bluuebunny/crossref_metadata_2025 huggingface dataset:
Transcranial imaging of substantia nigra hyperechogenicity in a Taiwanese cohort of Parkinson's disease
Authors: Huang Yu‐Wen , Jeng Jiann‐Shing , Tsai Chung‐Fen , Chen Li‐Ling , Wu Ruey‐Meei
Published: January 2007

Transcranial Doppler imaging (TCDI) has been used as a noninvasive diagnostic tool to differentiate Parkinson's disease (PD) from atypical parkinsonism by detecting hyperechogenicity in the substantia nigra (SN). To our knowledge, no TCDI data are available for Asian populations, and TCDI sensitivity is uncertain across populations. Early‐onset PD (EOPD) represents a specific PD subtype based on clinical features and pathogenic mechanisms. It is not known if EOPD patients have abnormal echogenicity in SN comparable to late‐onset PD (LOPD) patients. We assessed the area of SN hyperechogenicity (hyper‐SN) and a ratio of hyper‐SN over ipsilateral midbrain (S/M ratio) with TCDI in 164 healthy Taiwanese, 40 EOPD patients, and 40 LOPD patients. The upper 95th percentile values for hyper‐SN and S/M ratio were 0.20 cm2 and 0.07. Our results indicate that S/M ratio is a more sensitive measure than hyper‐SN in diagnosing PD. Approximately 92.5% of the LOPD patients and 57.5% of the EOPD patients had S/M ratios ≥ 0.07. Enlarged hyperechogenicity of SN is a common finding in LOPD, but not in EOPD. Iron‐independent mechanisms of SN cell degeneration in EOPD distinct from that in LOPD might contribute to the sonographic findings. © 2007 Movement Disorder Society
Design and implementation of a miniaturized high‐linearity 3–5 GHz ultrawideband CMOS low‐noise amplifier
Authors: Lin Yo‐Sheng , Yang Zheng‐Hua , Chen Chi‐Chen , Chao Tai‐Cheng
Published: January 2007

In this article, we demonstrate a miniaturized high‐linearity (IIP3 = 8 dBm at 4 GHz) 3–5‐GHz ultrawideband low‐noise amplifier (LNA) implemented in a standard 0.18‐μm CMOS technology. The inductive‐series peaking technique was used to enhance the gain and bandwidth performances of the LNA. The measurement results show voltage gain greater than 10 dB, reverse isolation (S12) lower than −15 dB, and noise figure lower than 3.3 dB were achieved for frequencies lower than 5 GHz. In addition, input return loss (S11) lower than −8 dB was achieved for frequencies lower than 4.5 GHz. The chip area is only 0.4 mm2, excluding the test pads. This LNA drains 8.75 mA current at supply voltage of 2 V, i.e., it only consumes 17.5 mW power. These results are helpful for RFIC designers to realize miniaturized high‐linearity RF receiver front‐end ICs. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 524–526, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22175
Analytical study on uneven heating relaxation of food inside industrial microwave oven by means of water film
Authors: Suga Ryosuke , Ijuin Taichi , Hashimoto Osamu , Takatomi Tetsuya , Watanabe Shinya
Published: January 2007

When foods are sterilized by heating in the industrial microwave oven, uneven heating takes place inside the heated foods. This causes inadequate sterilization and deterioration of foods. In this paper, we analyzed temperature distribution of a food inside the industrial microwave oven. Parallel finite‐difference time‐domain method and heat transfer equation are applied to the temperature analysis. As a result, the trend of the temperature distribution inside the food is explained. And, it is confirmed that temperature rise at the edge of the cup is reduced by arranging water film around the food. Basic data for uniform heating of foods is provided. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 518–521, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22177
Rate‐equation‐based circuit model of high‐speed semiconductor lasers
Authors: Zhang S. J. , Zhu N. H. , Pun E. Y. B. , Chung P. S.
Published: January 2007

Based on rate equations of semiconductor laser, a symbolically‐defined model for optical transmission system performance evaluation and network characterization in both time‐ and frequency‐domains is presented. The steady‐state and small‐signal characteristics, such as current–photon density curve, current–voltage curve, and input impedance, can be predicted from this model. Two important dynamic characteristics, second‐order harmonic distortion and two‐tone third‐order intermodulation products, are evaluated under different driving conditions. Experiments show that the simulated results agree well with the published data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 539–542, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22180
Band‐stop filter based on a substrate embedded with metamaterials
Authors: Kong Soon‐Cheol , Thomas Zachary M. , Chen Xudong , Wu Bae‐Ian , Grzegorczyk Tomasz M. , Kong Jin Au
Published: January 2007

The effects of embedding SRR into a substrate of microstrip line are investigated, in particular in transmission. The simulation and experimental results show band‐stop property of the device. Also, reduced radiation loss and device volume are achieved by applying the image theory from a symmetric SRR. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 530–534, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22184
PEC condition implementation for the ADI‐FDTD method
Authors: Chen Juan , Wang Jianguo
Published: January 2007

The perfect‐electric‐conductor (PEC) condition implementation for the alternating‐direction‐implicit finite‐difference time‐domain (ADI‐FDTD) method is discussed in this article. By comparing different implementation strategies, it shows that the most accurate implementation method is that the PEC condition is directly incorporated within the tridiagonal matrix. Compared with the other two methods commonly used in conventional FDTD, this method is unconditionally stable and has higher accuracy. The theory proposed in this article is validated through numerical examples. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 526–530, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22185
Simple estimation formulas for rectangular dielectric waveguide single‐mode range and propagation constant
Authors: Hamilton Dean P. , Green Roger J. , Leeson Mark S.
Published: January 2007

Closed‐form formulas for estimating the single‐mode frequency range and propagation constant of open rectangular dielectric waveguides are presented. The formulas are based on curve fitting to normalized results by the popular Marcatili method, suitably modified to reduce error. Excellent agreement with independent experimental data is reported. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 503–505, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22187
Planar slot antenna with PBG filter for wireless communications
Authors: Consoli Fabrizio , Catalano Rocco , Laudani Roberto , Tumino Livia , Barbarino Sebastiano
Published: January 2007

A planar circular slot antenna, integrated with a band‐stop photonic bandgap filter is presented here. The complete realized prototype is suitable to cover the bandwidth requirements of many wireless communication standards in one solution. The work describes the detailed study of both the antenna and the PBG filter properties. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 551–555, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22191
Simultaneously all‐optical inverted and noninverted wavelength conversion employing SOA‐based Sagnac interferometer
Authors: Chen Zhixin , Wu Jian , Xu Kun , Lin Jintong
Published: January 2007

This paper have successfully demonstrated an all‐optical wavelength conversion scheme for all‐speed return‐to‐zero (RZ) format data at 10 Gbit/s rate by using a Sagnac interferometer based on semiconductor optical amplifier (SOA). The attractive issue of the proposed method is that the converted signal can be obtained simultaneously with inverted and noninverted wavelength conversion signals. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 547–551, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22192
A wide rejection bandwidth bandpass filter with stepped‐impedance hairpin resonator and interlaced coupled‐line
Authors: Her Man‐Long , Hsu Ming‐Wei , Wu Ying‐De , Ko Wen , Hsu Chou‐Jung
Published: January 2007

In this paper, a wide rejection bandwidth bandpass filter with stepped‐impedance hairpin (SIH) resonator and interlaced coupled‐line was proposed. With the former, its elliptic‐function low‐pass response was adopted to steepen the upper roll off characteristic and flatten the rejection level; the latter was utilized to broaden the rejection bandwidth by shifting the transmission zero. Measured results show that the filter with interlaced length λ2 mm has suppressed the second harmonic response from −19 to −53 dB when compared to three stages conventional parallel coupled‐line filter. Moreover, the upper rejection bandwidth was expanded from 3.2 to 4.5 GHz when the interlaced coupled‐line was increased from 0 to 3 mm, which stands for 40% improvement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 542–545, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22194
Application of effective index method to higher order modes of photonic crystal fibers
Authors: Li Yanfeng , Wang Ching‐yue , Peng Yan , Hu Minglie , Chen Yongyao , Liu Bowen , Chai Lu
Published: January 2007

The application of effective index method (EIM) to calculate the modal indices of higher order modes (HOMs) of photonic crystal fibers (PCFs) is investigated. The effective index of the fiber cladding is obtained by a plane wave expansion method because analytical solution is found to induce large errors for PCFs with large air holes. The modal indices of the TE01 and TM01 modes of a PCF are solved using EIM as a demonstration of the applicability of this method. It is shown that there exists a different optimized core for these two modes when compared with the case for the fundamental HE11 mode. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 567–570, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22196
Assessment of design procedures of nearly axis‐symmetric shaped lens antennas: A comparative study between 2‐D and 3‐D formulations
Authors: Sauleau Ronan , Barès Barbara
Published: January 2007

Shaped integrated lens antennas (ILAs) are attractive for beam‐shaping applications at millimeter waves and specific synthesis methodologies have been proposed for their design. The purpose of this paper is two‐fold. First, we focus on the particularities associated with the geometrical optics/physical optics (GO/PO) analysis of numerically‐specified arbitrarily‐shaped ILAs, namely (i) the interpolation procedures of generic 3‐D ILAs and (ii) the computation of their surface curvature parameters. In particular, new closed‐form expressions of the principal radii of curvature of a curved interface are established. Second, two synthesis procedures, previously implemented for nearly axis‐symmetric and arbitrarily‐shaped ILAs, are compared and discussed numerically and experimentally. To this end, two ILAs made from Teflon are designed and fabricated, starting from the same radiation specification at 58.5 GHz (the amplitude template is a circularly‐symmetric pencil beam). Both prototypes are fed by a 2 × 2 elements microstrip antenna array. The experimental results are in satisfactory agreement with the simulations. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 615–622, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22198
A 4 × 4 Butler matrix optimized for UMTS applications
Authors: Kaifas Theodoros N. , Sahalos John N.
Published: January 2007

A 4 × 4 Butler matrix (BM) optimized for UMTS applications is presented. Special care is taken for the design of the elliptic couplers and the line crossovers. The BM is fabricated by conventional photolithography on a single laminate. No expensive double layer/multilayer or high permittivity substrates or high‐temperature superconductors are used. The design is compact and complies with the bandwidth specifications of the UMTS band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 585–588, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22200
Compact bandpass filter using modified CMRC and double‐sided parallel‐strip line
Authors: Zhang Xiu‐Yin , Xue Quan , Hu Bin‐Jie
Published: January 2007

A novel bandpass filter using modified compact microstrip resonant cell (CMRC) and double‐sided parallel‐strip line is proposed in this article. On the basis of the modified CMRC resonator, the proposed filter has compact size. Moreover, this filter obtains a low insertion loss and sharp rejection. A demonstration filter was designed, fabricated and measured. Theoretical and experimental results are presented and show good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 583–585, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22201
Improvement of the resonant characteristics of the short‐ended stub by the optimal arrangement positions of via‐holes
Authors: Wu Ifong , Nishizawa Shinichiro , Hashimoto Osamu
Published: January 2007

A method for improving the resonant characteristic of the short‐ended stub is proposed by locating the via‐holes on the optimal position on the ground. In the first step, the optimal length of the stub at 1 GHz is evaluated by comparing the numerical calculated result and the measured result (used the fabricated stub), which is based on the theoretical calculation, and the resonant characteristics shifted to the lower frequency regions. These shifting phenomena of the resonant characteristics are caused by the via‐hole. When the via‐hole is arranged on the substrate, the via‐hole becomes part of the stub, and the length of the stub becomes longer than the theoretical calculation. As a result, a good agreement between both results is achieved when the stub length is 27.43 mm, and hence the optimal length of the stub is confirmed. For the second step, the optimal arrangement position of the via‐holes is evaluated by using current distribution on the stub model. In this study, we applied the Green's function method to obtain the current distribution. The improvement of resonant characteristic is achieved by arranging the via‐holes on the place where the currents concentrate. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 642–645, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22202
Sensitivity analysis of iterative adjoint technique for microstrip circuits optimization
Authors: Yuan Tao , Qiu Cheng‐Wei , Li Le‐Wei , Zouhdi Saïd , Leong Mook‐Seng
Published: January 2007

This paper presents an accurate and efficient full‐wave method, combined with iterative adjoint technique, for analyzing sensitivities of planar microwave circuits with respect to design parameters. Method of moments (MoM) in spatial domain is utilized, and generalized conjugate residual iterative scheme is applied to solve the linear matrix equations with fast convergence. Green's functions for multilayer planar structures in DCIM form are employed to simplify the spatial domain manipulation. In the present method, a conventional integration model and the corresponding adjoint model are solved by MoM respectively. The adjoint technique, with the aid of iterative schemes, could significantly reduce the computational requirements, especially for the large electrical size device with many perturbing design parameters. Numerical results of S‐parameter sensitivities of a low‐pass microstrip filter by the present method are presented. Accuracy and efficiency are validated. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 607–609, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22204
A planar‐type dielectric resonator and filter using LTCC process
Authors: Yim Jounghyun , Kang Daehyun , Son Seokho , Kim Bumman
Published: January 2007

A new structure planar‐type dielectric resonator (PDR) with high Q has been developed using an LTCC process. The PDR consists of two different dielectric constant materials, a hollow patch center ground plane in the middle of the cavity layer and shielded cavity metals. The realized PDR shows a high unloaded‐Q factor of about 1920 at 34.3 GHz. We also developed a dual mode band‐pass filter using the proposed PDR, demonstrating a compact filter at a millimeter‐wave band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 578–581, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22206
Omnidirectional circularly polarized slot antenna fed by a cylindrical waveguide in millimeter band
Authors: Masa‐Campos José Luis , Fernández J. M. , Sierra‐Pérez M. , Fernández‐Jambrina José Luis
Published: January 2007

A circularly polarized slotted array antenna is presented. The array is fed by a circular waveguide propagating the TM01, to properly generate the required polarization. An omnidirectional azimuth radiation pattern is obtained, as well as a −10°/+30° elevation antenna coverage. Low losses are achieved because of the waveguide feed. The slot array is mechanized over the metallic wall of the circular waveguide. Furthermore, the antenna presents a solid and rigid mechanical structure, which guarantees an optimum and repetitive response in a manufacturing process. A prototype antenna has been designed and measured. Satisfactory results have been obtained. The slotted array takes part from a signal detection system centered in 36.85 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 638–642, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22207
Reliability of loss‐coupled 1.55 μm DFB laser diode with automatically buried absorptive InAsP layer
Authors: Han Jae‐Ho , Park Sung‐Woong
Published: January 2007

The authors achieved loss‐coupled 1.55 μm distributed feedback laser diode incorporating automatically buried absorptive layer implemented by a single step growth that simplifies device fabrication than those of conventional ones. Based on 2800 h of accelerated aging test, estimated lifetime is 1.4 × 106 h at room temperature. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 636–638, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22208
Circularly polarized microstrip antenna using asymmetric ring‐sector slots embedded on the ground plane
Authors: Baik Jungwoo , Kim Sangjoong , Kim Youngsik
Published: January 2007

A single‐feed circularly polarized (CP) microstrip antenna using asymmetric ring‐sector two‐pair slots embedded on the ground plane is proposed. Asymmetric ring‐sector two‐pair slots on the ground plane can easily increase the antenna gain 2.8 dBi (5.0 dBi versus 2.2 dBi) higher than that of the same substrate material, operating frequency, and radiating patch shape of a conventional microstrip with slotted ring segment on the patch. Antenna gain and CP performance can be adjusted the ring‐sector slot size. Details of the antenna design are described, and obtained performances are presented and analyzed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 602–604, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22210
A very compact 62‐GHz transmitter LTCC SiP module for wireless terminals applications
Authors: Lee Young Chul , Park Chul Soon
Published: January 2007

A 10 × 21 × 1 mm3, very compact low temperature cofired ceramic (LTCC) system‐in‐package (SiP) transmitter module is presented for future wireless terminal applications. Five GaAs monolithic microwave integrated circuits (MMIC) chipsets including a power amplifier, driver amplifier, mixer, and two frequency multipliers are integrated into a LTCC multilayer circuit for the heterodyne transmitter. The fabricated transmitter module achieves an output of 13 dBm at a RF frequency of 62 GHz, an IF frequency of 2.4 GHz, and an local oscillator frequency of 59.6 GHz. The up‐conversion gain is 11 dB; while the local oscillator signal is suppressed below −20.6 dBc with the image rejection mixer, and the image and spurious signals are also suppressed below −29.6 dBc. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 575–578, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22211
Back‐propagation based nonbinary optical code for OCDMA with fiber gratings
Authors: Min Seong‐Sik
Published: January 2007

A new optical code is proposed for OCDMA networks with optical gratings and balanced detection, in which the back‐propagation algorithm of a neural network is applied to nonbinary optical code generation. The proposed codes have high security level and a code ratio of at least 1.0. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 632–636, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22213
Wide band planar modified triangular monopole antennas
Authors: Ray K. P. , Kumar G. , Anob P. V.
Published: January 2007

Various new configurations of planar triangular monopole antennas have been investigated. Effect of flaring angle of planar triangular monopole antennas on the bandwidth has been studied. A compact configuration of vertex chopped equilateral triangular monopole antenna has been proposed for ultra wide bandwidth ratio of 9.2:1. Orthogonal vertex chopped equilateral triangular monopole antenna is proposed for obtaining the improved azimuthal omnidirectional radiation pattern. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 628–632, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22214
Numerical analysis of large reflector system used as a ground station antenna
Authors: Farahat Nader , Mittra Raj , Carrión José , Sanchez Jesus
Published: January 2007

In this paper we investigate a large dual‐reflector (Cassegrain) antenna system, typically used as a ground station antenna in the space communication link. The study includes the blockage effects of the subreflector and the struts on the radiation performance of the antenna, as well as the estimation of the combination to the pattern degradation due to the panel gaps. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 597–602, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22215
Broad‐band power divider based on radial waveguide
Authors: Song Kaijun , Fan Yong , Zhang Yonghong
Published: January 2007

A broad‐band power divider using coaxial probes and a radial waveguide is presented. The simple modeling of this power divider and design method based on equivalent circuits has been developed. A four‐way radial waveguide power divider has been designed, fabricated, and measured. Close agreement is obtained between the measured results and the simulated results. The measured 15‐dB return loss bandwidth of the broad‐band multiple‐port structure is demonstrated to be 81.5% and its 0.5‐dB insertion loss bandwidth 84.6%. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 595–597, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22216
Stopband‐improved dual‐mode bandpass filter using side‐slit patch resonator
Authors: Li Rui , Zhu Lei
Published: January 2007

A rectangular patch resonator with four equal slits etched on sides is presented to make up a stopband‐improved dual‐mode filter. By stretching these four side slits towards the patch center, the first resonant frequency gets a gradual decrease while its second one keeps almost unchanged. This feature is attractive in widening upper stopband while miniaturizing overall size in filter design. To realize a relatively wide passband with DC‐blocking, the narrowed feed lines are deeply inserted into their respective slits, resulting in the enhanced capacitive coupling degree. Our studies imply that the spacing between the first two resonant frequencies of this resonator itself is increased by about 50% while the first spurious resonant frequency is fully rejected by introducing a pair of open‐circuited stubs in the feed lines. In final, a dual‐mode filter is optimally designed with a fractional bandwidth of 4.5% at 1.60 GHz and predicted results are confirmed by experiment. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 717–720, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22221
Experimental characterization of a broadband dual‐polarized microstrip antenna for X‐band SAR applications
Authors: Wang Wei , Liang Xian‐Ling , Zhang Yu‐Mei , Zhong Shun‐Shi , Guo Yan
Published: January 2007

The design and development of a broadband dual‐polarized 16 × 16 element microstrip antenna array for X‐band application is introduced. The measured bandwidth is about 17.8% for voltage standing wave ratios <1.5. The polarization isolation is better than 45 dB. The cross‐polarization component is at the level of −37 dB below the main lobe. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 649–652, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22225
Accurate computation of the impedance elements of the magnetic‐field integral equation with RWG basis functions through field‐domain and source‐domain integral swapping
Authors: Ubeda Eduard , Heldring Alex , Rius Juan M.
Published: January 2007

We present a new strategy to compute the impedance elements of the Magnetic‐Field Integral Equation (MFIE) formulation in Method of Moments (MoM) with a discretization of low‐order divergence‐conforming basis functions (RWG). The impedance matrix elements are accurately computed by swapping the inner‐ and outer‐integrals in the accurate computation of a MoM–MFIE discretization with low‐order curl‐conforming basis functions (nxRWG). © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 709–712, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22228
A hyperbolic summation method to focus B‐scan ground penetrating radar images: An experimental study with a stepped frequency system
Authors: Ozdemir Caner , Demirci Sevket , Yigit Enes , Kavak Adnan
Published: January 2007

There are many techniques to focus raw B‐scan ground penetrating radar (GPR) images mainly distorted from well‐known hyperbolic dispersion. In this study, we apply a hyperbolic summation (HS)‐type focusing technique to the simulated and measured GPR data at C‐band frequencies. The formulation of the proposed HS method is presented. Numerical GPR images for different metal targets are generated by the help of a physical optics simulation code. An experimental set‐up is constructed with the help of a stepped frequency radar system and corresponding B‐scan images are generated. Proposed HS method is applied to the measured B‐scan GPR data. Focused GPR images of different objects were obtained for both the simulated and the experimental data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 671–676, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22230
Dual‐band circularly polarized antenna with a QUAD‐EMC structure
Authors: Chang The‐Nan , Ni Guo‐Yang
Published: January 2007

In this paper, a method for obtaining a single‐feed dual‐band circularly polarized (CP) antenna with QUAD‐EMC structure is presented. The proposed dual‐band CP design was achieved by four small patches displayed on the upper surface of a first substrate, and fed electromagnetically by a large patch etched on the lower surface of the same substrate. A second FR4 and a third air substrate were added behind the first substrate to enhance the gain of the antenna. Then, by tuning the sizes of upper and lower patches and truncating patch corners respectively and properly, the proposed antenna can perform dual‐band CP radiation using a single probe feed. Prototypes of the proposed antennas designed for RFID operations in the 915‐MHz and 2.45‐GHz bands are presented and experimentally demonstrated. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 645–647, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22231
Hybrid mode matching and auxiliary sources technique for horn antenna analysis
Authors: Diamantis S. G. , Orfanidis A. P. , Kyriacou G. A. , Sahalos J. N.
Published: January 2007

A hybrid technique for the analysis of horn antennas is described based on a rigorous description of the horn aperture‐free space discontinuity. The transition from the feeding waveguide to the radiating aperture is analyzed by using the mode matching technique (MMT) employing a stepped‐waveguide approach. The discontinuity between the horn aperture and the free space is modeled by combining the method of auxiliary sources with the MMT for the stepped waveguide section. Results for the input standing wave ratio are given and compared with the available measurements, which demonstrate the very good performance of the method. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 734–739, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22233
A jumping genes paradigm for the design of wide‐band patch antenna with double shorting wall
Authors: Yeung S. H. , Luk W. T. , Ng H. K. , Man K. F. , Chan C. H.
Published: January 2007

A newly developed evolutionary computing algorithm, Jumping Genes Evolutionary Algorithm is applied to optimize the dimensions of a folded patch antenna with double shorting walls. In the optimized design, an impedance bandwidth (VSWR ≤2) of 101% is recorded, which shows an improvement by 29% comparing with its original design. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 706–709, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22234
Circularly polarized omnidirectional millimeter wave monopole with parasitic strip elements
Authors: Fernández J. M. , Masa‐Campos J. L. , Sierra‐Pérez M.
Published: January 2007

A circularly polarized omnidirectional millimeter wave monopole with parasitic strip elements for a system of arrival signal direction detection in millimeter band is presented. As a consequence of the radiation pattern requirements, the proposed antenna consists of a conical skirt monopole with a polarizer radome. The polarizer converts a wave from linear to circular polarization. The proposed antenna has the advantage to be robust, low cost, and easy to fabricate with conventional materials and printed circuit technology. The study presents simulation and experimental results obtained with an antenna prototype that validate the design. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 664–668, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22237
A novel miniaturized triband PIFA for MIMO applications
Authors: Manteghi Majid , Rahmat‐Samii Yahya
Published: January 2007

Multiband antennas are vital in meeting the modern telecommunication demands of mobile terminals. Using the spatial properties of multipath channels, multiple‐input multiple‐output (MIMO) communication systems employ antenna arrays to increase their communication capacity. This article presents a novel printed inverted “F” antenna (PIFA), which has been used to design a miniaturized triband antenna. In turn, the triband antenna has been used as an element in various arrays of MIMO applications. Specifically, the antenna element has been constructed and applied, in arrays of two and four, in a laptop PCMCIA wireless LAN card. The size of the four element MIMO antenna array is 50 mm × 13 mm × 8 mm, which translates to 0.4λ × 0.1λ × 0.06λ at 2.45 GHz. The input impedance of the single element antenna has been measured at UCLA. The antenna has a return loss lower than −10 dB within the 2.4–2.5 GHz, 5.15–5.35 GHz, and 5.7–5.85 GHz bands. The measured scattering matrices of two and four element arrays have been used to calculate the total active reflection coefficient (TARC). TARC has been calculated for different combinations of excitation signals applied at each port. Each excitation signal has a unity magnitude and a random phase, thus leading to innumerable signal combinations. Our results reveal that “off” diagonal elements of the scattering matrix (couplings between elements) are as important as diagonal elements in calculating the TARC and the radiation efficiency of arrays. Furthermore, increasing the number of elements in a MIMO system with a limited volume will increase the channel capacity but lower the radiation efficiency. The experimental and simulation results have been in agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 724–731, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22239
Silicon gap‐loaded microstrip slit‐tetragonal resonator under IR‐irradiation
Authors: Zouganelis G. , Budimir D.
Published: January 2007

A microstrip slit‐tetragonal resonator gap‐loaded with a piece of silicon is proposed as optical tuning element. Change of photoconductivity of silicon, after irradiation of it with an infrared lamp, results a significant change of density (∼25 dB) of the first resonant peak (n = 1/2) of resonator. This behavior makes this device a possible candidate for optical tuning of microwave transmission lines at specific operating frequency. Measured S‐parameters of the proposed device are in good agreement with simulated ones found from finite difference time domain method. Calculation of S‐parameters based on a transmission line model is included for comparison. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 699–702, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22240
Planar monopole antenna with wideband operation
Authors: Tseng Ching‐Fang , Huang Cheng‐Liang
Published: January 2007

A simple printed monopole antenna with wideband operation is presented. The proposed antenna has excellent impedance bandwidth coving the range from 1.926 to 4.9 GHz. The obtained impedance bandwidth reaches ∼123.9% (10‐dB return loss) for 2.4 GHz, which meets the required bandwidth specifications of IEEE 802.11 b/g standards. The simulated return loss shows good agreement with the measured data. Good antenna gain and radiation patterns of the proposed antenna have also been observed across the operating band. Details of the proposed antenna design and experimental results are presented and discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 696–699, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22241
Ultra‐wideband planar elliptical slot antenna with finite‐ground coplanar waveguide‐fed
Authors: Li Jia‐Lin , Qu Shi‐Wei , Xue Quan
Published: January 2007

A planar elliptical slot antenna designed for ultra‐wideband applications is investigated. With elliptical radiation slots and finite‐ground coplanar waveguide feeding structure, the proposed antenna exhibits excellent broadband properties, stable radiation patterns, and compact size. Meanwhile, by introducing a V‐shaped slot on the transition region between the feeding line and the slots, a narrow band‐rejection operation can be realized. Simulated and measured results are presented and discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 662–664, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22242
Linear tunable dispersion compensation device using selective stretching in chirped fiber Bragg grating
Authors: Romero R. , Frazão O.
Published: January 2007

A linear tunable dispersion compensation device based on a chirped grating (CFBG) mounted on a stretching mechanical structure is described. The tunability is obtained changing the CFBG bandwidth without modification of the total length structure. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 720–722, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22245
Correction factor to be applied to the SAR in phantom models for occupational electromagnetic exposure
Authors: Joseph Wout , Vermeeren Günter , Martens Luc
Published: January 2007

A correction factor dependent upon frequency, type of phantom, and incident polarization, which should be applied to the measured specific absorption rate is proposed for homogeneous phantoms. It is shown for an application of occupational exposure in the neighborhood of a base station antenna that this correction factor not underestimates realistic exposure of workers. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 652–655, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22249
Boosting the sampling efficiency ofq‐ball imaging using multiple wavevector fusion
Authors: Khachaturian Mark H. , Wisco Jonathan J. , Tuch David S.
Published: January 2007

q‐Ball imaging (QBI) is a high‐angular‐resolution diffusion imaging (HARDI) method that is capable of resolving complex, subvoxel white matter (WM) architecture. QBI requires time‐intensive sampling of the diffusion signal and large diffusion wavevectors. Here we describe a reconstruction scheme for QBI, termed multiple wavevector fusion (MWF), that substantially boosts the sampling efficiency and signal‐to‐noise ratio (SNR) of QBI. The MWF reconstruction operates by nonlinearly fusing the diffusion signal from separate low and high wavevector acquisitions. The combination of wavevectors provides the benefits of the high SNR of the low wavevector signal and the high angular contrast‐to‐noise ratio (CNR) and peak separation of the high wavevector signal. The MWF procedure provides a framework for combining diffusion tensor imaging (DTI) and QBI. Numerical simulations show that MWF of DTI and QBI provides a more accurate estimate of the diffusion orientation distribution function (ODF) than QBI alone. The accuracy improvement can be translated into an efficiency gain of 274–377%. An intravoxel peak connectivity metric (IPCM) is presented that calculates the peak connectivity between an ODF and its neighboring voxels. In human WM, MWF reveals more detailed WM architecture than QBI as measured by the IPCM for all sampling schemes presented. Magn Reson Med 57:289–296, 2007. © 2007 Wiley‐Liss, Inc.
Restricted field of view magnetic resonance imaging of a dynamic time series
Authors: Pisani Laura , Bammer Roland , Glover Gary
Published: January 2007

A restricted field of view (rFOV) approach for imaging a dynamic time series of volumes of limited spatial extent within a larger subject is described. The shorter readout with rFOV‐MRI can be exploited to either limit image artifacts or increase spatial resolution. To accomplish rFOV imaging of a multislice volume for a dynamic series, an outer volume suppression (OVS) preparation that saturates signal external to a cylinder through the subject is followed by slice‐selective excitation and a spiral readout. The pass‐ and stopband efficiencies of the OVS in an agar gel phantom were 97% (±1.5%) and 3% (±1%), respectively. Profiles of the temporal signal‐to‐noise ratio (SNR) were measured in a phantom and an adult brain. The rFOV sequence reduced distortions from off‐resonance signal and T‐induced blurring compared to a conventional sequence. Sequence utility is demonstrated for high‐resolution rFOV functional MRI (fMRI) in the visual cortex. The rFOV sequence may prove to be useful for other multislice dynamic and high‐resolution imaging applications. Magn Reson Med 57:297–307, 2007. © 2007 Wiley‐Liss, Inc.
Sensitivity‐encoded (SENSE) proton echo‐planar spectroscopic imaging (PEPSI) in the human brain
Authors: Lin Fa‐Hsuan , Tsai Shang‐Yueh , Otazo Ricardo , Caprihan Arvind , Wald Lawrence L. , Belliveau John W. , Posse Stefan
Published: January 2007

Magnetic resonance spectroscopic imaging (MRSI) provides spatially resolved metabolite information that is invaluable for both neuroscience studies and clinical applications. However, lengthy data acquisition times, which are a result of time‐consuming phase encoding, represent a major challenge for MRSI. Fast MRSI pulse sequences that use echo‐planar readout gradients, such as proton echo‐planar spectroscopic imaging (PEPSI), are capable of fast spectral‐spatial encoding and thus enable acceleration of image acquisition times. Combining PEPSI with recent advances in parallel MRI utilizing RF coil arrays can further accelerate MRSI data acquisition. Here we investigate the feasibility of ultrafast spectroscopic imaging at high field (3T and 4T) by combining PEPSI with sensitivity‐encoded (SENSE) MRI using eight‐channel head coil arrays. We show that the acquisition of single‐average SENSE‐PEPSI data at a short TE (15 ms) can be accelerated to 32 s or less, depending on the field strength, to obtain metabolic images of choline (Cho), creatine (Cre), N‐acetyl‐aspartate (NAA), and J‐coupled metabolites (e.g., glutamate (Glu) and inositol (Ino)) with acceptable spectral quality and localization. The experimentally measured reductions in signal‐to‐noise ratio (SNR) and Cramer‐Rao lower bounds (CRLBs) of metabolite resonances were well explained by both the g‐factor and reduced measurement times. Thus, this technology is a promising means of reducing the scan times of 3D acquisitions and time‐resolved 2D measurements. Magn Reson Med 57:249–257, 2007. © 2007 Wiley‐Liss, Inc.
Magnetic field and tissue dependencies of human brain longitudinal 1H2O relaxation in vivo
Authors: Rooney William D. , Johnson Glyn , Li Xin , Cohen Eric R. , Kim Seong‐Gi , Ugurbil Kamil , Springer Charles S.
Published: January 2007

Brain water proton (1H2O) longitudinal relaxation time constants (T1) were obtained from three healthy individuals at magnetic field strengths (B0) of 0.2 Tesla (T), 1.0T, 1.5T, 4.0T, and 7.0T. A 5‐mm midventricular axial slice was sampled using a modified Look‐Locker technique with 1.5 mm in‐plane resolution, and 32 time points post‐adiabatic inversion. The results confirmed that for most brain tissues, T1 values increased by more than a factor of 3 between 0.2T and 7T, and over this range were well fitted by T1 (s) = 0.583(B0)0.382, T1(s) = 0.857(B0)0.376, and T1(s) = 1.35(B0)0.340 for white matter (WM), internal GM, and blood 1H2O, respectively. The ventricular cerebrospinal fluid (CSF) 1H2O T1 value did not change with B0, and its average value (standard deviation (SD)) across subjects and magnetic fields was 4.3 (±0.2) s. The tissue 1/T1 values at each field were well correlated with the macromolecular mass fraction, and to a lesser extent tissue iron content. The field‐dependent increases in 1H2O T1 values more than offset the well‐known decrease in typical MRI contrast reagent (CR) relaxivity, and simulations predict that this leads to lower CR concentration detection thresholds with increased magnetic field. Magn Reson Med 57:308–318, 2007. © 2007 Wiley‐Liss, Inc.
MR lymphangiography using dendrimer‐based contrast agents: A comparison at 1.5T and 3.0T
Authors: Hama Yukihiro , Bernardo Marcelino , Regino Celeste A.S. , Koyama Yoshinori , Brechbiel Martin W. , Krishna Murali C. , Choyke Peter L. , Kobayashi Hisataka
Published: January 2007

Most macromolecular contrast agents (CAs) show lower r1 and higher r2 relaxivities at 3.0T than at 1.5T. MR lymphangiography in mice using a macromolecular G6 dendrimer‐based CA was serially performed and compared at both 1.5T and 3.0T. The r1 and r2 relaxivities of the G6 CA were 25 and 78/s/mM at 1.5T and 17 and 82/s/mM at 3.0T, respectively. The lymph node (LN)‐to‐fat ratios (LN signal intensity (SI)/fat SI) of T1‐weighted 3D‐fast spoiled gradient‐echo (3D‐FSPGR) were 3.2 ± 0.4 (mean ± standard deviation (SD)) at 1.5T and 2.7 ± 0.3 at 3.0T (P = 0.021), and the LN‐to‐fat ratios of T2/T1‐weighted 3D‐fast imaging employing steady‐state acquisition with phase cycling (3D‐FIESTA‐C) were 1.8 ± 0.2 at 1.5T and 1.2 ± 0.4 at 3.0T (P = 0.003). Although 3D‐FSPGR successfully delineated the LNs at both 1.5T and 3.0T, 3D‐FIESTA‐C at 3.0T failed to visualize the LNs. Magn Reson Med 57:431–436, 2007. © 2007 Wiley‐Liss, Inc.
Direct validation of in vivo localized 13C MRS measurements of brain glycogen
Authors: Lei Hongxia , Morgenthaler Florence , Yue Tianwen , Gruetter Rolf
Published: January 2007

With the use of localized 13C MRS in conjunction with [1‐13C]‐D‐glucose infusion, it is possible to study brain glycogen metabolism in vivo. The purpose of this study was to validate in vivo 13C MRS measurements by comparing them with results from a standard biochemical assay. To increase the [1–13C] glycogen concentration, 11 rats were subjected to an episode of acute hypoglycemia followed by a mild hyperglycemic recovery period during which [1‐13C]‐D‐glucose was infused. The total brain [1‐13C] glycogen of the same animal was determined from the enzymatically determined total brain glycogen content, which was fixed by focused microwave irradiation (4 kW in 1.4 s) immediately after the end of the in vivo NMR measurements. The corresponding isotopic enrichment (IE) of glycogen was measured by in vitro 1H MRS of protons bound to glucose C1‐α. The in vivo [1‐13C] glycogen concentration was strongly correlated to the in vitro [1‐13C] glycogen content determined by biochemical measurement in a linear manner (R = 0.79). The results are consistent with the notion that localized 13C MRS measurements closely reflect 13C glycogen content in the brain. Magn Reson Med 57:243–248, 2007. © 2007 Wiley‐Liss, Inc.
Inability to directly detect magnetic field changes associated with neuronal activity
Authors: Parkes Laura M. , de Lange Floris P. , Fries Pascal , Toni Ivan , Norris David G.
Published: January 2007

The ability to directly detect neuronal magnetic fields by MRI would help investigators achieve the “holy grail” of neuroimaging, namely both high spatial and temporal resolution. Both positive and negative findings have been reported in the literature, with no clear consensus as to the feasibility of direct detection. The aim of this study was to replicate one of the most promising published in vivo results. A second aim was to investigate the use of steady‐state visual evoked potentials (ssVEPs), which give a large evoked response and offer a well‐controlled approach because the frequency of the neuronal response can be dictated by the experimenter. For both studies we used a general linear model (GLM) that included regressors for both the expected blood oxygen level‐dependent (BOLD) signal and the magnetic source (MS) signal. The results showed no activity that could be attributed to the neuromagnetic signals in either study, and no frequency component corresponding to the frequency of the ssVEPs. This study demonstrates that for the particular stimuli and hardware used, the sensitivity of the magnitude MRI signal to detect evoked neuronal currents is too low to be of practical use. Magn Reson Med 57:411–416, 2007. © 2007 Wiley‐Liss, Inc.