Showing papers in "IEEE Antennas and Wireless Propagation Letters in 2006"

Ant Colony Optimization in Thinned Array Synthesis With Minimum Sidelobe Level

Abstract: The synthesis of unequally spaced large arrays is computationally unapproachable without using an optimization technique. In complex structures, gradient implementations converge to local minima and cannot be used to obtain a desired solution. Thus, global search methods are necessary to get specific design characteristics. In this letter, we propose the ant colony optimization (ACO) as an useful alternative in the thinned array design, using the sidelobe level (SLL) as the desirability parameter. Some examples have been proposed and solved to demonstrate the functionality of this technique for both linear and planar arrays

Time Reversal With MISO for Ultrawideband Communications: Experimental Results

Abstract: Time reversal (TR) communications marks a paradigm shift in ultrawideband (UWB) communications. The system complexity can be shifted from the receiver to the transmitter, which is ideal to some applications. UWB multiple input-single output (MISO) is enabled by the use of the TR scheme. Two basic problems are investigated experimentally using short UWB radio pulses (nanosecond duration). Temporal focusing and increase in collected-energy with the number of antennas are verified. Also, the reciprocity of realistic channels, the cornerstone of TR, is demonstrated perhaps for the first time in electromagnetics

Circular and Elliptical CPW-Fed Slot and Microstrip-Fed Antennas for Ultrawideband Applications

Abstract: This letter presents novel circular and elliptical coplanar waveguide (CPW)-fed slot and mictrostip-fed antenna designs targeting the 3.1?10.6 GHz band. The antennas are comprised of elliptical or circular stubs that excite similar-shaped slot apertures. Four prototypes have been examined, fabricated and experimentally tested, the three being fed by a CPW and the fourth by a microstrip line, exhibiting a very satisfactory behavior throughout the 7.5 GHz of the allocated bandwidth in terms of impedance matching $(hbox VSWR?2)$, radiation efficiency and radiation pattern characteristics. Measured impedance bandwidths of beyond 175% will be presented.

RF Tag Antenna Performance on Various Materials Using Radio Link Budgets

Abstract: Passive radio frequency (RF) tags in the UHF and microwave bands have drawn considerable attention because of their great potential for use in many radio frequency identification (RFID) applications. However, more basic research is needed to increase the range and reliability of a passive RF tag's radio link, particularly when the RF tag is placed onto any lossy dielectric or metallic surface. This paper presents two new useful forms of the radio link budget that describe the power link of an RF tag system when the tag is attached to an object. These radio link budgets are dependent upon the gain penalty, a term which quantifies the reduction in RF tag antenna gain due to material attachment. A series of measurements, or radio assay, was used to measure the far-field gain pattern and gain penalty of several flexible 915 MHz antennas when attached to cardboard, pine plywood, acrylic, deionized water, ethylene glycol, ground beef, and an aluminum slab. It is shown that the gain penalty due to material attachment can result in more than 20 dB of excess loss in the backscatter communication link.

A Band-Notched Ultrawideband Printed Monopole Antenna

Abstract: In this letter, a band-notched ultrawideband (UWB) antenna is presented and the notched-band characteristic is realized by a compact coplanar waveguide (CPW) resonant cell (CCRC). The antenna with a total size of 46 mm $,times,$30 mm operates in a band from 2.67 to over 12 GHz, and shows omnidirectional radiation patterns. Measurements indicate that the antenna presents a notched band from 5.10 to 5.94 GHz for $ VSWR ge 3:1$, which covers the wireless local area network (WLAN) band. The time-domain behaviors and the CCRC are discussed and the group delay is given experimentally. Also, parametric studies are performed numerically in the end.

Blind Calibration and DOA Estimation With Uniform Circular Arrays in the Presence of Mutual Coupling

Abstract: In smart antenna systems, mutual coupling between elements can significantly degrade the performance of array processing algorithms. Based on the special structure of coupling matrix, this letter presents a subspace-based blind calibration method for uniform circular arrays. The method uses the incident signals to carry out both direction of arrival (DOA) estimation and array calibration simultaneously. In addition, the parameter identifiability condition is also provided. Finally, representative computer simulation results are given to demonstrate the effectiveness and behavior of the proposed method

Pair-Matching Method for Estimating 2-D Angle of Arrival With a Cross-Correlation Matrix

Abstract: This letter presents a novel method for pair matching of elevation and azimuth angles in two-dimensional (2-D) angles-of-arrival estimation employing two uniform linear arrays (ULAs). The proposed pair-matching method exploits the cross-correlation matrix of two received signals impinging on each ULA that shows the characteristics of the corresponding angle pairs, and is conducted by combining it with a propagator method. Numerical simulations using L-shaped array geometry revealed that the proposed method provided better robustness over the SNR, angular separation, and number of sources than that of conventional methods.

Bandwidth Enhancement of Wide-Slot Antenna Fed by CPW and Microstrip Line

Abstract: Two printed wide-slot antennas with square patches within an arc-shape slot are proposed in this letter. They are fed by a coplanar waveguide (CPW) and a microstrip line with almost the same performances. Their impedance bandwidths for $ S_11leq -10~ dB$ are enhanced largely to more than 158%. The radiation patterns are given at 2, 6, and 10 GHz.

A MIMO System With Multifunctional Reconfigurable Antennas

Abstract: A multiple-input-multiple-output (MIMO) system equipped with a new class of antenna arrays, henceforth referred to as multifunction reconfigurable antenna arrays (MRAAs), is investigated. The elements of MRAA, i.e., multifunction reconfigurable antennas (MRAs) presented in this work are capable of dynamically changing the sense of polarization of the radiated field thereby providing two reconfigurable modes of operation, i.e., polarization diversity and space diversity. The transmission signaling scheme can also be switched between transmit diversity (TD) and spatial multiplexing (SM). The results show that the reconfigurable modes of operation of an MRAA used in conjunction with adaptive space-time modulation techniques provide additional degrees of freedom to the current adaptive MIMO systems, resulting in more robust system in terms of quality, capacity and reliability. A performance gain up to 30 dB is possible with the proposed system over conventional fixed antenna MIMO systems depending on the channel conditions

Improved Design Guidelines for the Ultra Wideband Monopole-Dielectric Resonator Antenna

Abstract: This letter examines in detail multiple resonance phenomenon responsible for the ultra wideband response of the hybrid monopole-dielectric resonator antenna (DRA). The physical insight gained by this investigation has lead to improved guidelines for designing the antennas for any specified frequency band. These simple guidelines are then verified using both simulated and measured data

The Role of Polarization Diversity for MIMO Systems Under Rayleigh-Fading Environments

Abstract: Polarization diversity techniques have not received as much attention as others due to the significant difference in mean signal level between copolarized and cross-polarized branches when one polarization is transmitted. However, multiple-input-multiple-output (MIMO) systems where the multipath fading is only partially correlated could use polarization diversity to provide a high diversity gain. Hence there is a need to fully understand the role of true polarization diversity in such systems. In this letter, progressive (true) polarization diversity performance for 3 times 3 MIMO systems under Rayleigh-fading environments is evaluated through simulations and measurements. True polarization diversity was found to be as significant as spatial diversity at improving diversity gain, and hence MIMO system capacity

Concentric Ring-Shaped Defected Ground Structures for Microstrip Applications

Abstract: A new defected ground structure (DGS) consisting of concentric circular rings in different configurations is experimentally studied to examine the stopband characteristics. Unlike previous DGS designs, a metallic shielding is introduced at the back of the DGS to suppress any leakage or radiation, and this would be advantageous for microwave circuit applications. A wide stopband is demonstrated with a set of prototypes designed for X-band. Its application to suppressing mutual coupling in microstrip patch arrays is demonstrated

A Novel Small-Size Printed Tapered Monopole Antenna for UWB WBAN

Abstract: In this letter, a novel antenna topology based on the printed tapered monopole antenna (PTMA) is investigated in view of ultra-wideband (UWB) wireless body area network (WBAN) applications. First, the bandwidth in the presence of a human arm is studied. Second, the pulse distortion of a modulated Gaussian pulse is investigated, based on measured S21-parameters. We observe that there is a small acceptable influence on the matching of the antenna and that the pulse distortion is low. The main conclusion is that this modified PTMA is a very good candidate for WBAN UWB applications

An investigation of stacked and embedded cylindrical dielectric resonator antennas

Abstract: Various multisegment cylindrical dielectric resonator antenna geometries are considered including stacked, core-plugged, and embedded stacked. Results show impedance bandwidths up to 68.1% compared to 21.0% for a homogeneous DRA with the same size and resonant frequency.

Particle Swarm Optimization for the Design of Frequency Selective Surfaces

Abstract: The particle swarm optimization (PSO) is a stochastic strategy that has recently found application to electromagnetic optimization problems. It is based on the behavior of insect swarms and exploits the solution space by taking into account the experience of the single particle as well as that of the entire swarm. This combined and synergic use of information yields a promising tool for solving design problems that require the optimization of a relatively large number of parameters. In this letter, the problem of synthesizing frequency selective surfaces (FSSs) is addressed by using a specifically derived particle swarm optimization procedure, which is able to handle, simultaneously, both real and binary parameters. Representative numerical examples are presented to demonstrate the effectiveness of the method. Finally, the performance of the PSO is compared with that of the genetic algorithm

Design of a Closely Spaced, Folded Yagi Antenna

Abstract: A closely spaced, folded Yagi antenna design is proposed for achieving high gain in a physically compact size. It is shown that a three-element Yagi can achieve a realized gain of more than 6.7 dB, despite the fact that the spacing between the elements is only 0.02lambda. The simulation results are verified by measurements using a monopole version of the design at 1 GHz. The antenna design is then evaluated at 8 MHz over a lossy ground for potential applications in HF skywave transmission

PSO-Based Real-Time Control of Planar Uniform Circular Arrays

Abstract: This letter is aimed at assessing the effectiveness of the phase-only control strategy based on a customized PSO when applied to planar uniform circular arrays (PUCA) and in the presence of interferences both in the near-field and far-field of the antenna. The employed geometry seems to be suitable for a reliable and effective implementation of adaptive arrays in mobile devices thanks to its symmetry and geometric simplicity. For validation purposes, the proposed architecture is evaluated in the presence of a complex time-varying scenario both in terms of synthesized beam patterns and signal-to-interference-plus-noise ratio

A Novel Differential-Fed Patch Antenna

Abstract: A novel differential-fed patch antenna (DFPA) is proposed in this letter. The proposed DFPA can be conveniently integrated with microwave differential circuits. Based on this differential feeding structure, wide bandwidth and good radiation patterns can be obtained. As a demonstration, a DFPA is designed and measured. Experiments show that the proposed DFPA can obtain good patterns with symmetric copolarization and low cross-polarization across a bandwidth of 34.5%

A Double-Sided Rounded Bow-Tie Antenna (DSRBA) for UWB Communication

Abstract: A double-sided rounded bow-tie antenna (DSRBA) for ultrawideband (UWB) communication is proposed. The antenna covers the UWB spectrum from 3.1 to 10.6 GHz, and has return loss below -10 dB throughout the entire band. The antenna has also omnidirectional radiation characteristics and reasonable gain values over the same frequency band. Two different substrates, Rogers RO3006 and Liquid Crystal Polymer (LCP), are considered. Both materials have very low loss tangent. Results regarding return loss, far-field pattern, and gain are presented

Operability of Folded Microstrip Patch-Type Tag Antenna in the UHF RFID Bands Within 865-928 MHz

Abstract: The emerging use of passive radio frequency identification (RFID) systems at ultra-high-frequency (UHF) spectrum requires application specific tag antenna designs for challenging applications. Many objects containing conductive material need novel tag antenna designs for reliable identification. The operability of folded microstrip patch-type tag antenna for objects containing conductive material is analyzed and tested within the UHF RFID bands used at the moment mainly in Europe and in North and South America. First the operability of the tag antenna design and the effects of conductive material are modeled with simulations based on finite element method (FEM). The performance of the tag antenna design affixed to a package containing metallic foil is verified with read range measurements. The results show that the antenna design is operable in both of the UHF RFID bands within 865-928 MHz

Uniplanar Log-Periodic Slot Antenna Fed by a CPW for UWB Applications

Abstract: A coplanar waveguide-fed uniplanar log-periodic slot antenna suitable for use in the ultra-wideband radio systems is presented. The in-band impedances and radiation performances are quite stable and satisfactory. A rejected narrow frequency band is further obtained within the wide bandwidth by inserting a pair of metallic stubs into two vertical slots of the proposed antenna. Experimental results reveal that the stub pair provides significant attenuation in the desired notched band but has little effect on the antenna operation outside of the notch. By means of a normalized antenna transfer function, the time-domain characteristics of the proposed antennas are also investigated. The transient responses show that the designs with and without the notched band are both acceptable for the pulsed systems

A Novel GPS Patch Antenna on a Fractal Hi-Impedance Surface Substrate

Abstract: A compact high-performance circularly-polarized microstrip antenna for the global positioning system application is proposed. It comprises a fractal hi-impedance surface electromagnetic bandgap (EBG) structure printed on a high permittivity substrate. Measurements and simulation of return loss and axial ratio are in good agreement. It is shown that the proposed Global Positioning System antenna has good axial ratio performance in the upper half-plane, an improvement in gain and a significantly wider axial ratio bandwidth when compared to the same antenna without EBG

An Annual Ring Antenna for UWB Communications

Abstract: An ultrawideband (UWB) annual ring antenna is presented in this letter. The annual ring antenna has a return loss better than 10 dB from 2.8 to 12.3 GHz. It has an average gain of 2.93 dBi and has a maximum gain of 5 dBi at 7 GHz. The antenna radiation patterns are stable within its operation band. The parameters determining the antenna wideband characteristic are discussed and measured results are presented

Optimization of the Directivity of a Monopulse Antenna With a Subarray Weighting by a Hybrid Differential Evolution Method

Abstract: The optimization of the directivity of the difference patterns in monopulse array antennas is considered. A subarray configuration is used in order to avoid the need for the implementation of two separate feed networks. An hybrid differential evolution method is applied to contemporarily determinates the weights of the subarrays and the group membership of the elements. Some numerical results are provided together with a validation comparison with data previously published in the literature.

Enhancing the gain of helical antennas by shaping the ground conductor

Abstract: We have observed that the size and shape of the ground conductor of axial mode helical antennas have significant impact on the antenna gain. By shaping the ground conductor, we have increased the gain of a helical antenna for as much as 4 dB. Theoretical results are verified by measurements.

Wideband Cylindrical and Rectangular Dielectric Resonator Antennas

Abstract: An investigation is conducted on increasing the bandwidth of dielectric resonator antennas by changing the radius-to-height and length-to-height ratios for cylindrical and rectangular geometries, respectively. A bandwidth of 30% is experimentally verified

Design of Phase-Differentiated Reconfigurable Array Antennas With Minimum Dynamic Range Ratio

Abstract: In this letter, we propose a real-coded genetic algorithm (GA) for optimal design of reconfigurable dual-beam linear array antennas with phase only control. The problem is to find a common amplitude distribution with minimum dynamic range ratio (DRR) that will generate a pencil beam with zero phases and a flat-top beam with continuously controllable phases of an analog phase shifter. Results are also shown for the same design without minimizing dynamic range ratio (amax /amin) of excitation amplitude

An Inexact Newton Method for Microwave Reconstruction of Strong Scatterers

Abstract: An approach to solve the inverse scattering problem for imaging applications is presented. The proposed algorithm is based on an inexact Newton method applied to the Lippmann?Schwinger integral equation. Inhomogeneous dielectric scatterers with high contrast in a tomographic arrangement are considered. The capabilities of the approach are assessed with reference to several different unknown objects. In particular, both noisy synthetic data and experimental data have been used. Furthermore, a comparison with a model based on the second order Born approximation is also reported.

The design of miniature three-element stochastic Yagi-Uda arrays using particle swarm optimization

Abstract: A fixed grid structure of reduced length is employed to generate three-element miniature stochastic Yagi-Uda arrays. Particle swarm optimization (PSO) is utilized to alter the shape and the element distances for optimum forward gain, good front-to-back ratio, and 2:1 or better voltage standing wave ratio (VSWR). Simulation results of PSO are compared with binary valued genetic algorithm (GA) optimized designs and with a conventional three-element Yagi-Uda array.

Some Insight Over New Variations of the Particle Swarm Optimization Method

Abstract: The Particle Swarm Optimization (PSO) method recently gained high popularity in electromagnetics. Here few variations over the standard algorithm, referred to as Meta PSO, are proposed and the results of their application to the optimization of a microwave microstrip-line filter are presented.