1,721,169 research outputs found
A Method to Detect Subsurface Targets by Under-sampled Multifrequency Data
No full textImaging buried objects embedded within electrically large investigation domains can require a large amount of measurement points. Thus, the need to reduce the number of spatial measurement points arises. Here, a method for detecting and localising shallowly buried scattering targets from under-sampled multifrequency far-zone data is proposed and checked by numerical examples
Unequally excited generalised random binned antenna arrays
No full textIt has been recently shown that random arrays paired with a proper excitation strategy can be used to shape the array factor. These random arrays were termed unequally excited totally random arrays (TRAs). This scheme allows to greatly enlarge the class of obtainable patterns, well beyond the classical single beam. However, its main disadvantage is a reduction of the achievable performance, the latter measured in terms of the deviation from the average array factor. In this contribution, a strategy for remedying (even only partially) to such a loss of performance by retaining the same flexibility in shaping the pattern is addressed. To this end, a new scheme for generating random arrays that merges unequal excitations and a suitable generalised binned procedure is introduced. It is shown that this new model of generalised binned arrays always outperforms unequally excited TRAs. In particular, the study is focused on symmetric arrays (for which the elements are deployed symmetrically with respect to the array aperture centre) which allows to get closed-form expressions without invoking some common assumptions that in general do not hold true in practice. The theoretical findings are assessed by several numerical examples for the case of multi-beam array factors
RCS Estimation by Single Frequency Near-field Data
No full textRadar Cross Section (RCS) is a far-field quantity that describes the scattering ability of a target across the different directions. Nonetheless, for a number of reasons, it is convenient to use near-field data for RCS estimation. In this contribution, an imaging based method for monostatic RCS estimation is considered. In particular, a comparison between single-frequency and multi-frequency near-field data is presented
Spatial and frequency measurement optimization in Subsurface Imaging
No full textThis paper deals with microwave subsurface imaging for a multi-monostatic/multi-frequency configuration. The focus is on devising a suitable data sampling scheme that requires as low as possible data but preserves the achievable performance. To this end, we introduce two sampling schemes. The first one is based on analytical arguments subtended by the recently introduced warping approach. The second sampling method relies on a sensor selection procedure called maximal projection onto the minimum eigenspace. The two approaches are compared for different configuration parameters, and both show a dramatic data reduction as compared to sampling schemes commonly employed in literatur
Incoherent Migration for Near-Field Imaging by Uncharaterized Antennas
No full textIn this paper we present an incoherent migration (IM) algorithm for near-field reconstructions and without knowing the antenna's response. An analytical study is presented to compare the achievable performance by IM against its coherent counterpart. Numerical examples employing two different type of antennas whose responses are not accounted for in the reconstruction process show that IM does not suffer from antenna uncertainties
Phase-Only Excited Random Antenna Arrays
No full textUsually random arrays have uniform amplitudes along the aperture and only contemplate a linear phase shift between antenna elements. In this paper, we show, through some numerical results, that it is possible to obtain great flexibility on the radiation pattern by exploiting the potential of phase-only excited random arrays. Indeed, when the phase-tapering along the array aperture is nonlinear, it is possible to obtain radiation patterns with characteristics that can not be obtained with conventional equally-excited random arrays
Slot Antennas for Microwave Brain Imaging by Accounting the Role of Hair
No full textIn this contribution, we describe and validate slot antennas for microwave brain imaging. The antenna consists of a slot enclosed within a cylindrical brick containing coupling liquid medium. Numerical examples and experiments on a few real human heads show that the proposed antenna exhibits S11 below -10 dB over the selected frequency band [1], [2] GHz
A greedy approach for reducing data in near-field measurements
No full textIn this paper, a sampling strategy which allows to take advantage of all a priori information available on the Antenna under test in reducing the measurement number is proposed. Experimental results show that the required sampling points returned by the proposed method are lower than the ones needed by the standard warping and half-wavelength sampling
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