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A 4 x 1 element receiving phased antenna array is presented with phase-shifter elements based on injection-locked harmonic self-oscillating mixers. Each phase-shifter element provides the double functionality of variable phase-shifter and down-converter. The phase-shifts applied to the input signals coming from the different antenna patch elements can be selected by dc control signals in a continuous range of 450[degrees]. The required dc control voltages are calculated for the different incident angles by means of harmonic balance simulations. The influences of phase-shift and conversion gain errors on the beam-steering frequency performance of the antenna are studied. Also illustrated is how the phase-shifter parameters can be optimized in order to minimize the frequency scanning. A 4 x 1 element receiving phased antenna array, with an input frequency band centered at 11.25 GHz and the output frequency band centered at 1.5 GHz, has been manufactured for the experimental validation of the simulated results. A beam scanning range from -23[degrees] to 23[degrees] has been experimentally obtained. Index Terms--Beam steering, injection locked oscillators, microwave phase shifters, phased arrays, shaped beam antennas.

A comparison between two well-known near field to far field (NF-FF) transformation methods is presented: the spherical wave expansion (SWE) and the sources reconstruction method (SRM). The goal of this paper is to show the methods performance for NF-FF transformation pointing out the advantages and limitations of each one. First, the computational cost is studied, showing its dependence with the antenna under test (AUT) electric size. Second, the NF-FF transformation accuracy of each method is compared for a fixed AUT electric size, analyzing also the influence of the main parameters that affect the SRM and SWE accuracy. Third, the SRM capabilities are presented, with focus on the NF-NF transformation inside the minimum sphere. Practical applications of the SWE and SRM are illustrated by means of an example of NF-FF transformation and antenna diagnostics problem using measured NF data. Index Terms--Antenna diagnostics, antenna measurement, near field to far field (NF-FF) transformation, sources reconstruction, spherical wave expansion (SWE).

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 'plug-and-play' 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. Index Terms--Electromagnetic interference (EMI), EMI filter, power supply, radiated noise.

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 (3-D) 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 3-D 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. Index Terms--Equivalence principle, equivalent sources, integral equations, inverse radiation problem, near-field far-field transformation (NF-FF).

The support vector regression framework is proposed as the basis for a new antenna array characterization technique able to model radiating structures including all the coupling effects between the elements of the array from experimental data. The obtained model can then be used to solve practical synthesis problems with high accuracy and using an appropriate cost function for template-based specification handling. A design example is presented to show the efficiency of the proposed method. Index Terms--Antenna arrays, antenna pattern synthesis, support vector regression.

A new neural network-based method able to perform synthesis over real radiating structures in presence of obstacles is presented. The method is based on the ability of neural networks to establish a relation between inputs and outputs from a previous training procedure with known sets of pairs input/output. If such sets are obtained using a full-waveform analysis tool, a neural network can estimate the voltages that must be applied to the radiating elements of an array in order to get a desired radiated field distribution, taking into account interactions between elements and the presence of obstacles in a near environment. Index Terms--Antenna arrays, antenna radiation pattern synthesis, neural networks.

A source reconstruction technique from the measured near fields is proposed to obtain a set of equivalent currents that will characterize the forward and backward radiation patterns of an antenna. Once the equivalent sources are determined, the electromagnetic field at any aspect angle and distance from the antenna can be calculated. In this paper, the method is applied to the evaluation of the radiation from commercial antennas at any observation point. The electric field patterns of a DCS base station antenna at 1800 MHz and a horn antenna at 2500 MHz have been calculated and plotted at several distances from the antenna. This method can be used in characterizing the 'reference volumes' or exclusion zones for transmitting antennas dealing with the maximum levels of electromagnetic radiation safe for human exposure, as stated in many national and international regulations. Index Terms--Antenna measurement, equivalent magnetic currents, human exposure, near-field pattern, near-field to far-field transformation, non-ionizing EM fields.

In this paper, a near-field to far-field (NF-FF) transformation for the case of spherical scanning using equivalent magnetic currents (EMCs) and matrix methods is addressed. It is based on the decoupling of the field components and the iterative retrieval of the radial component of the electric field. The technique is applied for far-field calculation as well as for the estimation of the current distribution of the antenna under test (AUT) using spherical near-field facilities. Results from measured near-field data of several antennas are presented and compared to those of the analytical solution via a spherical wave mode expansion method. Index Terms--Equivalent sources, near-field (NF) far-field (FF) transformation.

In this paper, we present a direct optimization procedure that utilizes phaseless electric field data over arbitrary shaped surfaces for the reconstruction of an equivalent magnetic current density that represents the radiating structure or an antenna under test. Once the equivalent magnetic current density is determined, the electric field at any point can be calculated. Numerical results (both simulated and experimental) are presented to illustrate the applicability of this approach for nonplanar near-field to far-field (NF-FF) transformation as well as to antenna diagnostics. The results are presented using both theoretical and experimental phaseless data over one and two planes. Index Terms--Amplitude-only data, near-field far-field transformation, optimization, phaseless synthesis.

Main plane far-field radiation pattern of an antenna under test from the corresponding main plane near-field data, using a circular-line acquisition, is presented. The method is based on the reconstruction of equivalent magnetic currents (EMCs) using decoupled integral equations and one-dimensional source components. The resultant fast procedure is applicable to linear and quasilinear array antennas. Experimental data results and comparison with complete spherical acquisition and center-line acquisition are presented. Index Terms--Antenna measurements, antenna radiation patterns, electric field measurements.