Symmetrical Feeding Research Articles

Broadband miniaturised bow‐tie antenna for 3D microwave tomography

A broadband, miniaturised bow-tie antenna array element designed to be used in three-dimensional (3D) microwave imaging systems based on the tomographic approach is proposed. Miniaturisation is achieved by adding inductive strips to the capacitive antenna element and thereby lowering the cutoff operational frequency. Furthermore, the broadband directive radiation characteristic of the antenna with the proposed feeding network is equivalent to that of the same antenna being fed by an ideally symmetrical feeding network. This characteristic assists in the modelling of the antenna in the numerical solver. The proposed broadband antenna covering 0.85–3.25 GHz is a compact, directive element with a simple structure having the potential to be implemented in the numerical solver in 3D microwave tomography without imposing a high computational cost on the solver.

Design of a Dual-Band High-Gain Antenna Array for WLAN and WiMAX Base Station

A dual-band $3 \times 2$ antenna array with high gain is presented in this letter. A dual-band folded dipole antenna is utilized as the antenna array element. A broadband symmetric feed network is designed to maintain each array element with the identical current magnitude and phase. The antenna array has a low profile of 12 mm (about $0.1{\lambda _{\rm L}}$ ; ${\lambda _{\rm L}}$ is the wavelength in free space at the lowest operating frequency). Dual bands $2.3\!\sim\! 2.56$ and $3\!\sim\! 4.2~\hbox{GHz}$ for return loss (RL) being higher than 10 dB can be obtained in simulation, while two 10-dB RL bands $2.31\!\sim\! 2.51$ and $3.1\!\sim\! 4.15~\hbox{GHz}$ in measurement cover the wireless local area network (WLAN, $2.4\!\sim\! 2.48~\hbox{GHz}$ ) and Worldwide Interoperability for Microwave Access (WiMAX, $3.3\!\sim\! 3.8~\hbox{GHz}$ ). The measured results also show that this planar antenna array has a high gain $14.3\!\sim \!15.1~\hbox{dBi}\;(2.31\!\sim\! 2.51~\hbox{GHz})$ , $16.2\!\sim\! 17.3~\hbox{dBi}$ ( $3.1\!\sim\! 4.15~\hbox{GHz}$ ) in $ + { z}$ -direction and a low cross-polarization level $ .

The Influence of Symmetrical Feed:Fast Regimes on Oxytetracycline Uptake and Otolith Score in Yellow Perch

Periods of growth from symmetric feed:fast regimes (i.e., days fed followed by the same number of days fasted) may increase the uptake of oxytetracycline (C22H24N2O9 .HCL[OTC]) compounds in fishes; however, little empirical data exists. Therefore, we experimentally determined if such feeding regimes influenced the concentration of OTC incorporated in muscle and skeletal (e.g., otoliths) tissues. Individually-reared female and batch-reared (male and female), age-1 yellow perch Perca flavescens were subjected to one of four experimental feeding regimes: control (i.e., fed daily), D2 (i.e., 2d feed, 2d deprivation), D6, or D12 symmetrical feed:fast regimes. Following several feeding cycles on these feeding regimes, fish were submersed in a 600mg/L buffered OTC solution; otoliths and muscle tissue were excised and processed to determine OTC uptake via mark quality and concentrations. Ranked otolith scores (mark quality) were significantly lower for the D2 feeding regime than control, D6, and D12 scores for both individual and batch trials suggesting that frequent food deprivation restricts osteogenesis, while daily or extended feeding periods contribute to osteogenesis. In batch-reared fish, total OTC and 4-epioxytetracycline peak concentrations in muscle tissue did not significantly differ among treatments but were significantly greater for smaller individuals within treatments suggesting that the OTC uptake and elimination response is mechanistically related to higher gill ventilation volume and gastric ingestion rate of small fish providing increased chemical assimilation and decreased clearing time following OTC immersions. Increased otolith mark quality derived from such feeding protocols may be of particular interest to fisheries managers conducting stock contribution assessments of yellow perch, but this induction strategy may apply to other species as well as therapies for hatchery stocks.

Design of a Ka‐Band Microstrip Antenna Array with Sharped‐Beam Pattern and High Gain

ABSTRACTA Ka‐band microstrip array antenna is presented in this article. It operates at 35.1 GHz and can realize sharped‐beam pattern and high gain. The antenna array consisting of 14 ×8 elements is fabricated on Rogers RT5880 substrate with 0.254‐mm thickness. It is center‐fed by a coax probe, and the symmetrical feed network is two‐stage cascaded with unequal amplitudes and the same phase. The total size of the array is 110 ×67 mm2. The simulated and test results show that the antenna array has a gain of 25 dB, the 3 dB beamwidths in azimuth, and elevation plane are less than 6° and 10° respectively, the sub lobe suppression is −18 dB. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2517–2520, 2013

Hydrogen production by supercritical water gasification of biomass: Particle and residence time distribution in fluidized bed reactor

Particle distribution and residence time distribution (RTD) in supercritical water fluidized bed reactor (SCWFBR) greatly affect the hydrogen yield through determining the two phase mixing and reaction time. A Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the solid distribution and RTD of feeding materials. The effect of four types of feeding methods and feeding rates on solid distribution and RTD were evaluated based on the simulation results. Results showed that double symmetrical feeding pipe with an feeding mouth angle of 45° provides more uniform solid distribution and longer residence time compared with those of other three types. A nonlinear relationship between feeding rate and RTD was observed, and an optimum feeding rate was found to be related to the best solid-fluid mixing in the study.

Design of wide‐stopband microstrip bandpass filter with assistance of spur lines

A novel microstrip bandpass filter with compact size is proposed. With two short-circuited stubs, one open-circuited coupled line using symmetrical feeding, and two spur lines, a wide passband can be obtained. Detailed design and synthesis procedures are provided for filter development. Moreover, the electromagnetic simulator IE3D is used; the prototype of the bandpass filter is consequently fabricated and measured. Agreement between measured results and the theoretical prediction validates the proposed structure.

User effect comparison between metal bezel antenna and planar inverted F‐antenna for mobile terminal

AbstractThis article presents a novel metal bezel antenna structure and its performance in user vicinity. The antenna is designed by keeping in mind the insensitivity in usage environments. In the antenna structure, a mobile chassis and a bezel are combined as one antenna element. Symmetrical feeding is used to excite the antenna. The characteristics of the metal bezel are compared with those of a conventional planar inverted‐F antenna in terms of user effect at E‐GSM band (880–960 MHz). Both antennas are measured and compared with four different hand phantom grips representing a browsing mode. The grips are designed so that the chassis is under the hand phantom in different variable usage conditions. Results are compared in terms of S11, total efficiency, total body loss, radiation efficiency, reflection loss, and in Smith chart presentation. Finally, antenna structures are compared with hand and head phantom measurements representing a calling mode. The comparison is done in terms of average total body loss. The used hand grips are the same as in the case of the hand phantom measurements. © 2012 Wiley Periodicals,v Inc. Microwave Opt Technol Lett 55:316–322, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27306

A Balun-Bandpass filter with good in-band performance and wide stopband

A high performance Balun BandPass Filter (BPF) with capacitively loaded multiple coupled lines with very simple structure is proposed in this paper, this structure realizes simultaneous size reduction and superior harmonic response suppression performance in bandpass filtering meanwhile good differential performance of the Balun. The theory of this structure for unbalanced input into balanced output has been studied in this paper and a proper Balun and BPF characteristic by the symmetric feeding and skew symmetric feeding have been obtained to prove the theory. The enter frequency of the fabricated Balun-BPF is operated at 2.45 GHz with 6.93% Fractional Band Width (FBW), and this frequency is used for Bluetooth and some other communication systems. The differences between the two outputs are 180° ± 1.92° in phase and within 0.33 dB in magnitude. At f0, the amplitude imbalance and phase difference are within 0.25 dB and 180.86°, respectively. The measured frequency responses agree well with the simulated ones. With the theoretical analyses and practical results, it is shown that the proposed one has the advantages of simple structure, convenient analysis and good performance of both BPF and Balun.

A HIGH PERFORMANCE BALUN BANDPASS FILTER WITH VERY SIMPLE STRUCTURE

A high performance balun bandpass fllter (BPF) with very simple structure is proposed in this letter, this structure realizes superior performance in bandpass flltering meanwhile with good difierential performance of the balun. The proper balanced outputs and BPF characteristic by the symmetric feeding and skew-symmetric feeding have been obtained, and the theory of this simple structure for unbalanced input to balanced outputs has been studied. The center frequency of the fabricated balun-BPF was operated at 2.4GHz with 5.8% fractional bandwidth (FBW), and this frequency is used for Bluetooth and some other communication systems. The difierences between the two outputs are 180 - § 5 - in phase and within 0.39dB in magnitude. At f0, the amplitude imbalanced and phase difierence are within 0.37dB and 179.2 - , respectively. The measured frequency responses agree well with the simulated ones. With the theoretical analyses and practical results, it is shown that the proposed one has the advantages of simple structure, convenient analysis and good performance of both BPF and balun.

Design of a microstrip bandpass filter with wide stopband

AbstractIn this work, a novel microstrip bandpass filter with a wide stopband is proposed. With the assistance of an open stub, one modified open‐circuit coupled line with symmetrical feeding, a long transmission line, and a wide stopband with a sufficient rejection level can be achieved. Detailed design and synthesis procedures are provided. Good agreement between simulation and measurement demonstrates feasibility of the proposed filter. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:549–551, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26557

The Current Distribution of Symmetrical Dual and Triple Feeding Full-Wave Dipole Antenna

This paper is focused on the analysis of the current distribution of symmetrical full-wave dipole antenna based on double and triple feeding techniques; the current distributions were measured using a shielded loop protruding through a slit in the antenna surface along its axis, gives exact and accurate measurement rather than sinusoidal approximation. However, the sinusoidal distributions of current and voltage are approximations rather than exact descriptions. Next the current distributions were modeled and formulated whose parameters were deduced from the measured current distribution by applying the current distribution data in models as derived by IEEE standard

Creation of a Magnetic Boundary Condition in a Radiating Ground Plane to Excite Antenna Modes

The creation of a magnetic boundary condition into the plane of symmetry in a radiating ground plane of a portable device is proposed to enhance its radiation efficiency and bandwidth. This magnetic boundary condition is achieved by exciting the antenna through symmetrical feeding. A novel antenna consisting of a symmetrical folded dipole is presented in order to exemplify how a broad bandwidth and very good radiation properties can be obtained with the proposed technique. The Theory of Characteristic Modes is used to analyze and compare a folded dipole with the symmetrical folded dipole. This study shows how the magnetic boundary condition favors excitation of antenna modes in a broad bandwidth while avoiding excitation of transmission line modes. Two different prototype antennas, a monopole and a symmetrical folded dipole with an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -balun, were implemented and measured. The measured -6 dB impedance bandwidth of the monopole extends from 0.95 GHz to 2.15 GHz. In turn, the bandwidth of the symmetrical folded dipole extends from 0.90 GHz to 1.96 GHz. The average of the measured total efficiencies at the aforementioned bandwidth is -1.6 dB for both prototypes. The measured maximum total gain at 0.95 GHz is 2.6 dBi for the monopole and 1.9 dBi for the symmetrical folded dipole.

Concentration and fractionation by isoelectric trapping in a micropreparative‐scale multicompartmental electrolyzer having orthogonal pH gradients. Part 2

A micropreparative-scale multicompartmental electrolyzer called ConFrac has been developed and tested for isoelectric trapping separations. ConFrac can be operated in pass-by-pass mode or recirculating mode, using either asymmetrical feeding (feed enters only the anodic or the cathodic flow-through compartment) or symmetrical feeding (feed enters both the anodic and the cathodic flow-through compartment). Symmetrical feeding results in higher processing rates and is the preferred operation mode. Residence time in the flow-through compartments is set as a compromise between processing rate and temperature rise in the effluent. Ampholytic components have been isolated from 5 to 50 mL volumes of micromolar feed solutions and hundredfold concentrated into 100-μL collection compartments. Samples containing ampholytic analytes in highly conducting salt solutions were readily desalted and fractionated in ConFrac in one operation. pH transients formerly observed in other isoelectric trapping devices were observed in ConFrac as well. The pH transients were caused by the unequal ion transmission rates of the anodic- and cathodic-side buffering membranes.

A Cross-Shaped Dielectric Resonator Antenna for Multifunction and Polarization Diversity Applications

This letter proposes a multifunction cross-shaped dielectric resonator antenna (DRA) with separately fed broadside circularly polarized (CP) and omnidirectional linearly polarized (LP) radiation patterns. These distinct radiation patterns are achieved in overlapping frequency bands by exciting two different modes in a single dielectric resonator (DR) volume. This letter also investigates the effect of the feeding geometry on the mutual coupling between the modes and concludes that an asymmetric feeding degrades the orthogonality of the modes and thus increases the interport coupling coefficient. By using a symmetric feeding, the coupling coefficient can be significantly reduced to below - 30 dB in the frequency band common to both operation modes. The experimental results show a good agreement with simulation and demonstrate a broadside CP operation over a bandwidth of 6.8%, which overlaps with the omnidirectional LP impedance bandwidth of 38.5%. The proposed antenna could be used not only as multifunction, but also as polarization diversity antenna due to the overlapping dual-feed CP and LP operation.

Dual-Polarized Corrugated Horns for Advanced Measurement Applications

Recent advances in the design of orthomode junctions (OMJs) have created new devices capable of achieving as much as a 1:4 bandwidth, while maintaining the high performance of traditional OMJ designs. The new OMJ technology is based on an inverted-ridge structure, with four symmetrical feeding points for external balanced feeding, stabilizing the frequency dependence of the OMJ. This paper discusses the achievable performance and limitations of wideband probes with multiple corrugated apertures. It shows measured and predicted design examples of apertures covering up to 1:2 bandwidth in the L- to Ka-band range.

High-Speed Operation of a Gas-Bearing Supported MEMS-Air Turbine

Silicon based power micro-electro-mechanical system (MEMS) applications require high-speed microrotating machinery operating stably over a large range of operating conditions. The technical barriers to achieving stable high-speed operation with micro-gas-bearings are governed by (1) stringent fabrication tolerance requirements and manufacturing repeatability, (2) structural integrity of the silicon rotors, (3) rotordynamic coupling effects due to leakage flows, (4) bearing losses and power requirements, and (5) transcritical operation and whirl instability issues. To enable high-power density the micro-turbomachinery must be run at tip speeds comparable to conventional scale turbomachinery. The rotors of the micro-gas turbines are supported by hydrostatic gas journal and hydrostatic gas thrust bearings. Dictated by fabrication constraints the location of the gas journal bearings is at the outer periphery of the rotor. The high bearing surface speeds (target nearly 10×106 mm rpm), the very low bearing aspect ratios (L/D&lt;0.1), and the laminar flow regime in the bearing gap (Re&lt;500) place these micro-bearing designs into unexplored regimes in the parameter space. A gas-bearing supported micro-air turbine was developed with the objectives of demonstrating repeatable, stable high-speed gas-bearing operation and verifying the previously developed micro-gas-bearing analytical models. The paper synthesizes and integrates the established micro-gas-bearing theories and insight gained from extensive experimental work. The characteristics of the new micro-air turbine include a four-chamber journal bearing feed system to introduce stiffness anisotropy, labyrinth seals to avoid rotordynamic coupling effects of leakage flows, a reinforced thrust bearing structural design, a redesigned turbine rotor to increase power, a symmetric feed system to avoid flow and force nonuniformity, and a new rotor micro-fabrication methodology for reduced rotor imbalance. A large number of test devices were successfully manufactured demonstrating repeatable bearing geometry. More specifically, three sets of devices with different journal bearing clearances were produced to investigate the dynamic behavior as a function of bearing geometry. Experiments were conducted to characterize the “as-fabricated” bearing geometry, the damping ratio, and the natural frequencies. Repeatable high-speed bearing operation was demonstrated using isotropic and anisotropic bearing settings reaching whirl-ratios between 20 and 40. A rotor speed of 1.7×106 rpm (equivalent to 370 m/s blade tip speed or a bearing DN number of 7×106 mm rpm) was achieved demonstrating the feasibility of MEMS-based micro-scale rotating machinery and validating key aspects of the micro-gas-bearing theory.

Design of an Efficient X-Band Waveguide-Fed Microstrip Patch Array

The design and fabrication of a 10.5 GHz microstrip patch array fed by a waveguide is presented. The gain of this antenna is 29 dB and its efficiency is 65%. Commonly, the efficiency of conventional microstrip arrays at X-band is not more than 50%. This antenna demonstrates the ability to accomplish a very high efficiency at X-band in a simple structure. This is achieved by using a slotted waveguide to feed the planar array. To allow symmetrical feed of this antenna, the waveguide is a center-fed slotted waveguide, the two ends of which are shorted. The design procedure is expatiated, which contains the study and design of the waveguide-fed subarray structure and of the coax-to- waveguide transition structure. For designing this entire antenna, a three-dimensional electromagnetic field simulation software CST Microwave Studio is applied. Good agreement is achieved between measurement and simulation results.

Enhanced Stop-band Rejection by Symmetric Feeding in 1.8 GHz Cross-coupled Planar HTS Microwave Filters

The superior performance manifested in characteristics of low pass-band insertion loss, high stop-band rejection, and sharp band edge skirt, has led the superconducting microwave fllters one of the most attractive candidates for wireless communication applications. In this paper, we report the design and fabrication of the 4-poles cross-coupled planar microwave fllters fabricated using YBCO superconducting thin fllms deposited on both sides of a LAO single crystal substrate by pulsed laser deposition. The resonator geometry allows one to miniaturize the 1.8GHz fllters onto a substrate with dimensions of 1cm£1cm. We also demonstrate that by properly choosing the feeding conflguration, fllters with better selectivity, in particular with an additional pair of deep transmission zeros (poles) outside both sides of pass-band, can be achieved. DOI: 10.2529/PIERS060906091103

Expansion of existing EM workbench for multiple computational electromagnetics codes

An workbench is described. It has a modular, code-independent architecture and a common design environment. The technique for integrating new EM codes is demonstrated with a method-of-moments code specialized for circularly symmetric feed horns, and with a new hybrid DFT-MoM (discrete Fourier transform - method of moments) code for finite-boundary planar phased arrays. The use of a common design environment for all codes takes advantage of common infrastructure and utility software, and minimizes the learning-curve penalty for using a new EM code capability.

Spherical wave blockage in reflector antennas

The effects of the spherical wave blockage in reflector antennas is investigated. This problem is likely to occur in axially symmetrical feed antennas of single- and dual-reflector type in both single- and dual-reflector configurations, owing to the presence of primary feeds and their supports including struts that are normally placed between the primary source and the main reflector. The main reflector blockage due to large obstacles is estimated by the well-known null-field technique that employs flat polygonal plate models of the masking structures to define the obscured area. Although this same approach may be used to predict the spherical wave blockage due to the struts, a more rigorous but yet efficient technique is also employed, which consists of superimposing to the primary field the high-frequency scattered field from the struts. This field is calculated by using scattering coefficients that are derived by locally approximating the actual structure, by an infinite circular cylinder. This latter formulation is compared with the null-field technique and validated by an experimental campaign. The measurement setup is particularly useful for isolating spherical wave-blockage effects. It consists of a single-reflector offset antenna where a single strut is mounted with its axis parallel to that of the focusing parabola, thus, practically enforcing the plane wave blockage to vanish. Comparisons with the measurements have shown that the null-field approach is adequate for predicting the secondary pattern for large polygonal obstacle, but it is unsatisfactory to treat the strut blockage. It is found that this latter can be successfully described with the more rigorous high-frequency approach.