed, physical optics, reflector antennas, scanned antennas, spherical reflector.

This paper presents a novel evolutionary optimization methodology for multiband and wide-band patch antenna designs. The particle swarm optimization (PSO) and the finite-difference time-domain (FDTD) are combined to achieve the optimum antenna satisfying a certain design criterion. The antenna geometric parameters are extracted to be optimized by PSO, and a fitness function is evaluated by FDTD simulations to represent the performance of each candidate design. The optimization process is implemented on parallel clusters to reduce the computational time introduced by full-wave analysis. Two examples are investigated in the paper: first, the design of rectangular patch antennas is presented as a test of the parallel PSO/FDTD algorithm. The optimizer is then applied to design E-shaped patch antennas. It is observed that by using different fitness functions, both dual-frequency and wide-band antennas with desired performance are obtained by the optimization. The optimized E-shaped patch antennas are analyzed, fabricated, and measured to validate the robustness of the algorithm. The measured less than--18 dB return loss (for dual-frequency antenna) and 30.5% bandwidth (for wide-band antenna) exhibit the prospect of the parallel PSO/FDTD algorithm in practical patch antenna designs. Index Terms--Finite-difference time-domain (FDTD), parallel computation, particle swarm optimization, patch antenna.

A low profile single dipole antenna that can generate circularly polarized (CP) radiation patterns is proposed in this paper. The CP patterns and low profile configuration are achieved using a specially designed artificial ground plane: a thin grounded slab loaded with periodic rectangular patches. The artificial ground plane exhibits in-phase reflection coefficients with polarization-dependent feature. The radiation mechanism of the antenna is described, and experimental results verify the antenna concept. Index Terms--Artificial ground plane, circular polarization, dipole antenna, low profile.

The focus of this paper is to characterize the effects of periodic and aperiodic surface distortions on the performance of membrane reflector antennas. Since the surface of this class of reflector antennas is very thin, it is susceptible to various types of periodic and aperiodic distortions. The particular antenna dimensions used for this study are similar to the specifications for the JPL/UCLA half scale model of second generation precipitation radar (PR-2) mission reflector. Analytical expressions are introduced to model periodic and aperiodic surfaces and based on these models the effects of distortions on the radiation performance of the antenna are simulated. Aperiodic distortions are more realistic cases of distortions due to the fact that the period of the distortions is not constant through out the reflector surface. For each case, far-field patterns of the reflector are simulated and it is shown that closed-form expressions can then be derived which result in a very efficient computational method to predict some of the unique features of these patterns including location and level of observed grating lobes. Furthermore, based on spatial Fourier analysis of the surface distortion, it is shown that deviation from periodicity in the distortions of reflector surface results in lowering these grating lobes. Parametric studies have been performed to provide design guidelines for acceptable surface behavior for large deployable membrane reflector antennas for future space borne missions. Index Terms--Aperiodic distortions, membrane reflectors, periodic distortions, reflector antennas.

As commercial needs have expanded the functions of the wireless cellular handsets, multiantenna development in one handset has become more and more common. This paper addresses a multiantenna solution for the wireless handset application. Aplanar inverted 'F' antenna (PIFA) was designed as the main antenna of the handset to cover the 800 MHz band (824 MHz-894 MHz) and the 1900 MHz band (1850 MHz-1990 MHz). A side-mounted inverted 'F' antenna (IFA) was designed as the 1575.42 MHz global positioning system (GPS) antenna. The location of the feed/ground pins of both antennas affected not only the total antenna efficiency, but also the polarization of the GPS IFA. The length of the GPS IFA affected the isolation between the two antennas and the specific absorption rate (SAR) of the PIFA at the 1900 MHz band. A three-dimensional efficiency measurement of the prototypes in both free space and against-head position will be presented. Measurement of SAR and its distribution will also be presented to demonstrate the impact of the IFA on the near field of the PIFA. Index Terms--Dual-band, global positioning system (GPS), inverted 'F' antenna (IFA), planar inverted 'F' antenna (PIFA), specific absorption rate (SAR), wireless handset.

This paper focuses on the multiport characterization of antennas. In particular, special attention is given to the cavity backed annular patch antenna (CABAPA) for multipolarization operations. We will show that the reflection coefficient is not the best representative parameter to determine the frequency response of the multiport antenna and its radiation performance. Therefore, we seek a new generalized parameter that conveys the frequency response of multiport antennas. The total active reflection coefficient (TARC) is introduced as the square root of the sum of all incident powers at the ports minus radiated power, divided by the sum of all incident powers at the ports. The TARC is a function of frequency and is a real number between zero and one. With this definition we can characterize the multiport antenna's frequency bandwidth and radiation performance. In this paper, a method for calculating the TARC is detailed for different port excitations directly from the scattering matrix of the antenna and independent of the feeding network. First, the CABAPA is analyzed by the method of moments. Next, the corresponding scattering matrix is employed to calculate the TARC for different polarizations. The calculated results, when compared to the measured results, show good agreement. The measured -10 dB TARC bandwidth of the CABAPA is 30% compared with 68% as measured using only the [s.sub.11]. Index Terms--Broad-band antennas, cavity antennas, microstrip antennas, multiport circuits, polarization, scattering matrices.

A periodic ground plane may be built to either stop the propagation of wave or support a quasi transverse electromagnetic wave along the surface. The former is called a soft surface, and the latter is a hard surface. However, a soft or a hard surface can only be realized in certain frequency and wavenumber regions; therefore, it is important to identify the bandwidth for the surface so that it can be used efficiently. The bandwidth for soft and hard operations of a ground plane has been previously characterized by studying the reflection of normal and oblique plane waves with the real angle of incidence. In this paper, the bandwidth for soft and hard operations of a periodic ground plane is defined as a wavenumber-frequency region in which the complex value of reflection coefficient is inside a circle with the radius of 1/[square root of (2)] and centered at -1 or 1 for soft or hard operation, respectively. This definition gives a unified approach to characterize the bandwidth in both the visible (k.sup.2.sub.x] + [k.sup.2.sub.y] < [k.sup.2.sub.0]) and surface wave (k.sup.2.sub.x] + [k.sup.2.sub.y] < [k.sup.2.sub.0]) regions. The paper uses a newly developed numerical technique referred to as the spectral finite-difference time-domain (FDTD) method, which is capable of calculating the reflection coefficient and impedance of the surface for any given set of wavenumber and frequency of the incident wave including the surface wave region. By using this method, the reflection coefficients and impedances of a corrugated dielectric-lined surface and a mushroom-like EBG are calculated, and the bandwidth for soft, hard, and perfect magnetic conductor like behavior are specified. Index Terms--Electromagnetic band gap (EBG), finite-difference time-domain (FDTD), Floquet theorem, soft/hard surface, spectral, surface impedance.

In this paper, we describe an electromagnetic genetic algorithm (GA) optimization (EGO) application developed for the cluster supercomputing platform. A representative patch antenna design example for commercial wireless applications is detailed, which illustrates the versatility and applicability of the method. We show that EGO allows us to combine the accuracy of full-wave EM analysis with the robustness of GA optimization and the speed of a parallel computing algorithm. A representative patch antenna design case study is presented. We illustrate the use of EGO to design a dual-band antenna element for wireless communication (1.9 and 2.4 GHz) applications. The resulting antenna exhibits acceptable dual-band operation (i.e., better than--10 dB return loss with 5.3 and 7% operating bandwidths at 1.9 and 2.4 GHz) while maintaining a cross-pol maximum field level at least 11 dB below the co-pol maximum. Index Terms--Genetic algorithms, method of moments (MoM), microstrip antenna, optimization, parallel computing.

Antennas implanted in a human body are largely applicable to hyperthermia and biotelemetry. To make practical use of antennas inside a human body, resonance characteristics of the implanted antennas and their radiation signature outside the body must be evaluated through numerical analysis and measurement setup. Most importantly, the antenna must be designed with an in-depth consideration given to its surrounding environment. In this paper, the spherical dyadic Green's function (DGF) expansions and finite-difference time-domain (FDTD) code are applied to analyze the electromagnetic characteristics of dipole antennas and low-profile patch antennas implanted in the human head and body. All studies to characterize and design the implanted antennas are performed at the biomedical frequency band of 402-405 MHz. By comparing the results from two numerical methodologies, the accuracy of the spherical DGF application for a dipole antenna at the center of the head is evaluated. We also consider how much impact a shoulder has on the performance of the dipole inside the head using FDTD. For the ease of the design of implanted low-profile antennas, simplified planar geometries based on a real human body are proposed. Two types of low-profile antennas, i.e., a spiral microstrip antenna and a planar inverted-F antenna, with superstrate dielectric layers are initially designed for medical devices implanted in the chest of the human body using FDTD simulations. The radiation performances of the designed low-profile antennas are estimated in terms of radiation patterns, radiation efficiency, and specific absorption rate. Maximum available power calculated to characterize the performance of a communication link between the designed antennas and an exterior antenna show how sensitive receivers are required to build a reliable telemetry link. Index Terms--Finite difference time domain (FDTD), implanted antenna, maximum available power, microstrip antenna, planar inverted-F antenna (PIFA), specific absorption rate (SAR), spherical dyadic Green's function (DGF).

The particle swarm optimization (PSO), new to the electromagnetics community, is a robust stochastic evolutionary computation technique based on the movement and intelligence of swarms. This paper introduces a conceptual overview and detailed explanation of the PSO algorithm, as well as how it can be used for electromagnetic optimizations. This paper also presents several results illustrating the swarm behavior in a PSO algorithm developed by the authors at UCLA specifically for engineering optimizations (UCLA-PSO). Also discussed is recent progress in the development of the PSO and the special considerations needed for engineering implementation including suggestions for the selection of parameter values. Additionally, a study of boundary conditions is presented indicating the invisible wall technique outperforms absorbing and reflecting wall techniques. These concepts are then integrated into a representative example of optimization of a profiled corrugated horn antenna. Index Terms--Antenna design, genetic algorithm (GA), horn antennas, optimization, particle swarm.