E. Nova

Radiometric and Spatial Resolution Constraints in Millimeter-Wave Close-Range Passive Screener Systems

This paper presents a comparative study of the radiometric sensitivity and spatial resolution of three near-field (NF) passive screener systems: real aperture, 1-D synthetic aperture (SA), and 2-D SA radiometers are compared. The analytical expressions for the radiometric resolution, the number of required antennas, and the number of pixels in the image are derived taking into account the distortion produced by the NF geometry at nonboresight directions where the distortion is dominant. Based on the theoretical results, a performance comparison among the studied systems is carried out to show the advantages and drawbacks when using the radiometers in a close-range screening application. Moreover, the screener performance in a close-range environment is discussed from the results obtained in the aforementioned comparison.

Optical Signal Processor for Millimeter-Wave Interferometric Radiometry

In interferometric radiometry, the correlations between all pairs of radio-frequency (RF) receivers must be performed in order to obtain the scene visibilities. This represents a cumbersome problem in passive imaging where large signal bandwidths are typically required to achieve fast-acquisition times and improve the radiometric resolution of the image. In this case, the signal distribution and the correlation at intermediate frequencies require very fast signal acquisition and processing subsystems. This paper presents a technique to perform correlations of millimeter-wave signals produced by thermal emission in the optical domain as a solution to the aforementioned problem. The proposed method is based on converting the RF signal to the optical domain by modulating a laser beam with the RF signal using a LiNbO3 phase modulator. This conversion allows to perform the signal distribution in the optical domain to obtain the combination of the receiver pairs. The correlation is obtained by measuring the power of the photocurrent produced by photodetecting the combined signal. The results of an experimental validation consisting on the acquisition of passive images using a linear interferometric array are presented to support the feasibility of the method. In addition, performance considerations of the system have been developed and validated by calculating the standard deviation of a visibility measurement.

Combined passive and active millimeter-wave imaging system for concealed objects detection

In this paper, a comparison between both imaging techniques is performed with the aim of integrating both in a single imaging system. It is expected that the combination of the coherent and incoherent radiation in active and passive operation will offer improved detection and identification of concealed objects. An interferometric radiometer and an active mills-cross have been studied as near field imaging systems. The main parameters have been simulated to foresee their performance as image scanning systems. Moreover, a T-shape active imaging system has been built and measurements have been done in order to test and assess the performance of this imaging geometry.

Characterization of a 94 GHz radiometric imager with mechanical beam-scanning

This paper presents the characterization in terms of spatial resolution and radiometric sensitivity of a W-band Total Power Radiometer (TPR). The TPR is based on a heterodyne receiver with 64 dB of gain and 6.5 dB of noise figure. An antenna system consisting on a pan-tilt scanner has been designed and built in order to aim a 100 mm offset parabolic reflector. With this system, relative temperature images of targets at a 1 m standoff range are obtained in indoor environments with an spatial resolution of 4 cm.

Micrometric deformation imaging at W-Band

The measurement of scattered signals at W Band can be exploited to form images of small deformations with precisions in the order of tenths of micrometers. In this paper an Interferometric Synthetic Aperture Radar setup is proposed to form high resolution reflectivity images and deformation maps of dielectric or metallic surfaces. First, the system geometry of observation based on a linear motion of the radar antennas is described. A CW frequency domain measurement provides the wide band required for high resolution imaging. The scattered field data is focused on the surface spatial domain using a combination of range compression based on Inverse Fourier Transform combined with a backprojection algorithm to form the synthetic aperture with a high cross range resolution. The focusing performance has been assessed by numerical simulations and experimental measurements of simple scattering objects like spheres and trihedrals. Interferometric images of controlled displacements have been obtained showing a good agreement between real and measured displacements. A representative surface deformation test has been also carried out using a metallic rough surface. The interferometric phase difference between acquisitions can be used to image local deformations in the order of tens of micrometers from a range of several meters. Likewise the interferogram coherence shows the degree of decorrelation of the radar reflectivity which provides valuable information for surface random change assessment.

Retina design for 100GHz MST imaging system

A near field imaging system for THz tomographic imaging based on a MST retina (an array of real antennas) has been designed. The main advantage of this implementation is the absence of microwave transmission line distribution networks and the capability to perform high speed imaging. The aim of this paper is to describe the design of the retina in order to maximize the performance of this imaging system.