Yuri Alvarez

Reconstruction of Equivalent Currents Distribution Over Arbitrary Three-Dimensional Surfaces Based on Integral Equation Algorithms

A technique for the determination of the equivalent currents distribution from a known radiated field is described. This Inverse Radiation Problem is solved through an Integral Equation algorithm that allows the characterization of antennas of complex geometry both for near field to far field (NF-FF) transformation purposes as well as for diagnostic tasks. The algorithm is based on the representation of the radiating structure by means of a set of equivalent currents over a three-dimensional (3D) surface that can be fitted to the arbitrary geometry of the antenna. The innovative formulation uses an integral equation involving the electric field due to the currents tangential components to the represented antenna 3D surface. For that purpose, both the magnetic and electric equivalent currents are considered in the integral equations. Regularization techniques are also introduced to improve the convergence of the proposed iterative solution. The paper concludes with several results related to the practical verification of the Equivalence Principle and the characterization of a horn antenna.

94 GHz Dual-Reflector Antenna With Reflectarray Subreflector

The design, construction and measured performance is described of an offset parabolic reflector antenna which employs a reflectarray subreflector to tilt the focused beam from the boresight direction at 94 GHz. An analysis technique based on the method of moments (MoM) is used to design the dual-reflector antenna. Numerical simulations were employed to demonstrate that the high gain pattern of the antenna can be tilted to a predetermined angle by introducing a progressive phase shift across the aperture of the reflectarray. Experimental validation of the approach was made by constructing a 28 times 28 element patch reflectarray which was designed to deflect the beam 5deg from the boresight direction in the azimuth plane. The array was printed on a 115 mum thick metal backed quartz wafer and the radiation patterns of the dual reflector antenna were measured from 92.6-95.5 GHz. The experimental results are used to validate the analysis technique by comparing the radiation patterns and the reduction in the peak gain due to beam deflection from the boresight direction. Moreover the results demonstrate that this design concept can be developed further to create an electronically scanned dual reflector antenna by using a tunable reflectarray subreflector.

EMI Radiated Noise Measurement System Using the Source Reconstruction Technique

One of the requirements that electronics circuits must satisfy comprises conducted and irradiated noise specifications. Whereas conducted noise is well covered in the literature, radiated noise is not. Radiated noise regulations impose limits on the noise measured 3 or 10 m away from electronic equipment. These measurements are usually made in anechoic rooms, which are very expensive. Moreover, the measurement procedure is not a ldquoplug-and-playrdquo feature, but requires a strict measuring protocol. Once the electronic circuit has been tested, the designer remains ignorant of the source of the problem should the regulation not be met. Hence, the procedure to make an electronic circuit comply with regulations is usually one of trial-and-error, in which the experience of the designer is essential. A new radiated noise measurement technique is proposed in this paper with a twofold objective: to simplify the measurement procedure and to obtain more information about noise sources. The main idea is to scan the electric/magnetic field at two arbitrary although known distances. From these measurements, the source reconstruction technique enables the identification of the noise sources in the surface of the circuit and the field estimation at any distance and the assessment of compliance with regulations. Moreover, if regulations are not met, the effect of modifying the noise source can be tested in order to ascertain how the circuit should be modified to comply with regulations.

3D Whole Body Imaging for Detecting Explosive-Related Threats

In this work, a whole-body imaging system for concealed objects detection using a mm-wave radar is presented. 3D high resolution images are generated using a two step process. Initially, an inverse source-based Fast Multipole Method (iFMM) provides a first approximation to the true human torso. Afterwards, the retrieved geometry is refined using the Iterative Field Matrix (IFM) technique. Assuming smooth variations of the human body profile, the object detection is performed by comparing the retrieved surface with a smoothed one. Results are based on Physical Optics simulations of the human body, considering both cases with and without objects.

Novel Broadband Artificial Magnetic Conductor With Hexagonal Unit Cell

The characteristics of a novel broadband artificial magnetic conductor (AMC) design based on a unilayer FSS with hexagonal unit cells and without via-holes are presented by means of FEM simulations and measurements in an anechoic chamber. A comparison between this novel design and other well-known designs is carried out in terms of AMC operation bandwidth. The designed structure shows polarization-angle independence, and its angular stability under oblique incidence is also analyzed based on measurements.

An Inverse Fast Multipole Method for Imaging Applications

An inverse fast multipole method (FMM) for imaging applications is presented. The goal is the acceleration of an inverse source-based method for geometry reconstruction achieved by taking advantage of the multipole expansion properties of the scattered fields and reconstructed equivalent currents. By conjugating the FMM terms, it is possible to recover the equivalent currents from the scattered fields in just one step rather than using matrix inversion or cost function minimization. For the sake of simplicity, 2-D problems where the objects under test having symmetry along one dimension are considered.

Planar Artificial Magnetic Conductor: Design and Characterization Setup in the RFID SHF Band

A novel design of planar Artificial Magnetic Conductor (AMC) based on a Frequency Selective Surface (FSS) for frequencies in the SHF RFID band is presented. A discussion about design parameters and the influence of dielectric substrate thickness on the operating band and on the bandwidth is analyzed. The designed AMC shows polarization angle independency. Its angular margin when operating under oblique incidence is also tested. The discussion is supported by a FEM simulation and measurements in anechoic chamber of the manufactured prototype, with a good agreement between simulations and measurements.

On the Use of the Source Reconstruction Method for Estimating Radiated EMI in Electronic Circuits

Electromagnetic interference (EMI) regulations are a very important issue in the design of almost any electronic circuit. Over the years, “cut-and-try” procedures have been adopted by electronic designers to make circuits comply with these regulations, mainly due to the lack of reliable theoretical models of radiated noise and clear design rules. To gain new insight into this field, a novel approach is presented in this paper based on a well-known technique in the field of antenna design, i.e., the source reconstruction method (SRM). Its application allows a set of equivalent currents to be obtained that behave exactly like the circuit under consideration with regard to radiated noise. From these currents, magnetic and electric radiated fields can be obtained at any point in space, even at 3 or 10 m away from the circuit where the regulations must be met. Moreover, the equivalent currents accurately represent noise sources in the circuit, thus permitting the elements responsible for generating radiated noise to be located. The aforementioned method would enable designers to reduce the use of anechoic-chamber facilities when testing their designs, thereby leaving the chamber only for final certification purposes.

Sparse Array Optimization Using Simulated Annealing and Compressed Sensing for Near-Field Millimeter Wave Imaging

The optimization and use of a sparse array configuration for an active three dimensional (3D) millimeter wave imaging system for personnel security screening is presented in this work. The combination of the optimization procedure with the use of Compressed Sensing techniques allows drastic reduction in the number of sensors, thereby simplifying the system design and fabrication and reducing its cost. Representative simulation results showing good performance of the proposed system are provided and supported by sample measurements.

Novel Bow-tie–AMC Combination for 5.8-GHz RFID Tags Usable With Metallic Objects

A novel combination of coplanar waveguide (CPW)-fed double bow-tie slot antenna and artificial magnetic conductor (AMC), which meets the requirements of a 5.8-GHz SHF RFID tag antenna usable on metallic objects, is presented. The manufactured prototype is characterized in terms of return loss, gain, and radiation pattern measurements in an anechoic chamber, both alone and on a metallic plate.