25-045 Use of frequency axis to improve antenna radiation characterization

Mission

The characterization of the field emitted by radiating systems remains an important step for the validation of manufactured equipment or for the proof of concept. The level of complexity of the characterization to be performed is logically dependent on the applicant's expectations and the characteristics of the device to be measured.

All these inputs need a specific analysis which leads to the definition of the properties to be verified by the measurement facility, the choice of the measurement technique, and the estimation of the operational constraints. This last point is a crucial element in defining the acceptability of the measurement campaign. Indeed, a measurement campaign may be technically feasible, but unacceptable in practice if its duration is excessive. In this general framework, many research activities continue to be carried out to increase the efficiency of measurement infrastructures.

A typical strategy is to reduce measurement times by decreasing the number of sampling points while maintaining the same level of accuracy. The used methods are then based on a parsimony of the measurement points taken from the sampling surface. This sparsity is defined by rules related to the dimensions of the antenna or by more complex analyses which integrate its geometry. The solution to the initial problem is therefore obtained by linking the 3 degrees of freedom of space corresponding to the location of the measurement points and the more or less simplified geometry of the antenna to be tested.

It is worth noting that, in these approaches, the solution obtained is implemented for the entire frequency range of interest of the radiating system and the associated treatment methods are commonly managed frequency-wise. Indeed, using a frequency-dependent sampling grid would be counterproductive while the objective is to reduce the number of points to be measured.

The common practice is then to define the measurement plan considering the most restrictive case, i.e., the highest frequency.

In this project, we propose to integrate the use of the frequency axis in addition to the mechanical positioning axes to improve the efficiency of measurement campaigns, in particular for:

• Proposing faster measurement plans by integrating the frequency axis as one of the axes defining the measurement sampling, strongly dimensioning from an acquisition time point of view.
• Improving accuracy: studying the gain in accuracy for a given sampling plan would reduce the impact of the signal-to-noise ratio during measurement. This would relieve the constraint on the dynamics of the measurement chains and therefore on the measurement time when data averaging or IF filtering are used.
• Reducing measurement times: A reduction in the number of frequency points would speed up the frequency scan time of the measurement chain, requiring interpolation along the frequency axis.

Multi-frequency techniques are currently largely under-represented in the field of antenna measurement in relation to the idea of reducing the number of measurement points. Indeed, while these techniques are widespread from a filtering point of view (time windowing, matrix pencil), existing studies on the acceleration of measurements are based on so-called harmonic approaches, with a fixed frequency.

The antenna measurement technique to be developed in this work will be applied to spherical far field (compact antenna test range) or near field measurement techniques, with a possible application for some parts to planar near-field measurements.

The experimental validations will be carried out within the M²ARS facility unit, using existing antenna test facilities: CAMILL (compact antenna test range in millimeter wave range), CACENDRA (near-field or far-field spherical measurements), and IDEM (planar near-field scanners).

The test cases of interest will present different degrees of complexity to validate the developments according to an agile process, ranging from an initial level of the standard horn antenna type to a final level of the antenna with beam tilting capabilities.

To sum up, this PhD thesis aims to add the frequency axis to the classical sampling axes. The objective is not to only consider frequency as a constrained parameter related to measurement requirements but as a degree of freedom to develop new data processing tools and measurement procedures. More generally, this project topic is part of a prospective augmented models to propose effective tools to meet expectations in antenna characterization and optimization of metrological resources.

It is worth noting that this PhD proposal is a logical continuation of Nicolas Mézières’ work entitled “Contributions to fast and accurate antenna characterization,” supported by CNES and LNE, as well as two Recherche and Technologie CNES actions on antenna characterization procedures.

For more information about the topics and the co-financial partner (found by the lab!):

contact Directeur de thèse - renaud.loison@insa-rennes.fr

Then, prepare a resume, a recent transcript, and a reference letter from your M2 supervisor/engineering school director and you will be ready to apply online before March 14th, 2025, Midnight Paris time!

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CNES will inform about the status of your application in mid-June. More details on CNES website: CNES Doctoral Grants