Current Issue : July - September Volume : 2012 Issue Number : 3 Articles : 6 Articles
An ultra-wideband (UWB) modified 3-way Bagley polygon power divider (BPD) that operates over a frequency range of 2ââ?¬â??16 GHz\r\nis presented. To achieve theUWBoperation, the conventional quarter-wave transformers in the BPD are substituted by two tapered\r\nline transformers. For verification purposes, the proposed divider is simulated, fabricated, and measured. The agreement between\r\nthe full-wave simulation results and the measurement ones validates the design procedure....
Passive components, such as microstrip power couplers, operating in microwave spectrum-regime can be considered as absolute energy eaters because they reduce the overall system throughput. The compatible 3-D volumetric design related issues resulting into undesired qualitative energy and power losses are of major concern for designers. Naturally available conventional double positive dielectric (DPS) materials such as FR-4, PTFE, and Teflon have been popularly used as substrates on the cost of deteriorating the overall electrical performance of transceiver systems. These DPS materials have both the dielectric permittivity (ε) and magnetic permeability (µ) positive. The recent RF and wireless communication industry demands the symmetric and asymmetric microstrip forward and backward impedance couplers designed on the principle of novel left-handed electromagnetic materials. These metamaterials observe unique electromagnetic properties of having the ε and/or µ less than zero simultaneously that replace those having been designed using DPS. This paper discusses and investigates the novel concept for the methodological improvements to various measurable parameters like S-parameters, coupling _bandwidth and _ratio, multi frequency response, and volumetric miniaturization for these couplers. It can be achieved through the introduction of Split Ring Resonator (SRR) and rod structure in thin slab of naturally available DPS substrate. Mechanical design issues such as 2-D alignment and orientation, dimensions, spacing between SRRs and rods, number and size of unit cells, and structural-materialistic properties deciding the electrical characteristics of the metamaterial and the coupler responses are focused. Mathematical justifications and logical concepts through numerical modeling carried out by various researchers have been highlighted and studied here....
The effects of adaptive genetic algorithms (AGAs) and defected ground structures (DGSs) on performance optimization of tapered\r\nmicrostrip filter are investigated. The proposed structure achieves an ultra wide stopband with high attenuation within a small\r\nsurface area, as well as 45% smaller size, in comparison with conventional filters. The parameters of the filter are optimized using\r\nin-home AGA code. In the proposed AGA algorithm, the crossover and mutation probabilities are adaptively changed according\r\nto the value of individual fitness. Then by utilizing the proposed DGS, a compact S-band lowpass filter with ultra-wide spurious\r\nfree window is obtained. The proposed filter achieves an insertion loss of 0.8 dB from DC up to 4 GHz and 21 dB rejection in the\r\nstopband from 4.3 up to 60 GHz. The fabricated and measured results exhibit good agreement with the simulated results. They\r\ndemonstrate that combining AGA and DGS yields best possible response for this group of filters....
A nonuniformly spaced linear antenna array with broadside radiation characteristics is synthesized using firefly algorithm and\r\nparticle swarm optimization. The objective of the work is to find the optimum spacing between the radiating antenna elements\r\nwhich will create a predefined arbitrary radiation pattern. The excitation amplitudes of all the antenna elements are assumed to be\r\nconstant. The optimum spacing between the array elements are obtained using firefly algorithm. The minimum allowed distance\r\nbetween the antenna elements is defined in such a way that mutual coupling between the elements can be ignored. Numerical\r\nanalysis is performed to calculate the far-field radiation characteristics of the array. Two numerical examples are shown to form\r\ntwo different desired predefined radiation patterns. The performance of the firefly algorithm and particle swarm optimization is\r\ncompared in terms of convergence rate and global best solution achieved. The performances of the optimized nonuniformly spaced\r\narrays are analyzed. Finally, contour plots of the radiated power fromthe optimized array in the horizontal plane and vertical plane\r\nin the far-field region are provided....
An effective solution to reduce both the mutual coupling and return loss of a microstrip array antenna consisting of rectangular\r\npatches is proposed. The patch is made concave in both horizontal and vertical sides. Applying the proposed structure to a\r\nmicrostrip array antenna having two elements, the effects of patch concavity on the mutual coupling and return loss are simulated\r\nand studied. To obtain a concave rectangular patch array antenna having low amounts of mutual coupling and return loss, the\r\npatch length and width as well as the amounts of concavities are optimized using an enhanced genetic algorithm. To verify the\r\nsimulation results, then, the optimal array antenna is fabricated. The simulation and experimental results confirm that the optimal\r\nconcave rectangular array antenna has low amounts of mutual coupling and return loss....
The effects of substrate materials on the design of microstrip power divider are investigated theoretically and experimentally. Three\r\ndielectric substrate materials, Duroid 3003, G10/FR4 epoxy Glass, and Duroid 3010, are chosen to be studied. A three-way twostage\r\npower divider is designed at S-band frequency of 2.25 GHz and etched on each studied substrate separately. The substrate\r\neffects on the characteristics and performance of the microsrip circuits are studied taking into consideration the large difference in\r\ndielectric constant and the dissipation factor. The circuit designs presented here are analyzed using the Genesys CAD program and\r\nimplemented and tested experimentally. The simulated and measured results are compared and discussed, and they indicate that\r\nsignificant changes in the characteristics of the microstrip power divider are observed....
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