Quasi-planar Antennas Research Articles

An Effective Near-Field to Far-Field Transformation with Planar Spiral Scanning for Flat Antennas under Test.

The goal of this article is to provide numerical and experimental assessments of an effective near-field to far-field transformation (NF-FF T) technique with planar spiral scanning for flat antennas under test (AUTs), which requires a non-redundant, i.e., minimum, number of NF measurements. This technique has its roots in the theory of non-redundant sampling representations of electromagnetic fields and was devised by suitably applying the unified theory of spiral scans for non-volumetric antennas to the case in which the considered AUT is modeled by a circular disk having its radius equal to half of the AUT's maximum dimension. It makes use of a 2D optimal sampling interpolation (OSI) formula to accurately determine the massive amount of NF data required by the classical plane-rectangular NF-FF T technique from the non-redundant data gathered along the spiral. It must be emphasized that, when considering flat AUTs, the developed transformation allows one to further and significantly save measurement time as compared to that required by the previously developed NF-FF T techniques with planar spiral scans based on a quasi-planar antenna modeling, because the number of turns of the spiral and that of NF data to be acquired depend somewhat on the area of the modeling surface. The reported numerical simulations assess the accuracy of the proposed NF-FF T technique, whereas the experimental tests prove its practical feasibility.

Pattern Reconstruction from Near-Field Data Affected by 3D Probe Positioning Errors Collected via Planar-Wide Mesh Scanning

An effective procedure to correct known 3D probe positioning errors affecting the near-field–far-field transformation (NF–FF) with non-conventional plane rectangular scanning, named planar wide-mesh scanning (PWMS), is developed in this paper. It relies on the non-redundant sampling representations of electromagnetic fields and related optimal sampling interpolation (OSI) expansions and has been devised when a quasi-planar antenna under test is considered as suitably modelled by either a double bowl or an oblate spheroid. Such an algorithm first makes use of the so-called k-correction to compensate for the errors occurring when the actual sampling points deviate from the acquisition plane and then adopts an iterative procedure to restore the NF samples at the points specified by the used non-redundant sampling representation from those obtained at the previous step and affected by 2D positioning errors. Finally, once the regularly arranged PWMS samples have been calculated, the NF data required to compute the classic plane-rectangular NF–FF transformation are accurately evaluated by using an effective 2D OSI algorithm. Several numerical results are presented in order to assess the effectiveness of the devised approach.

Prediction of the far field radiated by a flat antenna under test from a reduced set of near‐field bi‐polar measurements

In this article, a bi-polar near-field-to-far-field (NFTFF) transformation with probe compensation, which is very convenient from the data reduction standpoint when characterising a flat antenna under test (AUT), is developed. It takes advantage from the non-redundant sampling representations of the electromagnetic fields to devise a sampling representation on the scanning plane, which requires the knowledge of the bi-polar NF samples at a reduced number of sampling points. To account for the AUT geometry, it properly adopts as modelling surface a disc having diameter equal to the largest size of such an AUT. This surface allows a more effective AUT modelling from the NF data reduction standpoint than the formerly proposed modelling surfaces for quasi-planar antennas (the oblate ellipsoid or the two-bowls), because, unlike these last, it has the capability to best fit the AUT geometry, thus reducing very significantly the involved volumetric redundancy. An ad hoc developed two-dimensional optimal sampling, interpolation formula is then employed to reconstruct the plane-rectangular NF data which would be necessary to execute the classical NFTFF transformation developed by Leach and Paris. Some results of numerical simulations and experimental proofs are reported to demonstrate the efficiency of the so developed technique.

Optimization of the near-field spherical spiral scanning for the radiation pattern reconstruction of an offset quasi-planar antenna

An optimization of the near-field data acquisition on a spherical spiral for recovering the radiation pattern of a quasi-planar antenna, which is non-centred with respect to the scanning system, is here presented. As a matter of fact, such an unusual antenna positioning reflects negatively on the number of the needed near-field data, since this last depends on the smallest spherical surface enclosing the antenna under test and sharing the same centre as the scanning surface. The proposed optimization reduces such a number through a non-redundant sampling representation of the measured voltage adopting a suitable source modelling. The so collected samples are then employed in a two-dimensional optimal sampling interpolation algorithm for retrieving the near-field data indispensable to carry out the classical near-field to far-field transformation. Numerical and experimental tests endorse the effectiveness of the proposed method.

Pattern Evaluation From NF Spherical Spiral Data in the Noncentered Quasi-Planar Antennas Case

The far-field reconstruction of noncentered quasi-planar antennas is here addressed by using a spherical spiral scan in the near-field region. A reduction of the near-field data is achieved by suitably exploiting the unified theory of spiral scannings for nonspherical antennas. Such a technique, relying on the nonredundant representation of electromagnetic fields, adopts an oblate spheroid as source modeling and uses a two-dimensional optimal sampling interpolation algorithm to recover the data needed to execute the classical near-field–far-field transformation. In this case, the reduction process is required since an inadequate mounting system increases the number of needed data when compared to facilities, which allow one to center the antenna under test with respect to the spherical scanning surface. The above-mentioned statement is based on the following rule: the classical near-field–far-field transformation requires a number of data depending on the smallest spherical surface, which encloses the antenna and shares the same center as the scanning surface. The reported results thoroughly prove the efficacy of the developed technique.

A Spherical Near-to-far-Field Transformation Using a Non-Redundant Voltage Representation Optimized for Non-Centered Mounted Quasi-Planar Antennas

This research falls in the antenna measurements related topic, and deals with the problem occurring in the classical spherical near-to-far-field (NTFF) transformation, when it becomes unpractical to mount the antenna under test (AUT) with its center at the center of the scanning sphere. This issue reflects in a growth of the number of near-field (NF) samples to be acquired, since this number depends on the radius of the minimum sphere, which contains the antenna, and is centered at the scanning sphere center. The non-redundant sampling representations of the electromagnetic field are conveniently exploited, to develop an effective spherical NTFF transformation for non-centered AUTs with quasi-planar geometry, requiring a minimum amount of NF samples, and nearly the same as that for a centered mounting of the AUT. Then, the NF data needed to perform the classical NTFF transformation are determined in efficient way from the acquired non-redundant NF samples by employing an accurate 2-D sampling interpolation scheme. Thus, it is possible to significantly save measurement time. Some simulation and laboratory results are reported to show the effectiveness of the developed technique, which takes into account a non-centered AUT mounting.

A Non-Redundant Sampling Representation Requiring the Same Number of Spherical Near-Field Measurements for Both Onset and Offset Mountings of a Quasi-Planar Antenna

An effective non-redundant near-field to far-field transformation (NFTFFT) with spherical scan, which accounts for the offset mounting of a quasi-planar antenna and employs the same number of NF data as in the case of onset mounting, is developed in this paper. The interest for this NFTFFT arises from the fact that the mounting where the antenna and the measurement sphere centers coincide could result to be impracticable. In this case, the amount of NF data required by the traditional spherical NFTFFT can significantly increase. In the proposed NFTFFT, this drawback has been overcome by accurately recovering these NF data from the collected non-redundant ones via a sampling expansion, obtained by exploiting the non-redundant sampling representations and assuming the antenna as enclosed in an oblate spheroid. Numerical and experimental results assessing the effectiveness of the developed technique are reported.

Laboratory testing of an SVD‐based approach to recover the non‐redundant bi‐polar NF data from the positioning error affected ones

This study deals with the problem of the correction of known probe positioning errors, which can occur in an actual planar near-field facility when adopting a non-redundant near-field to far-field (NFTFF) transformation with a bi-polar scan for quasi-planar antennas. To this end, a singular value decomposition based approach is developed to recover the uniform bi-polar samples, whose position is set by the non-redundant sampling representation got by shaping the antenna with a double bowl, from those affected by positioning errors. Then, a 2D optimal sampling interpolation formula is used to accurately reconstruct the plane rectangular near-field data needed by the standard NFTFF transformation from the retrieved non-redundant uniform samples. Experimental results, assessing the capability of the developed procedure to correct even pessimistic positioning errors, are shown.

Microstrip Antenna Array Fed by a Low-Loss Gap-Waveguide Feed Network

A Ku-band quasi-planar microstrip antenna array fed by a gap-waveguide feed network is demonstrated. The upper microstrip substrate is not in electric contact with the lower feed network, which relaxes the fabrication process considerably. The 64-element array consists of 16 2-by-2 subarrays arranged to form an 8-by-8 configuration of array elements. To ensure minimum feed losses, the subarrays are excited by a corporate feed network composed of groove-gap-waveguide components. The first part of the feed network consists of the ground plane of the antenna array which also plays the role of the upper plate of the waveguide network. The second part is an artificial magnetic conductor (AMC) structure realized within the lower plate of the waveguide feed network via milling. In this communication, the AMC structure is made of a bed-of-nails. Array elements are rectangular patches showing 8.85 dBi gain each at the center frequency. The maximum measured gain of the antenna array is 26.18 dBi, which is equivalent to 57.81% aperture efficiency.

Fast and Accurate Far-Field Prediction by Using a Reduced Number of Bipolar Measurements

This letter gives the experimental assessment of a near-to-far-field transformation (NTFFT) technique allowing the fast and accurate reconstruction of the antenna far field from a nonredundant, i.e., minimum number of near-field (NF) data collected through a bipolar scanning. Such a NTFFT relies on a nonredundant sampling representation of the voltage detected by the scanning probe, attained by shaping the antenna with an oblate ellipsoid, a model suitable to deal with quasi-planar antennas, as typically are the measured ones in a planar NF facility. The NF data necessary to execute the traditional plane-rectangular NTFFT are then effectively recovered from the acquired (nonredundant) bipolar ones by exploiting a 2-D optimal sampling interpolation formula. This makes possible to achieve a remarkable acquisition time saving, which is a very relevant outcome, because this time is nowadays much greater than that needed to carry out the NTFFT.

Two Effective Approaches to Correct the Positioning Errors in a Spherical Near-Field–Far-Field Transformation

ABSTRACTTwo techniques are developed to efficiently compensate known positioning errors affecting the near-field measurements in a non-redundant spherical near-field–far-field transformation for quasi-planar antennas, and they are fully assessed through numerical and experimental tests. They rely on a non-redundant sampling representation of the voltage measured by the probe, obtained by assuming that the antenna is enclosed in a surface formed by two circular bowls with the same aperture diameter. Both techniques use a two-step procedure. In the first step, the near-field data at the points fixed by the sampling representation are recovered from the irregularly spaced measured ones by properly applying an iterative technique or the singular value decomposition method. Then the near-field data needed by the standard spherical near-field–far-field transformation are effectively reconstructed by means of an optimal sampling interpolation algorithm.

Far-Field Pattern Reconstruction From a Nonredundant Plane-Polar Near-Field Sampling Arrangement: Experimental Testing

An efficient probe-compensated near-field–far-field (NF–FF) transformation with plane-polar scanning, particularly suitable for quasi-planar antennas, is experimentally assessed in this letter. It exploits the nonredundant sampling representations of electromagnetic fields and adopts an oblate ellipsoid to model the antenna under test. A two-dimensional optimal sampling interpolation expansion is employed to accurately recover the NF data needed by the standard plane-rectangular NF–FF transformation from the nonredundant plane-polar ones collected by the probe. A remarkable reduction of the number of NF data to be acquired and of the related measurement time is so obtainable. Some results of the experimental tests, performed at the UNISA Antenna Characterization Lab and assessing the effectiveness of such a NF–FF transformation technique, are reported.

A CPW-Fed Quasi-PIFA Antenna Using Quasi-Lumped Resonators for Mobile Phones

A novel single CPW-fed Quasi-Planar Inverted-F Antenna (PIFA) using quasi-lumped elements is developed for mobile communication handheld terminals operating at 2.6 GHz. The antenna is composed of an inductor covered by a set of interdigital and parasitic capacitors. The proposed antenna achieves a measured bandwidth of 11% for return loss with the antenna gain of about 4 dBi. The antenna is designed in single layer (zero height) which is appropriate to be used in thin devices where a small room is considered for the antenna. The proposed antenna is suitable for use in Long Term Evolution band 7. The operating frequency of introduced antenna depends on the number of interdigital fingers and inductor length rather than the total resonator patch only, so that the operating frequency can be altered while the total patch size remains unchanged. The calculated operating frequency is confirmed by simulation and measurement. Also the dipole-like simulated radiation pattern is confirmed by measurement.

The Lateral Wave Antenna

This paper introduces a quasi-planar antenna that provides, over a broad frequency bandwidth, highly directive radiation in one plane, phase center stability as a function of the frequency and high efficiency. The structure is composed by a dielectrically filled parallel plate waveguide that supports the propagation of a transverse electromagnetic (TEM) wave. The waveguide is truncated and shaped as a planar lens to achieve directive beams in the H-plane, while a short flaring is added at the waveguide open end to facilitate radiation into free space. High efficiency is achieved thanks to the peculiar feed structure that supports the propagation of directive lateral waves. An antenna prototype has been manufactured and measured. The results highlight the highest directivity for a quasi-planar broadband antenna (3:1 bandwidth) with very low dispersion and frequency-stable phase center.

AN ULTRA-WIDEBAND QUASI-PLANAR ANTENNA WITH ENHANCED GAIN

A new ultra-wideband antenna with enhanced and nearly constant gain is presented. This quasi-planar antenna is composed of a CPW-fed printed monopole and a short horn, both made out of a single substrate. The measurements demonstrate an almost ∞at peak gain of 5:5dBi § 0:7dB from 2.5GHz to 15GHz with the average gain difierence in XZ plane is roughly 2dB up to 8GHz, which further rise to 6dB at 10GHz. The antenna also has a nearly linear phase response in this band. Well tested performance both in frequency and time domains, along with broad azimuth pattern, results in minimal ringing of a radiated pulse. The new antenna is suitable for establishing good line of sight link for UWB transmission and other broadband applications.

Far-Field Pattern Reconstruction from Near-Field Data Collected via a Nonconventional Plane-Rectangular Scanning: Experimental Testing

This paper deals with the experimental validation of an efficient near-field-far-field (NF-FF) transformation using the planar wide-mesh scanning (PWMS). Such a nonconventional plane-rectangular scanning technique is so named, since the sample grid is characterized by meshes wider and wider when going away from the center, and makes it possible to lower the number of needed measurements, as well as the time required for the data acquisition when dealing with quasi-planar antennas. It relies on the use of the nonredundant sampling representations of electromagnetic fields which employ an oblate ellipsoid or a surface formed by two circular “bowls” with the same aperture diameter but eventually different bending radii to shape a quasi-planar antenna. A two-dimensional optimal sampling interpolation formula allows the reconstruction of the NF data at any point on the measurement plane and, in particular, at those required by the classical NF-FF transformation with the conventional plane-rectangular scanning. The measurements, performed at the planar NF facility of the antenna characterization laboratories of Selex ES, have confirmed the effectiveness of this innovative scanning also from the experimental viewpoint.

Non-Redundant Spherical NF - FF Transformations Using Ellipsoidal Antenna Modeling: Experimental Assessments [Measurements Corner

Two non-redundant near-field-to-far-field (NF-FF) transformation techniques with spherical scanning, for antennas having a dimension very different from the other ones, are experiment ally tested in this paper. These techniques are based on the non-redundant sampling representations of the electromagnetic fields. They use a rotational ellipsoid to shape non-spherical antennas: a prolate ellipsoid for elongated antennas, and an oblate ellipsoid for the quasi-planar antennas. A two-dimensional optimal-sampling interpolation formula is employed to accurately recover the near-field data required by the classical spherical near-field-to-far-field transformation from the non-redundant near-field data. It is so possible to obtain a remarkable reduction in the number of the near-field samples to be acquired and, as a consequence, a remarkable reduction in the measurement time. Some experimental results, carried out at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of the proposed techniques, are shown.

Experimental Assessment of an Effective Near-Field–Far-Field Transformation With Spherical Spiral Scanning for Quasi-Planar Antennas

Experimental tests on a near-field-far-field (NF-FF) transformation technique with spherical spiral scanning suitable for quasi-planar antennas are presented in this letter. Such a technique is based on the nonredundant sampling representations of the electromagnetic fields and employs an oblate ellipsoid to model the antenna under test. A two-dimensional optimal sampling interpolation formula is then employed to recover the NF data at any point on the scanning sphere and, in particular, at those needed by the classical spherical NF-FF transformation. It is so possible to lower the number of needed measurements, as well as the time required to acquire the data. Both the reported NF and FF reconstructions assess the effectiveness of the technique.

FAR-FIELD RECONSTRUCTION FROM NEAR-FIELD DATA ACQUIRED VIA A FAST SPHERICAL SPIRAL SCAN: EXPERIMENTAL EVIDENCES

A probe-compensated near-fleld-far-fleld (NF-FF) trans- formation with spherical spiral scanning, which makes possible to lower the number of needed measurements, as well as the time required for the data acquisition when characterizing quasi-planar antennas, is experimentally verifled in this paper. Such a technique, based on the nonredundant representation of electromagnetic flelds, has been achieved by properly applying the unifled theory of spiral scans for nonspherical antennas and adopting a very ∞exible source modelling, formed by two circular \bowls with the same aperture diameter but difierent bending radii. A two-dimensional optimal sampling interpo- lation formula allows one to reconstruct the NF data at any point on the measurement sphere and, in particular, at those required by the classical NF-FF transformation with spherical scanning. The reported NF and FF reconstructions, obtained from the nonredundant samples acquired on the spiral, assess the accuracy of the proposed technique.

FAR-FIELD RECONSTRUCTION FROM A MINIMUM NUMBER OF SPHERICAL SPIRAL DATA USING EFFECTIVE ANTENNA MODELINGS

Two probe-compensated near-field-far-field transforma- tions with spherical spiral scanning tailored for antennas having two of their dimensions very different from the third one are developed by properly applying the unified theory of spiral scans for nonspheri- cal antennas. One is suitable for electrically long antennas, which are considered as enclosed in a cylinder ended in two half-spheres. The other adopts a surface formed by two circular bowls with the same aperture diameter but different lateral bends to shape a quasi-planar antenna. These flexible modelings fit very well many actual antennas by properly setting their geometric parameters. Great reduction of the number of data to be acquired is achieved, thus significantly re- ducing the required measurement time. Numerical tests validating the accuracy of the proposed techniques and their stability with respect to random errors affecting the data are shown.