Performance evaluation of phase-angle gradient method for phase retrieval based on low-frequency amplitude-only near-field data

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

On the Forward Scattering of Microwave Breast Imaging

Microwave imaging for breast cancer detection has been of significant interest for the last two decades. Recent studies focus on solving the imaging problem using an inverse scattering approach. Efforts have mainly been focused on the development of the inverse scattering algorithms, experimental setup, antenna design and clinical trials. However, the success of microwave breast imaging also heavily relies on the quality of the forward data such that the tumor inside the breast volume is well illuminated. In this work, a numerical study of the forward scattering data is conducted. The scattering behavior of simple breast models under different polarization states and aspect angles of illumination are considered. Numerical results have demonstrated that better data contrast could be obtained when the breast volume is illuminated using cross-polarized components in linear polarization basis or the copolarized components in the circular polarization basis

Comparison between two phase-retrieval methods for electromagnetic source modeling

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 phase-retrieval methods, namely the adjoint field method and the phase angle gradient method, are compared using 3D numerical test cases. The methods were previously presented by us, but the adjoint field method was at that time only implemented in 2D. In this study the adjoint field method has been extended to 3D, which makes it possible to test the method for more realistic test cases and to compare it with the phase angle gradient method. The results show that the phase angle gradient method is able to retrieve the phase with better accuracy than the adjoint field method. Moreover it gives results that agree well with correct phase. The phase angle gradient method was also tested with measured magnetic field. The obtained phase angles on a measurement plane in front of the source gave calculated field amplitudes that agree well with measured field

Ultra Wideband Transient Scattering and Its Applications to Automated Target Recognition

Reliable radar target recognition has long been the holy grail of electromagnetic sensors. Target recognition based on the singularity expansion method (SEM) uses a time-domain electromagnetic signature and has been well studied over the last few decades. The SEM describes the late time period of the transient target signature as a sum of damped exponentials with natural resonant frequencies (NRFs). The aspect-independent and purely target geometry and material-dependent nature of the NRF set make it an excellent feature set for target characterization. In this chapter, we aim to review the background and the state of the art of resonance-based target recognition. The theoretical framework of SEM is introduced, followed by signal processing techniques that retrieve the target-dependent NRFs embedded in the transient electromagnetic target signatures. The extinction pulse, a well-known target recognition technique, is discussed. This chapter covers recent developments in using a polarimetric signature for target recognition, as well as using NRFs for subsurface sensing applications. The chapter concludes with some highlights of the ongoing challenges in the field

Characterization of Radar Target Using Multiple Ultra Wideband Transient Responses

The aspect independency nature of the natural resonance embedded in transient signatures of radar targets allows it to be an excellent candidate for target characterization and recognition. The amplitudes of these resonance modes, however, vary as a function of the excitation aspects and polarization states such that these modes could be poorly excited under certain configurations. To ensure the dominant modes are well excited and included in target characterization, one way is to illuminate the target over a number of aspects and polarization states and perform resonance extraction over the large number of target signatures. In this letter, we aim to evaluate an optimal solution to handle such large amount of data from multiple-Aspect multiple-polarization measurements. Different ways to handle the data are explored and exemplified using a simple dielectric target

Characterization of Radar Targets Based on Ultra Wideband Polarimetric Transient Signatures

Resonance based target recognition has been well studied for the last three decades. The purely target dependent natural resonant frequencies are used as a feature set for target classification. Such technique may fail if the targets of interest have similar or almost the same resonant frequencies. In this paper, the idea of using the polarimetric features at the resonant frequencies is investigated and demonstrated via numerical examples