376 research outputs found
Optimizing Antenna Arrays for Spatial Multiplexing: Towards 6G Systems
In this paper we discuss the design of antenna arrays to be used for multiplexing applications. In particular, we introduce a suitable performance index to analyze the effect of the antenna geometry and the distribution of users for the overall performance of Multi-User Multiple Input Multiple Output systems. By means of such performance index, antenna arrays can be designed so as to increase the number of multiplexed parallel sub-channels. Numerical results show that a proper design could allow to double the contemporary served users and the overall system throughput
Radar array diagnosis from undersampled data using a compressed sensing/sparse recovery technique
A Compressed Sensing/Sparse Recovery approach is adopted in this paper for the accurate diagnosis of fault array elements from undersampled data. Experimental validations on a slotted waveguide test array are discussed to demonstrate the effectiveness of the proposed procedure in the failures retrieval from a small set of measurements with respect to the number of radiating elements. Due to the sparsity feature of the proposed formulation, the method is particularly appealing for the diagnostics of large arrays, typically adopted for radar applications
The imaging properties of the Gas Pixel Detector as a focal plane polarimeter
X-rays are particularly suited to probe the physics of extreme objects.
However, despite the enormous improvements of X-ray Astronomy in imaging,
spectroscopy and timing, polarimetry remains largely unexplored. We propose the
photoelectric polarimeter Gas Pixel Detector (GPD) as an instrument candidate
to fill the gap of more than thirty years of lack of measurements. The GPD, in
the focus of a telescope, will increase the sensitivity of orders of magnitude.
Moreover, since it can measure the energy, the position, the arrival time and
the polarization angle of every single photon, allows to perform polarimetry of
subsets of data singled out from the spectrum, the light curve or the image of
source. The GPD has an intrinsic very fine imaging capability and in this work
we report on the calibration campaign carried out in 2012 at the PANTER X-ray
test facility of the Max-Planck-Institut f\"ur extraterrestrische Physik of
Garching (Germany) in which, for the first time, we coupled it to a JET-X
optics module with a focal length of 3.5 m and an angular resolution of 18
arcsec at 4.5 keV. This configuration was proposed in 2012 aboard the X-ray
Imaging Polarimetry Explorer (XIPE) in response to the ESA call for a small
mission. We derived the imaging and polarimetric performance for extended
sources like Pulsar Wind Nebulae and Supernova Remnants as case studies for the
XIPE configuration, discussing also possible improvements by coupling the
detector with advanced optics, having finer angular resolution and larger
effective area, to study with more details extended objects.Comment: Accepted for publication in The Astrophysical Journal Supplemen
IXPE Mission System Concept and Development Status
The Goal of the Imaging X-Ray Polarimetry Explorer (IXPE) Mi SMEX), is to expand understanding of high-energy astrophysical processes and sources, in support of NASAs first science objective in Astrophysics: Discover how the universe works. IXPE, an international collaboration, will conduct X-ray imaging polarimetry for multiple categories of cosmic X-ray sources such as neutron stars, stellar-mass black holes, supernova remnants and active galactic nuclei. The Observatory uses a single science operational mode capturing the X-ray data from the targets. The IXPE Observatory consists of spacecraft and payload modules built up in parallel to form the Observatory during system integration and test. The payload includes three X-ray telescopes each consisting of a polarization-sensitive, gas pixel X-ray detector, paired with its corresponding grazing incidence mirror module assembly (MMA). A deployable boom provides the correct separation (focal length) between the detector units (DU) and MMAs. These payload elements are supported by the IXPE spacecraft which is derived from the BCP-small spacecraft architecture. This paper summarizes the IXPE mission science objectives, updates the Observatory implementation concept including the payload and spacecraft ts and summarizes the mission status since last years conference
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