J. L. Araque Quijano

Equivalent current approach as an advanced field interpolation technique

This paper presents an investigation of a new technique for the accurate determination of the full sphere pattern of an antenna from truncated spherical near field measurements. The approach was first described and is based on determining a set of equivalent currents that radiate the same pattern in the known area and thus extrapolate the unknown fields in the truncated area. The study is performed on actual measured near-field data to investigate the effectiveness of the technique in realistic spherical near field antenna measurement scenarios.

Antenna placement based on accurate measured source representation and numerical tools

Accurate electromagnetic models of measured antennas are available from the expansion of the measured field using equivalent currents. The constructed model is importable in commercial Computational Electromagnetic (CEM) solvers in the form of a Huygens Box. In flush-mounted antenna applications, the measurement of the antenna sited in a locally relevant scenario and subsequent data processing require special attention. This paper, discuss details of the appropriate characterization of the source antenna for numerical computation in flush mounted scenarios. Post processing features and successive link to commercial CEM solvers are covered. The achieved accuracy of the measured source representation is investigated by comparing to full wave simulation.

Application of evolutionary algorithms in the design of compact multi-band antennas

This paper presents an application of a novel design approach, which combines genetic algorithm, local optimization and frequency reconfigurability. The adopted case study is a quad-band antenna for vehicular GSM/DCS/PCS communications; focus has been put on designing an antenna with good return loss and feasible geometry. The reliability of the performances of the output structure over the whole frequency bands have been checked by use of dedicated simulations. Overall, the designed antenna shows very good return loss over the bands of interest.

Application of the Dual-Equation Equivalent-Current Reconstruction to Electrically Large Structures by Fast Multipole Method Enhancement [AMTA Corner]

A number of interesting applications of the equivalent-current/source method (EQC) have recently been presented for antenna design and diagnostics. The Dual-Equation formulation has been proven to be superior in terms of accurately reconstructing sources on, or very near, the AUT structure, and is the only formulation directly applicable for diagnostics [1]. The maximum antenna size that can be handled by this method is limited by memory and running time constraints, due to the construction and solution of the linear system describing the problem. This paper reports the enhancement of the Dual-Equation formulation by the integration of the Fast Multipole Method, which allows dealing efficiently with large antennas.

Innovative representation of antenna measured sources for numerical simulations

Placement analysis in complex antenna scenarios require accurate computational electromagnetic (CEM) tools. A fundamental requirement to achieve truthful results, is that the source antenna must be accurately modelled. However, in many practical cases, a full-wave representation of the physical antenna is unfeasible or unavailable in the format required by the desired CEM solver. This paper describes a procedure to derive, a computational efficient, full wave representation of an existing antenna for CEM solvers. The procedure is based on post-processing of the measured antenna pattern. The desired source antenna is measured while situated in a suitable environment, of reduced complexity and size, that locally resemble the final antenna environment. The measured field is expanded using equivalent currents and an equivalent near field (NF) source is derived in a volume conformal to the antenna. The NF source is a truthful representation of the measured source and highly suitable for CEM analysis. The procedure of generating the NF source from measurements is fully general and can be used for the installation of antennas in complex environments of arbitrary complexity. The procedure is illustrated and validated by an example concerning the placement of a monocone antenna (SMC2200) on an electrically large rectangular ground plane. The monocone antenna is initially measured on a small circular ground plane that resemble the final operational environment in the vicinity of the antenna. The measurement has been performed in a MVG multi probe spherical near field system. Simulations using the measured source on the larger rectangular structure have been compared with a full numerical model of the antenna and structure for verification. A further validation of the NF source method, based on the measurement of the larger rectangular structure is on-going.

Design improvements of electrically large antennas using the inverse source method

The equivalent radiating current technique (EQC) is based on an integral equation formulation of the inverse source problem upon rigorous application of the equivalence principle [1]-[7]. This method offers a greater generality and flexibility since it allows reconstructing sources on arbitrary 3-D surfaces enclosing the antenna under test (AUT). Indeed the equivalent source approach is a true 3D approach as opposed to traditional methods based on plane wave expansion using hemispherical field information. The equivalent current technique is highly applicable in the testing, validation and diagnostics of a wide variety of antennas. The visualization of the equivalent radiating currents on a surface conformal to the physical shape of the antenna is particularly useful to understand multi element array functioning and facilitate design improvements. This paper illustrate, by measured examples, the advantages of new enhancements of the method, which allow the user to process antennas with larger dimensions without scarifying accuracy and maintaining the dual equation formulation.

Echo Suppression by Spatial-Filtering Techniques in Advanced Planar and Spherical Near-Field Antenna Measurements [AMTA Corner]

This paper presents a comparative investigation of two versatile error-mitigation techniques, applicable to general antenna near-field measurement scenarios with echo signals of unknown origin. Both techniques are based on spatial filtering of the measured field, taking advantage of a priori knowledge of the antennas size. The first approach takes advantage of the spatial-filtering properties of the spherical-wave expansion of the measured field. The second approach is based on the reconstruction of equivalent currents, and implements the spatial filtering as a direct consequence of the selected size and shape of the reconstruction surface. The investigation was performed using measured data on two different horns in both planar and spherical near-field scanning geometries. The presence and levels of echo pollution in the measurements were controlled by introducing known scattering objects in the anechoic chambers, and comparing with reference situations without disturbance.

Antenna measurement processing for diagnostics and filtering based on integral equations

This communication presents promising applications of the integral equation formulation of the inverse source problem. The technique is based on the extraction of equivalent sources on a 3-D closed surface enclosing the Antenna Under Test (AUT) from near or far field measured radiation patterns upon rigorous application of the equivalence principle. Such sources allow malfunction detection and design improvements, investigation of abnormalities in antenna measurements, removal of unwanted radiation caused by spurious effects besides the more conventional Near Field-Far Field and Near Field-Near Field transformations. The main advantage of the integral equation formulation over the wave expansion technique is its geometry-independence, in principle being able to accommodate efficiently for atypical geometries (not uncommon in real applications) both for the radiator and the measurement range (including truncated versions of canonical ranges).

Automated Design and Experimental Validation of a Reconfigurable, Board-Mounted Compact Antenna

A quad-band compact, frequency-reconfigurable patch-type antenna is presented, designed to operate fully integrated on a full real-life printed circuit board (PCB), taking also into account the effect of a number of electronic components distributed on the board. Reconfigurability is obtained through a set of shorting pins switchable to the ground plane; the switches employ p-i-n diodes. The antenna is designed via an optimization process that jointly accounts for both patch shape and frequency. Reconfigurability in four subbands from 824 to 1990 MHz is achieved with two switches only, with an antenna space occupation of less than

Dual-port reconfigurable planar antennas for diversity and duplexing applications

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