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More and more people are turning to narrowband imaging as a strategy to combat light pollution and moonlight. The traditional method for utilising narrowband filters is to use a set of individual filters and a monochrome camera to...
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More and more people are turning to narrowband imaging as a strategy to combat light pollution and moonlight. The traditional method for utilising narrowband filters is to use a set of individual filters and a monochrome camera to capture a series of subs for each filter. These are then stacked and combined to produce a colour image. New filters are now being marketed that pass light at multiple emission wavelengths. For example, the STC Duo filter passes hydrogen-alpha and oxygen-Ill simultaneously, while the OPT Triad filter passes hydrogen-alpha, oxygen-Ill and hydrogen-beta simultaneously. The idea is to use these filters with a colour camera, such as a DSLR or a one-shot-colour astro-camera, to capture emission wavelengths simultaneously without the need for multiple individual filters or a filter-wheel.
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A new model for accurate calculation of the coupling coefficient between two degenerate modes (in dual-mode filters) or two resonators in standard filters is presented, validated, and compared with the standard model through simul...
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A new model for accurate calculation of the coupling coefficient between two degenerate modes (in dual-mode filters) or two resonators in standard filters is presented, validated, and compared with the standard model through simulation and test. New filter geometries are devised and investigated in order to improve the narrowband performance. Smaller resonator separation is achieved by moving the portions with current peaks in adjacent resonators away from the coupling region and hence bringing the resonators closer. This is a crucial issue for compactness. Two new microstrip filters with FBW values of 0.02% and 0.14% are demonstrated and compared with two others previously reported using this notion.
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The paper presents a new theory of coupled resonator bandpass microwave filters of arbitrary bandwidth. Constraints on the scattering parameters of lossless, time-invariant, and reciprocal two-port networks, expressed as rational ...
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The paper presents a new theory of coupled resonator bandpass microwave filters of arbitrary bandwidth. Constraints on the scattering parameters of lossless, time-invariant, and reciprocal two-port networks, expressed as rational functions of the physical frequency, are presented. Filtering functions exhibiting arbitrarily positioned transmission zeros and locally symmetric or asymmetric responses with respect to the center of the passband, and satisfying these constraints are then introduced. A direct synthesis technique to extract the elements of the transversal equivalent circuit to yield a prescribed response is presented. Response-preserving similarity transformations are then applied to the circuit to force a desired topology. As opposed to the prevailing narrowband approximation, any topology other than the transversal will have off-diagonal elements that depend on frequency. Interesting features that are not found in the narrowband approximation are reported. Examples demonstrating the soundness of the theory are presented.
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This paper presents a simple feedback methodology that uses second order filters to control narrowband resonant and non-resonant vibration of a structural system. In particular, a single degree-of-freedom system is studied through...
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This paper presents a simple feedback methodology that uses second order filters to control narrowband resonant and non-resonant vibration of a structural system. In particular, a single degree-of-freedom system is studied throughout the paper. The idea of the methodology is based on the fact that direct feedback is effective for in-phase vibration control. Thus, the position, velocity and acceleration are respectively fed back to control the low, resonant and high frequency vibration of the system. Each of these is passed through a band pass filter of second order that is inserted to extract and feed back the in-phase signal component only. This is called narrowband feedback. It is demonstrated with experiments that narrowband feedback is useful for narrowband control of resonant and non-resonant vibration.
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The transmission characteristics for Rb-85 and Rb-87 laser-induced dichroism atomic filters operating on rubidium D-1 lines (795 nm) transitions are analyzed. By means of semiclassical density matrix equations of motion, a three-l...
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The transmission characteristics for Rb-85 and Rb-87 laser-induced dichroism atomic filters operating on rubidium D-1 lines (795 nm) transitions are analyzed. By means of semiclassical density matrix equations of motion, a three-level model for the transmission characteristics of the ground state laser-induced dichroism atomic filter is presented. Calculative results show that this filter, using two counterpropagating pump and probe beams, can obtain higher transmission, narrower bandwidth and larger tuning capability than that using two copropagating pump and probe beams; with the aid of counterpropagating pump, the Rb-85 ground state laser-induced dichroism atomic filter can be more effective to achieve higher peak transmission (>34%) and larger tunability (>1 GHz) than the Rb-87 ground state laser-induced dichroism atomic filter in the same operation parameters. This result may be helpful for improving peak transmission (14.6%) of Rb ground state laser-induced dichroism atomic filter reported (CERE A. et al., Opt. Lett. 34(7), 2009, pp. 1012-1014).
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In this paper, a surface-mounted dielectric resonator-based balanced bandpass filter is proposed. By utilizing the TE01 delta mode as a dominant mode of the cylindrical dielectric resonator, it can be excited in differential mode ...
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In this paper, a surface-mounted dielectric resonator-based balanced bandpass filter is proposed. By utilizing the TE01 delta mode as a dominant mode of the cylindrical dielectric resonator, it can be excited in differential mode to achieve good common-mode suppression in differential filter passband. To validate the design idea, a second-order balanced narrowband bandpass filter with center frequency at 5.53 GHz has been designed, fabricated, and measured. The design parameters of the proposed filter are: insertion loss 0.2, 3 dB Bandwidth (BW) 67.1 MHz, and return loss 23 dB, and common-mode separation is more than 30 dB. There is good agreement between the simulated and measured results.
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The design and fabrication of a high temperature super-conducting stripline filter for high power application are presented. The measured results showed the filter had a 0.78% bandwidth at 2090 MHz. The input power increases to 36...
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The design and fabrication of a high temperature super-conducting stripline filter for high power application are presented. The measured results showed the filter had a 0.78% bandwidth at 2090 MHz. The input power increases to 36 dBm without evident change in insertion loss.
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We often encounter a situation where several half-duplex based narrow-band interferes give much damage to DS-CDMA signal with sudden changes in the power level. In this paper, we discuss a method to reject such narrow-band interfe...
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We often encounter a situation where several half-duplex based narrow-band interferes give much damage to DS-CDMA signal with sudden changes in the power level. In this paper, we discuss a method to reject such narrow-band interference in DS-CDMA system. We propose an adaptive digital filter-based narrow-band interference canceler with an interference detection method. We show the rejection and detection performance obtained from computer simulation.
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We often encounter a situation where several half-duplex based narrow-band interferes give much damage to DS-CDMA signal with sudden changes in the power level. In this paper, we discuss a method to reject such narrow-band interfe...
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We often encounter a situation where several half-duplex based narrow-band interferes give much damage to DS-CDMA signal with sudden changes in the power level. In this paper, we discuss a method to reject such narrow-band interference in DS-CDMA system. We propose an adaptive digital filter-based narrow-band interference canceler with an interference detection method. We show the rejection and detection performance obtained from computer simulation.
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Mechanical noise is usually a mixture of narrowband and impulsive noise which needs complex active noise control (ANC) algorithms to improve the de-noising performance. But the ANC algorithm with a high computation load will reduc...
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Mechanical noise is usually a mixture of narrowband and impulsive noise which needs complex active noise control (ANC) algorithms to improve the de-noising performance. But the ANC algorithm with a high computation load will reduce the real-time performance of an ANC system, thus decreasing the attenuation performance and even leading to divergence. To alleviate this contradiction in narrowband ANC systems, a new virtual filtered-x L0 norm discrete Fourier cancellation (FxL0DFC) based hybrid FxNLMS(filtered-x normalized least mean square)-FxDFC framework is proposed to decrease the total computing load and keep good attenuation performance. For a fast-changing noise, the FxNLMS algorithm is employed. The new virtual FxL0DFC algorithm serves to prepare parameters for steady-state, and when this happens, the FxDFC algorithm with the parameters provided by FxL0DFC is applied. Compared to using the FxNLMS algorithm to attenuate narrowband periodical noise, the FxDFC algorithm has nearly the same tracking performance while having a low computational load. As a result, the FxL0DFC-based FxNLMS-FxDFC algorithm leads to a reduction of the total computational load. Moreover, the proposed method performs excellently in terms of tracking in simulations and experiments on actual data, particularly in environments with rapid power changes and impulsive noise.
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