Spl Deg Research Articles

A simple and low-cost fabrication of polymeric vertical microlens using dip method

Polymeric vertical microlenses (PVMs) using photoresist material SU-8 are fabricated with a simple and low-cost process that can be easily applied to the microoptical/optoelectronic bench. By virtue of the strong adhesive force and liquid cohesion, the PVMs are formed by hanging the liquid SU-8 on walls by a dip method. Then, in order to enhance the thermal stability and reliability of the PVMs, the lenses are baked and exposed in the ultraviolet light to crosslink the SU-8. To characterize the PVMs, we use a single-mode fiber carrying a 1.55-μm wavelength laser light source and utilize BeamScope P5 to observe the beam convergences. The output beams through the PVMs show a vertical far-field angle of 3.04/spl deg/, as compared to 5.53/spl deg/ of the beam without passing through the lenses.

A multiband /spl Delta//spl Sigma/ fractional-N frequency synthesizer for a MIMO WLAN transceiver RFIC

This work presents a shared fractional-N synthesizer used by two dual-band 802.11 radios integrated on a single chip for 2/spl times/2 multiple-input multiple-output (MIMO) applications. Additional 2/spl times/2 MIMO chips can be used in a system by phase synchronizing the signal paths through a bidirectional LO porting scheme developed for this application. This synthesizer was fully integrated with the exception of an off-chip loop filter. The synthesizer is a /spl Delta//spl Sigma/-based fractional-N frequency synthesizer with three on-chip LC tuned VCOs to cover the entire frequency bands specified in the IEEE 802.11a/b/g and Japanese WLAN standards. The radio uses a variable IF frequency so that both the RF LO and IF LO can be derived from a single synthesizer saving chip area and power. The synthesizer includes a programmable second/third-order /spl Delta//spl Sigma/ noise shaper, a phase frequency detector, a differential charge pump, and a 6-bit multimodulus divider (MMD). The nominal jitter from 100 Hz to 10 MHz is 0.63-0.86/spl deg/ rms in the 5-GHz band and 0.35-0.43/spl deg/ rms in the 2.4-GHz band. The maximum frequency deviation of the synthesizer when enabling the transmitter is less than 150 kHz and the frequency error settles to 2 kHz in less than 12 /spl mu/s. For MIMO applications requiring more than two full paths, a single synthesizer on one die can be used to generate the LOs for all other radios integrated in different dies.

Double-beam parallel-plate slot antenna

This paper presents the design and prototyping of a double-beam linear polarized parallel-plate slot antenna at 12-GHz band. Each beam is separated 27.7/spl deg/ and 27.3/spl deg/, respectively, from broadside direction. Two different radiation patterns are generated, exciting the parallel plate from opposite sides. The radiating elements are composed by three parallel slots, the central slot is close to the resonance, while the side ones are designed to minimize the reflection inside the parallel plate. The length of the slots in the same row is kept constant (periodic walls), and the distance between columns is equal to 0.7 times the wavelength. The designs of the feeding networks and the design of the array of slots generate both beams, pointing toward Hispasat and Astra satellites simultaneously, at the same frequency band. The feeding networks are two microstrip circuits that excite two linear arrays of 24 patches, placed at both sides of the antenna, and generate both quasi-TEM mode plane waves inside the parallel-plate waveguide, propagating from one side to the other.

Return loss reduction of integrated grating-assisted optical add/drop multiplexer by control of the reflective spectrum

Return loss, a key characteristic of the optical add/drop multiplexer (OADM), has become an urgent and challenging problem in the development of the integrated grating-assisted OADM. In this paper, a novel design approach to achieve low-return-loss integrated grating-assisted OADMs is proposed. The reflective spectrum is properly controlled to ensure the backreflection peaks can fall outside the wavelength channel, so that the return loss can be kept low. Meanwhile, it can also be found that the tolerance in fabrication process is enlarged. Simulation on the null-coupler OADM shows that, by employing the proposed method, the return loss at both input- and add-port can drop to lower than -53 dB from -38 and 0 dB, respectively, and be kept below -53 dB even with a tilt angle ranging from 3.2/spl deg/ to 3.5/spl deg/. The application of this method on the design of the symmetric-coupler OADM is also presented.

A 12-GHz SiGe phase shifter with integrated LNA

This paper presents the design and measurement of a 12-GHz active phase shifter with an integrated low-noise amplifier in SiGe. The phase is controlled with a 1-bit (180/spl deg/) digital phase shifter and a 180/spl deg/ continuous analog phase shifter. The 1-bit digital phase shifter is implemented by switching between a -90/spl deg/ low-pass network and a +90/spl deg/ high-pass network. The analog phase shifter is implemented using a lumped-element loaded line technique where both series and shunt elements are adjusted to continuously vary the phase while maintaining a constant port impedance. Design equations for this constant-impedance phase-shift network are derived and presented. The phase shifter achieves 3.7/spl plusmn/0.5 dB of gain, with a noise figure of 4.4 dB at a center frequency of 11.5 GHz. The total chip size including pads is 1920 /spl mu/m /spl times/ 780 /spl mu/m, and the area of the active circuitry without pads is 1680 /spl mu/m /spl times/ 660 /spl mu/m (1.1 mm/sup 2/).

A novel design tool for waveguide polarizers

This paper presents a novel method for the design of broad-band waveguide polarizers. It consists of an interactive procedure where the designer places the zeros of the reflection coefficient for one polarization, simultaneously also controlling the frequency response of the other one and vice versa. In this way, the best matching condition for both polarizations can be found. This design tool is based on an automated phase control procedure and on an algorithmic characterization of the relationship between the two frequency responses. The spurious effects of multimodal interactions, frequency dispersion, and losses are taken into account and compensated by characterizing them with suitable transfer functions. Designs of iris-loaded polarizers in square and circular waveguides are described, with operative bandwidths up to 30%. Measurements on a 10% bandwidth Ka-band prototype show reflection and cross-polarization levels of approximately -50 dB, with a phase error of approximately 0.4/spl deg/.

User-interactive registration of bone with A-mode ultrasound

In this study, we investigated a registration technique based on a mechanically tracked A-mode ultrasound pointer for transcutaneous A-mode ultrasound pointer for transcutaneous, noninvasive palpation of bone surface. The principle has been exemplified for distal femur registration in total hip replacement surgery and has been evaluated in laboratory trials on a bone/soft-tissue model. Three different registration modes were demonstrated. Regarding clinical requirements, we constricted the areas of palpation to points and surfaces accessible through a minimal surgical portal in order to avoid additional trauma to soft tissue. Registration based solely on proximal surface points seems to be insufficient for clinical application. To avoid the invasive direct palpation of the condyles and epicondyles, we used the A-mode ultrasound pointer for noninvasive transcutaneous registration (Mode III). The resulting entire mean rms error was 0.59 mm (0.28/spl deg/), which is significantly better and more reliable than a registration exclusively in the proximal part of the femur. During the ultrasound registration process, the computer-based assistance tool gave visual feedback to the user to guide the alignment of the transducer's beam axis to be perpendicular to the local bone surface. After five iterations, the final angle error of this approximation was in the range of /spl plusmn/2 degree and generally influenced by the contribution of the discretization angle error /spl Phi//sub DIS/. Based on the consideration of the thickness of the soft-tissue and the geometry of the ultrasound probe, it is suggested that this is a sufficient accuracy in order to ensure a reliable ultrasound-based digitization of the bone surface. The overall mean registration time using A-mode ultrasound, including palpation, and matching, seems to be tolerable. The algorithm and interface for user-interactive A-mode ultrasound-based registration seem to provide efficient support for robust and accurate registration.

660-nm GaInP-AlGaInP quantum-well laser diode structures with reduced vertical beam divergence angle

We propose a new layer design for 660-nm GaInP-AlGaInP quantum-well laser diodes employing a two-step n-cladding layer and demonstrate the feasibility of achieving a reduced vertical beam divergence angle of as low as 14.8/spl deg/ with a relatively small decrease in the optical confinement factor by theoretical simulations and experimental observations.

A 2.5-GHz eight-phase VCO in SiGe BiCMOS technology

We present a 2.5-GHz voltage-controlled oscillator (VCO) with eight equally distributed phases derived from a 10-GHz LC VCO. Stochastic and static phase errors were obtained by spectrum analyzer measurements in conjunction with an on-chip single-sideband mixer. From the measured phase noise spectrum, we predict an absolute rms jitter contribution of 130 fs in a 2-MHz bandwidth phase-locked loop. A static phase error of less than 0.7/spl deg/ was deduced from the sideband suppression. The eight-phase VCO is tunable from 2.35 to 2.85 GHz and draws 16 mA from a 2.0-V supply. Possible applications include clock and data recovery of a 10-Gb/s signal in a fiber-optic receiver as well as high-precision image rejection receivers and I/Q direct up-converters for radio-frequency applications.

Microwave backscatter modeling of erg surfaces in the Sahara desert

The Sahara desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter (/spl sigma//spl deg/) modulation with azimuth angle (f). We use /spl sigma//spl deg/ measurements observed at various incidence angles and f from the NASA Scatterometer (NSCAT), the SeaWinds scatterometer, the ERS scatterometer (ESCAT), and the Tropical Rainfall Measuring Mission's Precipitation Radar to model the /spl sigma//spl deg/ response from sand dunes. Observations reveal a characteristic relationship between the backscatter modulation and the dune type, i.e., the number and orientation of the dune slopes. Sand dunes are modeled as a composite of tilted rough facets, which are characterized by a probability distribution of tilt with a mean value, and small ripples on the facet surface. The small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at Bragg angles only. Longitudinal and transverse dunes are modeled with rough facets having Gaussian tilt distributions. The model results in a /spl sigma//spl deg/ response similar to NSCAT and ESCAT observations over areas of known dune types in the Sahara. The response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere. This analysis provides a unique insight into scattering by large-scale sand bedforms.

Observation and characterization of radar backscatter over Greenland

Characterization of the microwave signature of the Greenland snow surface enables delineation of the different snow facies and is a tool for tracking the effects of climate change. A new empirical observation model is introduced that uses a limited number of parameters to characterize the snow surface based on the dependence of radar backscatter on incidence angle, azimuth angle, spatial gradient, and temporal rate of change. The individual model parameters are discussed in depth with examples using data from the NASA Scatterometer (NSCAT) and from the C-band European Remote Sensing (ERS) satellite Advanced Microwave Instrument in scatterometer mode. The contribution of each model term to the overall accuracy of the model is evaluated. The relative contributions of the modeled dependencies vary by region. Two studies illustrating applications of the model are included. First, interannual changes over the Greenland ice sheet are investigated using nine years of ERS data. Surface changes are observed as anomalies in the /spl sigma//spl deg/ model parameters. Second, intraannual variations of the surface are investigated. These changes are observed in the average backscatter normalized to a given observation geometry. The results indicate that the model can be used to obtain a more complete understanding of multiyear change and to obtain low-variance high temporal resolution observations of intraannual changes. The model may be applied for increased accuracy in scatterometer, synthetic aperture radar (SAR), and wide-angle SAR studies.

Spatial filter-based absorbing boundary for the 2-D digital waveguide mesh

The digital waveguide mesh is a method for simulating wave propagation, for example, in an acoustic system. Research on the boundary conditions has been going on for years, but adequate solutions for absorbing boundaries have not yet been presented for the digital waveguide mesh. In this work, a new method for constructing absorbing boundaries for a two-dimensional (2-D) rectangular mesh is introduced. With the use of the proposed numerically optimized spatial filtering with an interpolated mesh structure, the reflection was diminished to under -25 dB at incidence angles |/spl theta/|/spl les/79.26/spl deg/ on a frequency band limited only at the very lowest and highest ends.

Laser cleaving of glass fibers and glass fiber arrays

An ultraviolet (UV)-excimer-laser-based cleaving procedure for silica fiber has been developed that enables automated cleaving for high-volume production of fiber-optic assemblies. A selective ablation of the glass in the form of a small rectangular cavity serves as a fracture initiator when the fiber is put under stress. The position of the UV-excimer-laser-induced scratch is very precise. The system provides high-quality cleaves on single-fiber and ribbon configurations. The end angle of the cleaved optical fiber is measured using a noncontact optical interferometer system and was 0.85/spl deg/ for perpendicular cleavages. Insertion loss after splicing is in the range of 0.03 dB, which is compatible with mechanical-cleaved fibers.

A 0.25-/spl mu/m CMOS OPLL transmitter IC for GSM and DCS applications

A single-chip CMOS global system for mobile communications/digital cellular system dual-band offset phase-locked loop (OPLL) transmitter is presented in this paper. This chip includes a quadrature modulator and an OPLL modulation loop. Except for the loop filter and high-power voltage-controlled oscillator (TX VCO), everything is integrated into this chip to form a dual-band transmitter. This transmitter integrated circuit is fabricated in a 0.25-/spl mu/m CMOS process. The current consumption without the TX VCO is approximately 23 mA under 2.7-V power supply for both bands. The measured rms and peak phase errors for Gaussian minimum shift-keying (GMSK) modulated signals are approximately 1/spl deg/ and 2.4/spl deg/, respectively. The measurements show comparable performance to its BiCMOS counterparts.

A hybrid strategy to solve the forward kinematics problem in parallel manipulators

A parallel manipulator is a closed kinematic structure with the necessary rigidity to provide a high payload to self-weight ratio suitable for many applications in manufacturing, flight simulation systems, and medical robotics. Because of its closed structure, the kinematic control of such a mechanism is difficult. The inverse kinematics problem for such manipulators has a mathematical solution; however, the forward kinematics problem (FKP) is mathematically intractable. This work addresses the FKP and proposes a neural-network-based hybrid strategy that solves the problem to a desired level of accuracy, and can achieve the solution in real time. Two neural-network (NN) concepts using a modified form of multilayered perceptrons with backpropagation learning were implemented. The better performing concept was then combined with a standard Newton-Raphson numerical technique to yield a hybrid solution strategy. Simulation studies were carried out on a flight simulation syystem to check the validity o the approach. Accuracy of close to 0.01 mm and 0.01/spl deg/ in the position and orientation parameters was achieved in less than two iterations and 0.02 s of execution time for the proposed strategy.

A design of wideband 3-dB coupler with N-section microstrip tandem structure

New design equations and a 3-dB microstrip coupler example for N-section tandem connected structure with wide bandwidth are presented. The proposed four-port S-parameters and equations are obtained from a port reduction method. The designed microstrip 3-dB coupler not only does not need high impedance lines, but also uses tight coupling gaps differently from conventional couplers such as Lange couplers, parallel coupled line couplers, etc. The measured data agrees well with the expected data, which show a wide bandwidth of 42%, an amplitude imbalance of /spl plusmn/0.5 dB, a phase unbalance of 1.0/spl deg/, and isolation characteristics of 15 dB at the band of 3.6 to 5.5 GHz.

A broadband Wilkinson balun using microstrip metamaterial lines

A metamaterial balun that converts a single-ended input to a differential output over a large bandwidth is presented. The device also exhibits excellent return loss, isolation, and through characteristics over the same frequency band. The balun comprises a Wilkinson divider, followed by a +90/spl deg/ negative-refractive-index (NRI) metamaterial (MM) phase-shifting line along the top branch, and a -90/spl deg/ MM phase-shifting line along the bottom branch. Utilizing MM lines for both the +90/spl deg/ and -90/spl deg/ branches allows the slopes of their phase responses to be matched, resulting in a broadband differential output signal. The theoretical performance of the balun is verified through circuit simulations and measurements of a fabricated prototype at 1.5 GHz. The MM balun exhibits a measured differential output phase bandwidth (180/spl deg//spl plusmn/10/spl deg/) of 1.16 GHz (77%), from 1.17 to 2.33 GHz. The measured isolation and return loss for all three ports remain below -10 dB over a bandwidth in excess of 2 GHz, while the output quantities |S/sub 21/| and |S/sub 31/| remain above -4 dB from 0.5 to 2.5 GHz.

Parallel plate waveguide antenna for point-to-multipoint communication at millimetre-wave frequencies

Simulation and measurement results for a parallel plate waveguide antenna designed for a point-to-multipoint communication system at millimetre-wave frequencies is presented. The antenna consists of a waveguide feed, an H-plane horn, an enclosed parabolic reflector, a rectangular waveguide containing irises, and corrugated baffles. Half power beamwidths between 4.9/spl deg/-6.0/spl deg/ in elevation and 58/spl deg/-79/spl deg/ in azimuth are achieved for a bandwidth of 13%. The gain varies between 19 and 20 dBi for the frequency range between 21 and 25 GHz. The manufactured antenna is very compact with a size of 200/spl times/147/spl times/50 mm.

A novel broadband polarization diversity antenna using a cross-pair of folded dipoles

A /spl plusmn/45/spl deg/ polarization diversity antenna with wide bandwidth is presented in this letter. The antenna has a half-power beam width of 65/spl deg/ in the horizontal plane for use in wireless telecommunication base stations. Especially, a folded dipole antenna with a protruding part is used as a +45/spl deg/ polarization element and the another folded dipole with a concave part is used as a -45/spl deg/ polarization element. The protruding part and the concave part of dipoles make the two folded dipoles with the same height but not touching each other. With such a cross-pair of folded dipoles, a small polarization diversity antenna is constructed. The antenna was analyzed and optimized by the high frequency structure simulation software, and a good agreement was achieved between computation and experiments on the half-power beam width in the horizontal plane.

A novel demodulation scheme for fiber Bragg grating sensor system

A novel fiber Bragg grating (FBG) wavelength demodulation scheme based on a compound interference configuration is introduced. This scheme measures the strain-induced wavelength-shift of the FBG in terms of phase-shift signal. The sensing resolution and sensitivity were demonstrated to be 6.2 n/spl epsiv/ and 1.59/spl deg///spl mu//spl epsiv/, respectively, which match the theoretical value of 1.61/spl deg///spl mu//spl epsiv/ very well.