Stuart Gregson

Behaviour of orthogonal wave functions and the correction of antenna measurements taken in non-anechoic environments

The measurement and post-processing mode orthogonalisation and filtering technique, named Mathematical Absorber Reflection Suppression (MARS), has been used extensively to identify and subsequently extract measurement artefacts arising from spurious scattered fields that are admitted when antenna testing is performed in non-ideal anechoic environments. Underpinning the success of the MARS post-processing, and other mode orthogonalisation and filtering strategies, is the behaviour of the orthogonal vector wave (mode) expansions that are employed to describe the radiated fields and in particular their behaviour under the isometric coordinate translations that are central to the post processing. Within this paper, simulated and measured data will be used to illustrate the applicability of this measurement and post processing technique paying particular attention to the behaviour of the various modal expansions examining and confirming specific, commonly encountered, measurement conventions.

Compact range quiet zone modelling: Quantitative assessment using a variety of electromagnetic simulation methods

This paper presents the results of a recent computational electromagnetic (CEM) simulation campaign for a single offset reflector CATR, where a number of models employing different field propagation methods were compared and contrasted both qualitatively and quantitatively using objective, non-local statistical image classification techniques.

Application of Mathematical Absorber Reflection Suppression to far-field antenna measurements

For some time now, a technique named Mathematical Absorber Reflection Suppression (MARS) has been used successfully to identify and then suppress range multi-path effects in spherical [1, 2, 3, 4], cylindrical [5, 6, 7], and planar [8, 9] near-field antenna measurement systems. This paper details a recent advance that, for the first time, allows the MARS measurement and post-processing technique to be successfully deployed to correct antenna pattern data taken using direct far-field or compact antenna test ranges (CATRs) where only a single great circle cut is acquired. This paper provides an overview of the measurement and novel data transformation and post-processing chain that is utilised within the far-field MARS (F-MARS) technique to efficiently correct far-field, frequency domain data. Preliminary results of range measurements that illustrate the success of the technique are presented and discussed.

Proposal for a novel near-field antenna measurement technique employing a conic frustum geometry

A technique for the prediction of far-field antenna patterns from data obtained from modified plane-polar near- field measurement system is proposed. This technique utilises a simple change in facility alignment to enable near-field data to be taken over the surface of a conceptual right conic frustum. In this way, existing planar facilities can be modified so that they are able to characterise the wide angle antenna performance in situations where hitherto they would have been limited by truncation. Furthermore, this system offers a cost effective solution to the characterisation of a class of antenna that currently can only be effectively served with spherical near-field scanning. This paper presents the measurement technique, proposes the probe corrected transformation algorithm and presents preliminary results before outlining the future work.

Computational electromagnetic model of a cylindrical near-field antenna test system: Examination of common measurement errors and their compensation

This paper presents the results of a new computational electromagnetic simulation of a cylindrical near-field antenna test system. The new plane-wave spectrum representation based simulation allows many of the commonly encountered components within the range uncertainty budget to be included within the model. These terms are: range reflections, random errors and cylindrical measurement truncation. This paper presents the results of simulations that verify the utility of the cylindrical mathematical absorber reflection suppression (C-MARS) technique for compensation of their effects. Although past verifications have been done using experimental techniques this paper, for the first time, corroborates these findings using purely computational methods.

Extending cylindrical mathematical absorber reflection suppression to further reduce range scattering errors

Recent work in developing a mode orthogonalisation and filtering post processing algorithm for multipath suppression in far-field and planar near-field antenna measurement systems has enabled worthwhile improvements to be obtained from the analogous, but mathematically and computationally distinct, cylindrical analogue. This paper presents an overview of the measurement and novel post-processing algorithm as embodied within the cylindrical mathematical absorber reflection suppression technique as well as comparing and contrasting results obtained from the new post-processing algorithms with previously published data.

Examination of the Effectiveness of Far-field Mathematical Absorber Reflection Suppression in a CATR Through Electromagnetic Simulation

For more than a decade now, a measurement and post‐processing technique involving modal filtering, named Mathematical Absorber Reflection Suppression (MARS), has been used very successfully to identify and subsequently extract range reflections in spherical, cylindrical and planar near‐field antenna test systems and far‐field and compact antenna test ranges. Much of the early work concentrated on verification through experimental testing however some additional validation was performed using computational electromagnetic simulations. These considered first far‐field and subsequently near‐field cases. The recent development of an accurate, flexible electromagnetic simulation tool that enables the simulation of “measured” far‐field pattern data as obtained from using a compact antenna test range (CATR) has, for the first time, permitted the careful verification of the far‐field MARS technique for a specified AUT and CATR combination. This paper presents simulated “measured” far‐field antenna pattern data in the presence of a large scatterer and then verifies the successful extraction of the scattering artefacts. In addition to considering range reflections, feed spill‐over is also treated. Results are presented and discussed.

Cylindrical near-field antenna measurements

This chapter has presented a development of the standard probe-corrected cylindrical near-field antenna measurement theory. The great advantage of the cylindrical approach is that it is instantly applicable to testing antennas for which it is desired to compute the complete 360o far-field azimuthal pattern. However, for the class of antennas that do not satisfy this directivity requirement, recourse must be sought in spherical near-field antenna testing which is developed.

Planar near-field antenna measurements

This chapter discusses the so-called planar near-field antenna test range. This implies that the planar near-field range is only a useful tool if it is used for highly directive antennas where it can be assumed that by far the vast majority of the radiated power is incident on the plane over which the data is sampled.

Near-field range assessment

The uncertainty concepts described in this chapter form the basis of any range assessment (RA), regardless of the type of test facility and therefore allow us to create a framework within which the quality of any antenna measurement result can be expressed. It also allows us to do meaningful range inter-comparisons that have become such an integral part of modern test programmes. Although most of the groundwork related to RAs was conducted in an effort to validate near-field testing in the early days, this work has found wider application and can today be applied to far-field and CATR test systems with equal success. It is safe to say that the antenna measurement community (for the most part) have adopted the principle that measurement results need to be reported with an associated uncertainty, to make them credible.Finally, a very welcome side effect of doing any RA is a greater understanding of the measurement process and associated weaknesses. This often leads to a clear definition of exactly what aspect needs to be addressed if uncertainty is to be reduced, making for a very efficient use of resources in the process.