Current Issue : October - December Volume : 2019 Issue Number : 4 Articles : 5 Articles
This paper presents a new planar feeding structure for wideband resonant-cavity antennas\n(RCAs). The feeding structure consists of two stacked dielectric slabs with an air-gap in between.\nA U-shaped slot, etched in the top metal-cladding over the upper dielectric slab, is fed by a planar\nstripline printed on the back side of the dielectric slab. The lower dielectric slab backed by a ground\nplane, is used to reduce back radiation. To validate the wideband performance of the new structure,\nin an RCA configuration, it was integrated with a wideband all-dielectric single-layer partially\nreflecting superstructure (PRS) with a transverse permittivity gradient (TPG). The single-layerRCAfed\nby the U-slot feeding structure demonstrated a peak directivity of 18.5 dBi with a 3 dB directivity\nbandwidth of 32%. An RCA prototype was fabricated and experimental results are presented....
This paper proposes a technique to enhance the bandwidth and gain of an endfire radiating\nopen-ended waveguide using a thin slow-wave surface plasmon structure. Mounted in the E-plane\nof the stated waveguide, a thin corrugated slow-wave structure has been used in conjunction with a\nwaveguide transition to generate an endfire electromagnetic beam. An efficient mode conversion\nfrom waveguide transition to the corrugate plate resulted in the improved performance of the design.\nAn impedance bandwidth from 8 GHz to 18 GHz has been achieved along with a gain enhancement\nfrom 7 dBi to 14.8 dBi using the proposed hybrid design. Endfire radiations have been obtained\nwith a beam width of less than 25 Degree through the proposed hybrid design with an efficiency of about\n96 percent....
We discuss here under which conditions a periodic line with a twist-symmetric shape can\nbe replaced by an equivalent non-twist symmetric structure having the same dispersive behavior.\nTo this aim, we explain the effect of twist symmetry in terms of coupling among adjacent cells through\nhigher-order waveguide modes. We use several waveguide modes to accurately derive the dispersion\ndiagram of a line through a multimodal transmission matrix. With this method, we can calculate\nboth the phase and attenuation constants of Bloch modes, both in shielded and open structures.\nIn addition, we use the higher symmetry of these structures to further reduce the computational cost\nby restricting the analysis to a subunit cell of the structure instead of the entire unit cell. We confirm\nthe validity of our analysis by comparing our results with those of a commercial software....
The aim of this paper is to present and experimentally verify the first prototype of a microwave imaging system specifically designed\nand realized for the continuous monitoring of patients affected by brain stroke, immediately after its onset and diagnosis. The\ndevice is a 2D version of the 3D system, currently under construction, and consists of an array of 12 printed monopole antennas\nconnected to a two-port vector network analyzer through a switching matrix so that each antenna can act as a transmitter or\nreceiver, thereby allowing the acquisition of the entire multistatic multiview scattering matrix required for the imaging. The\nsystem has been experimentally tested on 2D phantoms with electric properties mimicking the brain. The presence and the\nevolution of the stroke have been reproduced by filling a proper cavity in the phantom with a liquid having the electric\nproperties of blood. A differential approach has been adopted by acquiring the scattering matrix before and after the filling of\nthe blood cavity. The so achieved differential dataset has been processed by means of a linear imaging algorithm in order to\nreconstruct the stroke location and dimension. Moreover, the effect of pre- and postprocessing operations on the measured data\nis investigated. A good agreement has been obtained between the reconstructions and the actual scenario. As a final remark, it is\nworth noting that the entire data acquisition and processing are sufficiently fast to allow a real-time monitoring....
An increasing number of practical applications of three-dimensional microwave imaging require accurate and efficient inversion\ntechniques. In this context, a full-wave 3D inverse-scattering method, aimed at characterizing dielectric targets, is described in\nthis paper. In particular, the inversion approach has a Newton-based structure, in which the internal linear solver is a conjugate\ngradient-like algorithm in lp spaces. The presented results, which include the inversion of both numerical and experimental\nscattered-field data obtained in the presence of homogeneous and in homogeneous targets, validate the reconstruction\ncapabilities of the proposed technique....
Loading....