Surface Wave Multipath Signals in Near-Field Microwave Imaging

Abstract

Microwave imaging techniques are prone to signal corruption from unwanted multipath signals. Near-field systems are especially vulnerable because signals can scatter and reflect from structural objects within or on the boundary of the imaging zone. These issues are further exacerbated when surface waves are generated with the potential of propagating along the transmitting and receiving antenna feed lines and other low-loss paths. In this paper, we analyze the contributions of multi-path signals arising from surface wave effects. Specifically, experiments were conducted with a near-field microwave imaging array positioned at variable heights from the floor of a coupling fluid tank. Antenna arrays with different feed line lengths in the fluid were also evaluated. The results show that surface waves corrupt the received signals over the longest transmission distances across the measurement array. However, the surface wave effects can be eliminated provided the feed line lengths are sufficiently long independently of the distance of the transmitting/receiving antenna tips from the imaging tank floor. Theoretical predictions confirm the experimental observations.

Integration of microwave tomography with magnetic resonance for improved breast imaging

“…2(a)]. As described in more detail elsewhere, 69 this configuration generated multipath signals resulting from surface wave propagation (down and up the outside of the coaxial feedlines) along the tank base/liquid interface. A minimum feedline length of 9.0 cm in the lossy liquid was found to attenuate these surface currents to a level comparable to our deeper standalone MT antenna chamber.…”

3D parallel-detection microwave tomography for clinical breast imaging

“…The lossy (glycerin/water) coupling-medium acts primarily as a matching fluid to limit scatter at the breast boundary, 43 but offers the added benefit of reducing multipath signals and debilitating mutual coupling. 32 Transferring liquid into and out of the chamber uses an automated pumping system (Baldor Industrial custom DC isolated pump, Fort Smith, Arizona, USA).…”

“…Two systems successfully solved the under-appreciated challenge of multipath signals either using algorithmic processing 31 or suppression through attenuation in a lossy coupling-medium. 32 Problems with mutual coupling of adjacent antenna-array elements have also been reported. 33 Work by Franza et al 34 and Meaney et al 35,36 have extensively studied and addressed this issue.…”

Electrical Characterization of Glycerin: Water Mixtures: Implications for Use as a Coupling Medium in Microwave Tomography

“…The lower permittivity liquids such as oils have been intended for coupling to lower water content tissues such as the breast while water and saline are utilized for higher property tissues. Over time, appreciation of the impact of multi-path signals and their ability to corrupt desired measurements has increased [9],[10]. One approach has fabricated a miniature anechoic chamber around the target zone and antennas to suppress the unwanted reflections [1].…”