77,114 research outputs found
Reflective Toraldo pupil for high-resolution millimeter-wave astronomy
A novel, to the best of our knowledge, beam-shaping reflective surface for high-resolution millimeter/ submillimeter-wave astronomy instruments is presented. The reflector design is based on Toraldoâs superresolution principle and implemented with annulated binary-phase coronae structure inspired by the achromatic magnetic mirror approach. A thin, less than half a free-space wavelength, reflective Toraldo pupil device operated in the W-band has been fabricated using mesh-filter technology developed at Cardiff University. The device has been characterized on a quasi-optical test bench and demonstrated expected reduction of the beam width upon reflection at oblique incidence, while featuring a sidelobe level lower than â10 dB. The proposed reflective Toraldo pupil structure can be easily scaled for upper millimeter and infrared frequency bands as well as designed to transform a Gaussian beam into a flat-top beam with extremely low sidelobe level
The Beauty of Symmetry: Common-mode rejection filters for high-speed interconnects and balanced microwave circuits
Common-mode rejection filters operating at microwave frequencies have been the
subject of intensive research activity in the last decade. These filters are of interest for
the suppression of common-mode noise in high-speed digital circuits, where differential
signals are widely employed due to the high immunity to noise, electromagnetic
interference (EMI) and crosstalk of differential-mode interconnects. These filters can
also be used to improve common-mode rejection in microwave filters and circuits
dealing with differential signals. Ideally, common-mode stopband filters should be
transparent for the differential mode from DC up to very high frequencies (all-pass),
should preserve the signal integrity for such mode, and should exhibit the widest and
deepest possible rejection band for the common mode in the region of interest.
Moreover, these characteristics should be achieved by means of structures with the
smallest possible size. In this article, several techniques for the implementation of
common-mode suppression filters in planar technology are reviewed. In all the cases,
the strategy to simultaneously achieve common-mode suppression and all-pass behavior
for the differential mode is based on selective mode-suppression. This selective mode
suppression (either the common or the differential mode) in balanced lines is typically
(although not exclusively) achieved by symmetrically loading the lines with symmetric
resonant elements, opaque for the common-mode and transparent for the differential
mode (common-mode suppression), or vice versa (differential-mode suppression).MINECO, Spain-TEC2013-40600-R, TEC2013-41913-PGeneralitat de Catalunya-2014SGR-15
Digital carrier demodulator employing components working beyond normal limits
In a digital device, having an input comprised of a digital sample stream at a frequency F, a method is disclosed for employing a component designed to work at a frequency less than F. The method, in general, is comprised of the following steps: dividing the digital sample stream into odd and even digital samples streams each at a frequency of F/2; passing one of the digital sample streams through the component designed to work at a frequency less than F where the component responds only to the odd or even digital samples in one of the digital sample streams; delaying the other digital sample streams for the time it takes the digital sample stream to pass through the component; and adding the one digital sample stream after passing through the component with the other delayed digital sample streams. In the specific example, the component is a finite impulse response filter of the order ((N + 1)/2) and the delaying step comprised passing the other digital sample streams through a shift register for a time (in sampling periods) of ((N + 1)/2) + r, where r is a pipline delay through the finite impulse response filter
MKID development for SuperSpec: an on-chip, mm-wave, filter-bank spectrometer
SuperSpec is an ultra-compact spectrometer-on-a-chip for millimeter and
submillimeter wavelength astronomy. Its very small size, wide spectral
bandwidth, and highly multiplexed readout will enable construction of powerful
multibeam spectrometers for high-redshift observations. The spectrometer
consists of a horn-coupled microstrip feedline, a bank of narrow-band
superconducting resonator filters that provide spectral selectivity, and
Kinetic Inductance Detectors (KIDs) that detect the power admitted by each
filter resonator. The design is realized using thin-film lithographic
structures on a silicon wafer. The mm-wave microstrip feedline and spectral
filters of the first prototype are designed to operate in the band from 195-310
GHz and are fabricated from niobium with at Tc of 9.2K. The KIDs are designed
to operate at hundreds of MHz and are fabricated from titanium nitride with a
Tc of 2K. Radiation incident on the horn travels along the mm-wave microstrip,
passes through the frequency-selective filter, and is finally absorbed by the
corresponding KID where it causes a measurable shift in the resonant frequency.
In this proceedings, we present the design of the KIDs employed in SuperSpec
and the results of initial laboratory testing of a prototype device. We will
also briefly describe the ongoing development of a demonstration instrument
that will consist of two 500-channel, R=700 spectrometers, one operating in the
1-mm atmospheric window and the other covering the 650 and 850 micron bands.Comment: As submitted, except that "in prep" references have been update
Band-pass filtering of the time sequences of spectral parameters for robust wireless speech recognition
In this paper we address the problem of automatic speech recognition when wireless speech communication systems are involved. In this context, three main sources of distortion should be considered: acoustic environment, speech coding and transmission errors. Whilst the first one has already received a lot of attention, the last two deserve further investigation in our opinion. We have found out that band-pass filtering of the recognition features improves ASR performance when distortions due to these particular communication systems are present. Furthermore, we have evaluated two alternative configurations at different bit error rates (BER) typical of these channels: band-pass filtering the LP-MFCC parameters or a modification of the RASTA-PLP using a sharper low-pass section perform consistently better than LP-MFCC and RASTA-PLP, respectively.Publicad
Eigenfilters: A new approach to least-squares FIR filter design and applications including Nyquist filters
A new method of designing linear-phase FIR filters is proposed by minimizing a quadratic measure of the error in the passband and stopband. The method is based on the computation of an eigenvector of an appropriate real, symmetric, and positive-definite matrix. The proposed design procedure is general enough to incorporate both time- and frequency-domain constraints. For example, Nyquist filters can be easily designed using this approach. The design time for the new method is comparable to that of Remez exchange techniques. The passband and stopband errors in the frequency domain can be made equiripple by an iterative process, which involves feeding back the approximation error at each iteration. Several numerical design examples and comparisons to existing methods are presented, which demonstrate the usefulness of the present approach
Exploring Two Novel Features for EEG-based Brain-Computer Interfaces: Multifractal Cumulants and Predictive Complexity
In this paper, we introduce two new features for the design of
electroencephalography (EEG) based Brain-Computer Interfaces (BCI): one feature
based on multifractal cumulants, and one feature based on the predictive
complexity of the EEG time series. The multifractal cumulants feature measures
the signal regularity, while the predictive complexity measures the difficulty
to predict the future of the signal based on its past, hence a degree of how
complex it is. We have conducted an evaluation of the performance of these two
novel features on EEG data corresponding to motor-imagery. We also compared
them to the most successful features used in the BCI field, namely the
Band-Power features. We evaluated these three kinds of features and their
combinations on EEG signals from 13 subjects. Results obtained show that our
novel features can lead to BCI designs with improved classification
performance, notably when using and combining the three kinds of feature
(band-power, multifractal cumulants, predictive complexity) together.Comment: Updated with more subjects. Separated out the band-power comparisons
in a companion article after reviewer feedback. Source code and companion
article are available at
http://nicolas.brodu.numerimoire.net/en/recherche/publication
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