Abstract-This paper discusses the analysis of a novel two-segment rectangular dielectric resonator antenna (DRA) for broadening of the impedance bandwidth. In the proposed configuration, two rectangular dielectric sections are used which are separated by a metal plate. With this configuration, it is possible to excite two adjacent resonant frequencies. Utilizing the two-segment thin DRA and skillfully varying its aspect ratio, an appropriate structure is obtained that illustrates more than 76.8% impedance bandwidth (for S 11 >10 dB) at 3.32-7.46 GHz frequency band.

Abstract-In this paper, pattern search (PS) algorithms are introduced as a new tool for array thinning. It is shown that by selection of a fitness function which controls more than one parameter of the array pattern, and also by proper setting of weight factors in fitness function, one can achieve very good results. The method is tested on linear arrays of isotropic and non-isotropic elements and is shown to be useful in both cases. Mainlobe scanning to different angles is also tested and the results are success. In all cases studied in this paper, relative sidelobe level (SLL) is less than −20 dB with only small increase in mainlobe beamwidth compared to the case of a uniform array. Results of PS optimization are compared in two cases, which their starting points of optimization are different from each other. There is also a comparison made between results of array thinning using Genetic Algorithm (GA) and PS, and PS is shown to be a fast and reliable algorithm to be used in array thinning problem.

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Miniaturization of a rectangular microstrip antenna using a magneto-dielectric substrate is discussed theoretically and experimentally. A compact magneto-dielectric substrate is designed using a metamaterial structure which can reduce the antenna dimensions by increasing the constitutive parameters of the substrate. Furthermore, the proposed structure is thin enough to be embedded in a single dielectric substrate. The area of the microstrip antenna with the proposed magneto-dielectric substrate at 2.4GHz is reduced up to about 65% compared to a conventional dielectric microstrip antenna. The bandwidth of the miniaturized antenna is almost unchanged due to the increase of the magnetic permeability at the designed 2.4 GHz frequency. Finally a fabricated version of the miniaturized antenna is tested and measured. The results of the measurement and simulation are in good agreement.

This study investigated the microwave absorption properties of core-shell composites containing; iron oxide decorated carbon nanotubes (CNTs) and silica (SiO2@Fe3O4-MWCNTs) with various thicknesses of silica shells (7, 20 and 50 nm). Transmission electron microscopy (TEM) and X-ray diffraction results confirmed the formation of these core-shell structures. Microwave absorption characterization of the samples at the ranging band under consideration (the X-band) showed increased absorption and shifting of the peaks to lower frequencies compared to the uncoated sample (Fe3O4-MWCNTs). The minimum reflection loss decreased with increasing SiO2 thickness. The minimum reflection loss of the composite with an optimized thickness of the silica shell (7 nm) exceeded -41 dB at 8.7-9 GHz.