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A new submillimeter-wave imaging system based on the frequency scanning concept is presented. Using significantly less information than beam-steering techniques, frequency scanning-based imaging systems are able to provide angular information in range-based radar systems which do not allow mechanical or electronic beam steering. Several strategies have been adopted to overcome the low dynamic range due to the propagation losses and non-specular reflection on the object-under-test. Moreover, the system is not only capable of detecting the placement of the objects, but also their profile. In this sense, an imaging application showing the system capabilities for the detection of objects concealed under clothes is presented. Results using 1-D FSAA allowing profile imaging are shown, proving the validity of the proposed system.

A 3-D imaging technique for monostatic radar cross section measurement is presented. The method is based on an existing formulation conceived for bistatic geometries which takes into account the scattered field polarization and is accelerated using the fast multipole method. The synthetic aperture radar (SAR) image processing includes acquired field, which is of interest for polarimetric SAR imaging. In addition, the proposed technique overcomes the limitation of fast-Fourier-transform-based inverse techniques on canonical domains (planar, cylindrical, and spherical). Validation with simulations and measurements is presented. Calculation time is also drastically reduced using graphics processing unit implementation.

The aim of this communication is to present an enhanced phaseless inverse scattering setup and its implementation at the submillimeter-wave band. This setup is based on a modified indirect holography with synthesized reference signal so that a phase shifter is not required. Thus, a phaseless scanner can be built using a simple power detector resulting in a simplified measurement scheme very suitable to work in the millimeter-wave band and beyond. Mechanical phase shifting is used to bypass the use of electrical phase shifters. In addition, the reference signal is injected by coupling the transmitter and receiver antennas so that directional couplers and power combiners are avoided. New errors introduced by these techniques are analyzed and quantified. The method is validated with simulations as well as measurements at 300 GHz.

A scheme for reducing the number of sample points in phaseless acquisition based on Leith-Upatnieks holography is presented. An appropriate choice of the phase of the reference field enables to drastically decrease the sampling rate by acquiring the so-called “reduced” field instead of the real radiated field. The reference phase changes are enabled by applying the recent developments on the synthesis of the reference wave. Moreover, optimal sampling interpolation can be applied to the retrieved field so that the real field can be computed at any point on the acquisition surface. The method is illustrated by means of multiple simulations for observation domains such as straight lines, azimuthal circles as well as for a plane-polar acquisition scheme.

The aim of this paper is the description of experience in teaching a university extension course for manufacturing homemade antennas and receiving weather-satellite images with them. We thus introduce students to the field of antennas with a very entertaining application example that they can easily reproduce by themselves. The different topics covered by the course are described, with a special emphasis on the description of the antennas and how they are manufactured, which are the core topics of the course. Antenna reflection parameters and received weather images are shown to illustrate the good results achieved by the students.

A technique to estimate the attitude of an object using RFID tags is presented in this paper. The approach is based on the application of MUSIC algorithm to the phase measurements of an array of RFID tags attached to the object. The cost and infrastructure of the system is minimized since a single transmitter antenna is required. The performance of this technique was validated through simulations and measurements in an anechoic chamber. Results showed that the estimated attitude accuracy is within the uncertainty margin of the RFID reader employed in wide angular range. In addition, the calibration of the array turns out to be critical in order to reduce errors mainly caused by the difference between the effective separation between RFID tags and its expected value.

A new method recently developed for planar nearfield broadband phaseless antenna measurement is adapted to work with a reduced set of points. The method is an extrapolation of the conventional off-axis holography in which a frequency sweep is made at each point of the acquisition grid, and the phase is retrieved simultaneously for all the frequencies by filtering the hologram in the time-domain. As the phase is retrieved independently at each acquisition point, non redundant sampling techniques can be applied without the need of increasing the spatial bandwidth of the hologram. The bounds of the error in the far field pattern regarding the effect of mechanical errors and noise are studied by means of Monte Carlo simulations. A measurement example in the Ka band is presented to validate the method.

A new efficient method for broadband antenna characterization from phaseless acquisitions in the frequency-domain (FD) is presented. The phase-retrieval technique is based on an extrapolation of the off-axis indirect holography. In common with the conventional approach, the power of the interferometric field of the antenna under test (AUT) and a reference antenna, whose field is known in advance, as well as the power of the AUT alone, is measured at the desired frequencies. Nevertheless, the phase retrieval is accomplished independently at each spatial point by filtering in the time-domain (TD) rather than in the k-space. Thus, the dependency of the phase retrieval on the position accuracy is reduced and it can be accomplished simultaneously at all frequencies without resorting to iterative schemes. Moreover, it yields a less dense sampling and a phase-retrieval algorithm not dependent on the geometry of the acquisition. The method is illustrated with a numerical example in the W-band as well as with two near-field (NF) measurement examples in the Ka- and W-bands, This work was supported in part by the European Science Foundation under the RNP NEWFOCUS programme, in part by the Ministerio de Ciencia e Innovación of Spain/FEDER under Grant MIRIIEMTEC2014-54005-P and Grant TEC2014-55290-JIN, in part by the Gobierno del Principado de Asturias through the PCTI 2013–2017 GRUPIN14-114, in part by Predoctoral Grant BP11-169, in part by the Grant LINE 525-002, and in part by the Academy of Finland through the DYNAMITE project

A phase retrieval technique for multifrequency scattered field acquisition is presented in this paper. The proposed setup is based on indirect holography schemes so that it combines the desired signal with a known reference signal. The setup is used together with a two-dimensional frequency scanning (FS) antenna and, therefore, the positions of scatterers can be retrieved without the need of moving either the antenna or the objects.

The aim of this paper is the development of characteristic basis functions (CBFs) for homogeneous dielectric bodies that are modeled with the surface equivalence principle. This approach contributes to generalize the characteristic basis function method (CBFM) for any kind of material. The foundations for the generation of these new basis functions are widely revised and the CBFM is adapted for this purpose. The validity of the method is illustrated with the systematic analysis of canonical geometries as well as with the computation of the specific absorption rate inside a head-like geometry. In all the cases, the error in the current distribution as well as in the near- and far-field is considered. In addition, a detailed comparison of the generation of the CBFs using plane waves and spherical waves is also carried out.

The analysis as a stationary method of the spatial domain decomposition (SDD) technique with several enhancements is studied in this article. In particular, we consider two of the most popular modifications of the SDD method: (i) extension of the domains and (ii) introduction of a relaxation parameter. Despite both modifications, we show that the method can still be formulated as a stationary method and, therefore, the convergence study can be derived from the iteration matrix. Several examples for three-dimensional geometries are considered to check the validity of the formulation. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2388–2393, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26245

The efficient analysis of multiple problems that only differ on a small portion of the entire geometry is considered in this work. The method-of-moments (MoM) matrix is compressed with the characteristic basis function method in order to reduce its size. Once the matrix related to the common part of the geometry (mother structure) has been computed and compressed, several algebraic manipulations are applied in order to speed up the solution of the final system of equations. Thus, the computation of the total structure, which comprises the mother-structure plus an additional geometric element, can be efficiently accomplished. The method is illustrated with the analysis of an on-board antenna on a helicopter, where multiple positions of the rotor blades are analyzed.

The following paper deals with the problem of computing a safety perimeter, i.e., where the electromagnetic fleld due to a radiating system exceeds a certain electromagnetic value. The ∞exibility of the source reconstruction method (SRM) is employed to compute the flelds almost everywhere around the antenna. Techniques for fast computing of the flelds in the spectral and spatial domains exploiting the characteristics of the SRM are considered in order to avoid expensive integrations over the sources surface. Results for a log- periodic antenna and a base station antenna for cellular phone systems are shown, and compared with the usual far-fleld approximation.

We present a multilevel version to the characteristic basis function method (CBFM). This technique extends the range of applicability of the conventional CBFM and allows a direct solution of problems even when they exceed 250,000 degrees of freedom. In this paper, it is shown how we can use the multilevel CBFM, which is a natural extension of the conventional approach and which saves both time and memory, and yet retains excellent accuracy in the computed far fields. Also, the adaptive cross algorithm is used for fast calculation of the interaction between the blocks in the process of generating the reduced matrix.

Parallel implementation of the multilevel characteristic basis function method is discussed in this article. The use of this method enables us to solve very large electromagnetic problems in a direct manner via a recursive application of the characteristic basis function method. Furthermore, we show that, unlike the iterative schemes, the present method is very well suited for parallelization. Examples are presented to show that upto one million unknown problems can be solved on a workstation using the present scheme, and that the results show very good agreement with those derived by using analytical or fast multipole methods. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2963–2969, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24767

This article presents an acceleration technique for the fast calculation of the impedance matrix elements in the method of moments in the case of using characteristic basis functions (CBFs). This technique is based on taking advantage of the smooth amplitude and phase behaviors of the fields generated by a CBF when the distance is sufficiently large. Computational efficiency is realized by calculating the reaction between a source-CBF and a test-CBF by first evaluating a sampling of the field at a sparse set of points, and then computing the fields at the rest via the use of interpolation. Thus, this procedure avoids the highly expensive integration in the source domain that is needed to calculate the radiated field in the entire test domain when following the conventional procedure. Phase unwrap prior to interpolation and the fast sample calculation scheme are detailed in the article. The technique has been validated by considering several examples involving Radar Cross Section computations. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1818–1824, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24478

The Support Vector theory combined with antenna array modeling based on the Method of Moments is proposed to provide an accurate synthesis method able to solve problems specified in terms of a template or a mask, taking into account all the real properties of the radiating structure and its environment, such as coupling effects or the presence of an obstacle, and without the need of the measurement of training patterns. Illustrative results are presented.

This article presents a technique based on domain decomposition applied to method of moments. Geometry is split in overlapped sections. Radiation due to other sections is considered as excitation to solve every section. This radiation is modeled by equivalent currents situated on surfaces at the beginning and end of every section. The aim of this method is to reduce the computational complexity of method of moments. Several examples with 2D corridors are shown and also some examples of converge failures. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 172–176, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23034

Neural networks and genetic algorithms are combined in a new hybrid technique able to perform synthesis tasks over passive-element antenna arrays, whose radiation pattern is defined by the coupling effects between the active and passive elements. The combination of both methods improves the results obtained using neural networks, also reducing the computation time required by genetic algorithms. Some significant results are presented.

An error characterization tool is presented in this contribution to study the effect of mechanical and positioning errors in the near-field to far-field transformation and the computation of the aperture field processes in different planar measurement setups. Validation of the error simulation tool is made by comparison of the results with a set of measurements in a planar near-field range.

An inverse scattering method based on the Surface Equivalent Principle and the use of Genetic Algorithms is presented in this contribution. This technique is used for the estimation of constitutive parameter of homogenous dielectrics with any permittivity and conductivity. The dielectric under test is illuminated with a set of plane waves at a single frequency, under 2D TM case assumption. The dielectric composition is estimated from the scattered field measured on a circumferential observation domain. Proper Genetic Algorithm tuning as well as inverse problem parameters coding have been tested by means of simulation examples.

A phaseless data acquisition applied on a reduced set of points is presented for inverse scattering problems. The setup is based on the Leith-Upatnieks holography with synthesized reference waves so that the phase of the reference wave can be adjusted to acquire the so-called “reduced field” instead of the regular field. Thus, nonregular sampling techniques can be applied resulting in strong reduction in the number of acquisition points. The technique is validated using simulation and measurement examples at microwave frequencies, This work was supported by the Ministerio de Ciencia e Innovación of Spain/FEDER under Projects TEC2011- 24492 (iScatt), CSD2008-00068 (Terasense), and MICINN-11-IPT-2011-0951-390000 (Tecnigraf), by the European Union Seventh Framework Programme (FP7/2007-2013) under Grant 600849 (INSIDDE)

A measurement setup for profile reconstruction of metallic targets in the 90 GHz frequency band is proposed and tested. Inverse Synthetic Aperture Radar (iSAR) formulation is used to calculate the radar reflectivity from the measured scattered field. This reflectivity gives a spatial image of the Objet Under Test (OUT) which provides information about the profile of the OUT. Measurements are done using a planar measurement setup for mm- and sub-mm frequency bands. Aiming to test the system resolution, a metallic plate with four different size holes has been chosen as OUT. Profile reconstruction results using this measurement setup are shown.

Thus, the reduction of the number of unknowns results very attractive since it reduces the demanded computational resources in terms of memory and CPU time. In the method of moments context, the choice of the basis functions has a strong impact on the degrees of freedom that are required to solve the problem and, therefore, strategies for unknowns re‐ duction are based on choosing the basis functions as good as possible.

The generation of CBFs for dielectric bodies based on illuminating with external waves is considered in this paper. The conventional approaches for perfect electric conductors involve splitting the surface of the body into open pieces which must be solved independently for multiple external waves propagating in the background media. It will be detailed in the paper how these pieces must be handled in the case of dielectric bodies and how the external waves must be chosen. The simulation of a dielectric body with the CBFM is accomplished to validate the method.

A technique for ntenna placement on electrically large structures is presented in this paper. The method of moments matrix is compressed with the characteristic basis function method so that it can be fitted into the available RAM memory. Potential positions of the antenna are handled as duplicated blocks with one version containing the antenna and the other one not. After that, a partial solution of the structure is accomplished so that it can be resumed from a common point in order to save time.

The convergence of modified spatial domain decomposition methods is studied in this paper. In particular, the case of spatial domain decompositions with extended domains is considered. The inclusion of a relaxation parameter to achieve a better convergence in certain cases is also included in the formulation. Several examples are shown to validate the analytic formulation that is presented.

Field retrieval is analyzed in this paper for the case of an antenna measurement distorted by multiple scatterers. This retrieval is carried out by filtering the effect of the obstacles. Two techniques are considered: i) computing the equivalent currents on surfaces enclosing the obstacles and the antenna; ii) computing the spherical wave expansion corresponding to each object.

The Characteristic Basis Function Method (CBFM) [1] has recently been proposed for the generation of a new class of basis functions with very desirable properties, namely the ability to model the currents on an arbitrarily-shaped body with a much smaller number than that needed when employing the traditional low-level basis functions, such as RWGs and rooftops. The CBFs are defined as linear combinations of traditional low-level basis functions and, therefore, the reaction terms associated with the generation of the reduced matrix can be computed through the low-level reaction terms by implementing the matrix products (see [2],[3]) efficiently.

The aim of this paper is to present a method to carry out the synthesis of large phased arrays when they are affected by complex environments which can influence the radiation pattern. The synthesis is performed with the help of the Multilevel Characteristic Basis Function Method to calculate a matrix relating input voltages and the far field pattern samples. The method is illustrated with the synthesis of a Secondary Surveillance Radar antenna on a turret containing multiple obstacles

A new efficient technique for calculating the reaction between characteristics basis functions has been presented. The proposed method enables us to bypass the computation of the off-diagonal of the MoM matrix. For the case of contiguous blocks, an efficient hybrid approach has been developed that combines the conventional MoM matrix approach with the interpolation technique. Numerical results show that the technique is able to speed up the reduced matrix filling time without sacrificing the accuracy of the RCS results.

In this paper, a technique is presented for analysis corridors or similar structures where the field is confined in a limited area. The structure is split into several overlapped domains. Equivalent currents are placed at the beginning and the end of the overlapped sections to model the radiation of the previous and next section. Several results are shown to show the convergence of the method. (5 pages)

The aim of this study is to present a technique for object geometry retrieval using scattered field information based on phaseless acquisition, so that a scanning system can be implemented without the need of an expensive vector network analyser. The inverse scattering is accomplished through a two-step strategy that is powered thanks to the combination of the scattered signal with a synthesised reference wave. Thus, the phase is firstly recovered by considering the spectral properties of the mixed signal. Secondly, the reflectivity of the object is computed by means of an inverse scattering algorithm accelerated by a multipolar expansion. The technique is applied and validated for planar as well as spherical ranges considering simulated as well as measured data.

A novel scheme for planar near-field phaseless antenna measurement based on off-axis holography is presented. Separation of the image terms of the hologram is artificially increased by multiplexing the measurements of two sub-sampled holograms generated with two 180° phase-shifted reference waves. Combination of both sub-sampled holograms produces replicas of the image terms at half a period distance of the originals in the spectral domain, while the amplitude of the original image terms is highly reduced, easing the filtering process of the desired replica. The higher separation of the image terms reduces overlapping making the method suitable also for the characterization of medium and low gain antennas in the near-field. As the separation is artificially increased, the reference antenna can be placed close to the antenna under test allowing to reduce the scan distance and the sensitivity to scan axis errors. Nevertheless, spatial multiplexing requires the retrieved data to be spatially low-pass filtered to remove the effect of the aliasing. Mirror reflection is used for illuminating the acquisition plane with the reference wave, being the phase shift achieved by means of a mechanical displacement of the mirror. The effect of the location of the reference antenna on the position and shape of the image terms and their replicas has been studied through numerical simulations for a setup in the W-band. Experimental validation of the method is presented for the characterization of three different antennas at 94 GHz.

The development of Low-Earth-Orbit (LEO) satellite communications aims at delivering low-cost worldwide internet connection. The development of compact and low-cost user terminals on Earth represents a fundamental step to reach the consumer mass-market. Here, we present the design, fabrication and test of a 3D-printed 2x2 double-ridged waveguide (DRWG) antenna array with waveguide feeding network, working at Ku- Band (10.75 – 14.5 GHz) with simulated total efficiency $\gt 70$%. A 4x4 array is also designed leveraging the previous concept with simulated total efficiency $\gt 60$% and realized gain of $\sim 16$ dBi, paving the way for innovative low-cost antenna solutions for user’s terminal.

The application of Artificial Intelligence described in this article is intended to resolve the issue of speculation on the stock market. Genetic Algorithms is the technique that is used, with the article focusing on the different ways that chromosomes can be designed and on how the pertinent evaluation mechanism is established. The problem will be based on the speculation systems that are typical of Technical Analysis.