Abstract-In this paper, a low-cost multiband printed-circuit-board (PCB) antenna that employs Koch fractal geometry and tunability is demonstrated. The antenna is fabricated on a 1.6 mm-thick FR4-epoxy substrate with dimensions 4 cm × 4.5 cm, is microstrip-line fed and has a partial ground plane flushed with the feed line. The proposed antenna is simulated using the Finite-Element Method for three different switching cases and the return loss is measured for each case. It is shown that the antenna can cover the bands of several applications including 3G, WiFi, WiMAX as well as a portion of the UWB range. The radiation patterns are satisfactorily omnidirectional across the antenna's operation bands.

With the prevalence of breast cancer among women and the shortcomings of conventional techniques in detecting breast cancer at its early stages, microwave breast imaging has been an active area of research and has gained momentum over the past few years, mainly due to the advantages and improved detection rates it has to offer. To achieve this outcome, specifically designed antennas are needed to satisfy the needs of such systems where an antenna array is typically used. These antennas need to comply with several criteria to make them suitable for such applications, which most importantly include bandwidth, size, design complexity, and cost of manufacturing. Many works in the literature proposed antennas designed to meet these criteria, but no works have classified and evaluated these antennas for the use in microwave breast imaging. This paper presents a comprehensive study of the different array configurations proposed for microwave breast imaging, with a thorough investigation of the antenna elements proposed to be used with these systems, classified per antenna type, and per the improvements that concern the operational bandwidth, the size of the antenna, the radiation characteristics, and the techniques used to achieve the improvement. At the end of the investigation, a qualitative evaluation of the antenna designs is presented, providing a comparison between the investigated antennas, and determining whether a design is suitable or not to be used in antenna arrays for microwave breast imaging, based on the performance of each. An evaluation of the investigated arrays is also presented, where the advantages and limitations of each array configuration are discussed.

The perturbation of the lower hybrid wave (LH) power spectrum by fluctuations of the plasma in the vicinity of the antenna is investigated by solving the full wave equation in a slab geometry using COMSOL Multiphysics®. The numerical model whose generality allows to study the effect of various types of fluctuations, including those with short characteristic wavelengths is validated against a coupling code in quiescent regimes. When electron density fluctuations along the toroidal direction are incorporated in the dielectric tensor over a thin perturbed layer in front of the grill, the power spectrum may be strongly modified from the antenna mouth to the plasma separatrix as the LH wave propagates. The diffraction effect by density fluctuations leads to the appearance of multiple satellite lobes with randomly varying positions and the averaged perturbation is found to be maximum for the Fourier components of the fluctuating spectrum in the vicinity of the launched LH wavelength. This highlights that fast toroidal inhomogeneities with short characteristics length scales in front of the grill may change significantly the initial LH power spectrum used in coupled ray-tracing and Fokker-Planck calculations.

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