Spatial filter

About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.

Beamforming and imaging with the BYU/NRAO L-band 19-element phased array feed

Abstract: An experimental 19-element L-band phased array feed was installed on the Green Bank 20-Meter Telescope in October 2007 and July 2008 to measure sensitivity and effciency and demonstrate signal processing algorithms for array calibration, multiple beam formation, imaging, and adaptive spatial filtering methods for interference mitigation. System noise performance was characterized using a warm absorber/cold sky Y-factor setup. The peak beam aperture effciency was 69% and the minimum beam equivalent system temperature was 66K. With a single reflector pointing, a high sensitivity image of a field of view approximately two half-power beamwidths in diameter can be produced. Measured figures of merit compare well to numerical simulations, indicating that complicating effects such as mutual coupling are understood well enough to enable the next phase of array feed development to proceed on firm grounds.

On the effect of diffraction on traveltime measurements

Abstract: SUMMARY All observed waves are of finite frequency and are sensitive to a finite volume of the medium through which they pass. Diffraction causes a loss of information about time contained in the initial front of a wavefield (often referred to as wavefront healing). This effect depends upon frequency and propagation distance and imposes a low-pass filter on the spatial resolution of time measurements. A sequence of canonical, numerical experiments that simulate the diffraction of a perturbed plane wave at a fixed distance is described. Traveltimes are measured using a variety of techniques on a range of waveforms. It is empirically verified that a single Fresnel zone describes the spatial filtering effect of the propagation of a broad-band wavefield, even in the regime where the initial time perturbation cannot be represented by a linear perturbation term. For narrow-band wavefields, more Fresnel zones come into play as the bandwidth is reduced. Measurements of time include a component of signal-generated noise coherent over a small scale which scales with the Fresnel zone. It is found that, for traveltimes measured by automated picking, the width of the Fresnel zone is described by a time delay of (&I< T/4 (here T is one period). On the other hand, the width of the Fresnel zone for traveltimes measured by correlation is wider, characterized by a time delay of ldtl < T/4.

Inspection method and inspection apparatus

Abstract: The present invention provides an inspection apparatus and inspection method The inspection apparatus includes a stage mechanism for supporting an object under inspection A spatial filter is provided in the detection optical system to inspect the object A printer is used to print the results of the spatial filter The spatial filter can be provided in the form of a Fourier transformed image

Array signal processing for radio astronomy

Abstract: Radio astronomy forms an interesting application area for array signal processing techniques. Current synthesis imaging telescopes consist of a small number of identical dishes, which track a fixed patch in the sky and produce estimates of the time-varying spatial covariance matrix. The observations sometimes are distorted by interference, e.g., from radio, TV, radar or satellite transmissions. We describe some of the tools that array signal processing offers to filter out the interference, based on eigenvalue decompositions and factor analysis, which is a more general technique applicable to partially calibrated arrays. We consider detection of interference, spatial filtering techniques using projections, and discuss how a reference antenna pointed at the interferer can improve the performance. We also consider image formation and its relation to beamforming.

Coherence characteristics of electrically excited tandem organic light-emitting diodes

Abstract: A tandem organic light-emitting diode structure, excited electrically in the pulsed domain and confined within a double spatial filter configuration, is observed to emit a low-divergence beam (Δθ≈2.53 mrad, or ∼1.1 times the diffraction limit) with a near-Gaussian spatial distribution. The emission originates from the laser dye Coumarin 545 T, which is used as a dopant. Spectral coherence was determined by use of a double-slit interferometer. The interferometric distribution from our device approximates the interferometric pattern obtained from well-known lasers emitting at λ≈540 nm.