100,329 research outputs found
Wide tuning-range planar filters using lumped-distributed coupled resonators
No full textThis paper describes a discretely tunable filter topology based on lumped-distributed coupled transmission lines, particularly suitable for microelectromechanical systems switching devices. This topology is capable of simultaneous wide-band center frequency and bandwidth tuning, limited only by the electrical size of the transmission lines and the placement density of the switching devices. Low fractional bandwidths can be achieved without the need for large coupled-line spacings due to the antiphase relationship of the lumped capacitive and distributed electromagnetic coupling coefficients. The positions of the additional poles of attenuation due to the lumped capacitive coupling can be selected either above or below band leading to the choice of a narrow bandwidth design having good high-side performance or a design with compromised upper stopband performance, but with no bandwidth tuning limitations. The interaction between a pair of lumped-distributed coupled transmission lines is analyzed and the resulting model is used to develop a filter synthesis procedure. The synthesis procedure and filter performance are validated through theoretical and experimental comparisons using a filter with low-side attenuation poles.This paper describes a discretely tunable filter topology based on lumped-distributed coupled transmission lines, particularly suitable for microelectromechanical systems switching devices. This topology is capable of simultaneous wide-band center frequency and bandwidth tuning, limited only by the electrical size of the transmission lines and the placement density of the switching devices. Low fractional bandwidths can be achieved without the need for large coupled-line spacings due to the antiphase relationship of the lumped capacitive and distributed electromagnetic coupling coefficients. The positions of the additional poles of attenuation due to the lumped capacitive coupling can be selected either above or below band leading to the choice of a narrow bandwidth design having good high-side performance or a design with compromised upper stopband performance, but with no bandwidth tuning limitations. The interaction between a pair of lumped-distributed coupled transmission lines is analyzed and the resulting model is used to develop a filter synthesis procedure. The synthesis procedure and filter performance are validated through theoretical and experimental comparisons using a filter with low-side attenuation poles
A novel mixer linearisation technique using frequency retranslation
No full textThe inherent non-linearity of mixers in communication systems creates numerous undesired effects, which are particularly acute in broadband receiver design for software defined radio (SDR) applications. In this paper, previously investigated mixer linearisation techniques are summarised, and a new technique using frequency retranslation is presented. To the author’s knowledge, this linearisation technique is new. Two-tone-test results show up to 33dB reduction in the distortion products and a π/4-DQPSK modulated carrier yield 22dB suppression of adjacent channel interference (ACI
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Mixer linearisation for software defined radio applications
No full textThe inherent non-linearity of mixers is particularly acute in broadband receiver design for software defined radio (SDR) applications. Here, the receiver frontend ‘sees’ not only the wanted channel, but also a number of nearby signals. A conventional mixer will downconvert all of these received channels to IF, thus adding inband interference to the wanted channel. In this paper, known mixer linearisation schemes are explained and a new technique using frequency retranslation within a linearised mixer architecture is presented. Two-tone-test results from a prototype offered 33dB reduction in the distortion products and 22dB suppression of adjacent channel interference (ACI) for a π/4-DQPSK modulated carrier. A theoretical analysis is also carried out to demonstrate the amplitude and phase matching requirements of the technique
Miniature distributed filters for software re-configurable radio applications
No full textVariable preselection filters will be an important component of any software re-configurable radio design. To be of practical use, such a filter should occupy a minimum of board area in any transceiver layout. Slow-wave filters are introduced and their essential electrical characteristics and miniaturisation advantages are outlined. It is shown that this filter architecture is easily tuneable. MEMS switches can be used to switch line lengths and thus cause the centre frequency of the filter to be altered. MEMS switching is a preferred tuning method because it eliminates the non-linearity introduced by conventional tuning elements. A technique for designing a capacitively loaded, split ring filter is presented and some simulation and measurement results are given. The possibility of pushing the second resonant frequency beyond twice the fundamental frequency is highlighted as a feature of slow-wave filters. This feature is shown to be of limited advantage with the architecture under discussio
A software defined radio receiver test-bed
No full textThis paper identifies the issues that are important in the design of a SDR receiver. Receiver architectures are first discussed, and the conclusion drawn that the conventional superheterodyne structure is most appropriate for a SDR receiver. Issues associated with image rejection, and receiver linearity are discussed. The design of a sweepable preselect filter is discussed in detail. Design considerations for a practical SDR test-bed are presented
Handwritten biographical information on Paulina T. McClung Merritt
No full textA handwritten biography of Paulina T. McClung Merritt by an unknown author, 1892.
Heterogeneous and tissue-specific regulation of effector T cell responses by IFN-gamma during Plasmodium berghei ANKA infection.
No full textIFN-γ and T cells are both required for the development of experimental cerebral malaria during Plasmodium berghei ANKA infection. Surprisingly, however, the role of IFN-γ in shaping the effector CD4(+) and CD8(+) T cell response during this infection has not been examined in detail. To address this, we have compared the effector T cell responses in wild-type and IFN-γ(-/-) mice during P. berghei ANKA infection. The expansion of splenic CD4(+) and CD8(+) T cells during P. berghei ANKA infection was unaffected by the absence of IFN-γ, but the contraction phase of the T cell response was significantly attenuated. Splenic T cell activation and effector function were essentially normal in IFN-γ(-/-) mice; however, the migration to, and accumulation of, effector CD4(+) and CD8(+) T cells in the lung, liver, and brain was altered in IFN-γ(-/-) mice. Interestingly, activation and accumulation of T cells in various nonlymphoid organs was differently affected by lack of IFN-γ, suggesting that IFN-γ influences T cell effector function to varying levels in different anatomical locations. Importantly, control of splenic T cell numbers during P. berghei ANKA infection depended on active IFN-γ-dependent environmental signals--leading to T cell apoptosis--rather than upon intrinsic alterations in T cell programming. To our knowledge, this is the first study to fully investigate the role of IFN-γ in modulating T cell function during P. berghei ANKA infection and reveals that IFN-γ is required for efficient contraction of the pool of activated T cells
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Pelevin’s Trinity in the novel “t”: author – protagonist – reader
No full textThe article attempts to interpret Pelevin's artistic strategy in the novel "T" by exploring its subject organization and addressing the key problems of the author, the protagonist, and the reader as they are seen by the researcher. The article analyzes the peculiarities of constructing the narrative reality in the novel "T", and goes on to discuss Pelevin's philosophic models of the development of the humankind, and the emergence of his new anthropology
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