The paper introduces the use of Non-Uniform Fast Fourier Transform (NUFFT) routines in “complex” (i.e., amplitude and phase) and phaseless Near-Field/Far-Field transformations. The use of those routines results computationally very convenient when non-regular field sampling prevents the use of standard FFTs. The attention is focused on a plane-polar acquisition geometry. Numerical and experimental results show the effectiveness of the developed algorithms.

/pdf/nufft-accelerated-plane-polar-also-phaseless-near-field-far-33j778og88.pdf

NUFFT-Accelerated Plane-Polar (Also Phaseless) Near-Field/Far-Field Transformation

Phase-retrieval from measured phaseless field data is of interest for various applications including electromagnetic dosimetry, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. In this study two phaseretrieval methods are compared. The first method, the adjoint field method, employs a gradient-based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, uses an optimization algorithm based on the phase angle gradients of a functional. The methods are tested with numerical test cases and the phase angle gradient method is found to retrieve the phase with the best accuracy. Moreover it gives results that agree well with correct phase.

/pdf/comparison-between-two-phase-retrieval-methods-for-4gtsdjuggk.pdf

Comparison Between Two Phase-Retrieval Methods for Electromagnetic Source Modeling

A technique for wavelength measurement of microwaves is demonstrated. The wavelength is obtained from an interference pattern monitored by an IR Camera. The data captured by the camera is stored in a computer attached to it. This data is then processed for wavelength calculation. In order to show the utility of the above technique, two cases are demonstrated: Case (1) Interference pattern of two patch antennas each radiating at 8 GHz. Case (2) Interference pattern from a single antenna, radiating at 12 Ghz, kept in front of a metallic sheet with two slits. The simulation is carried in CST Microwave Studio software. A good agreement between simulation and experimental results is seen.

Infrared thermography for determination of wavelength of microwave signals from interference pattern

Detection of polarisation of microwave signals using infrared thermography is described in this paper. A metal grating consisting of parallel, equally spaced metallic strips is placed in between a microwave source (antenna) and a microwave absorption screen for permitting the determination of direction of electric field vector (polarisation). Very low frequency modulation of the microwave source is added to permit lock-in thermography which enhances thermal resolution.In case of linear polarisation when the metallic strips of the grating are parallel to the direction of electric field vector, the temperature rise on the screen as observed by an infrared camera, is minimum. On the other hand if the metallic strips are perpendicular to the electric field vector the temperature rise observed on the screen is maximum. The orientation of the grid is changed by rotating the grid about a central axis perpendicular to its plane. With each different orientation of the grid a change in temperature rise is o...

Determination of Polarisation of Microwave Signals by Lock-in Infrared Thermography

The Phase Angle Gradient Method (PAGM) is a recent technique developed for phase retrieval based on amplitude-only measurement data. Preliminary results have shown that the PAGM is able to perform phase retrieval at 100MHz with accurate phase information based on measured fIeld components on three planar surfaces. In this paper, a performance evaluation of the PAGM under different conFigurations is conducted. Phase retrieval based on field measurements for different plane sizes and separations between the planes are studied rigorously. In addition, the PAGM is tested for different initial phase distributions. The results show that the PAGM is capable of retrieving phase information even if the separation between the measurement planes is small in terms of wavelengths.

https://www.jpier.org/pierb/pierb25/07.10070205.pdf

Performance Evaluation of Phase-Angle Gradient Method for Phase Retrieval based on Low-Frequency amplitude-Only Near-Field Data

The framework of our work is the application of a fast method to estimate the radiation pattern of an antenna from the measurement of the electric-fleld magnitude in the near-fleld region using infrared (IR) camera. IR acquisition techniques allows quasi- realtime measurements of the magnitude of the electrical fleld on planar surfaces in near-fleld conditions. However the antennas radiation patterns can only be estimated from near-fleld electrical magnitude and phase measurements. Consequently a classical plane to plane iterative phase retrieval process has been developed and tested with respect to a large number of conflguration parameters such as to flnd an optimal conflguration on a wide frequency range (0.5{20GHz). In order to achieve and validate such a study, some comparisons have been performed on data obtained either by numerical simulation or classical near-fleld technique based upon radio-frequency (RF) probe scanning on simple horn antennas. Among all the studied parameters we will focus onto the in∞uence of the dynamic range of the measurements on the reconstructed radiation patterns and on validations from experimental results.

/pdf/wideband-validation-of-a-phase-retrieval-process-applied-to-4edveqcbol.pdf

Patrick Levesque

Papers

Wideband validation of a phase retrieval process applied to infrared planar near- field measurements