Abstract-An investigation of the Ewald method is presented. The method involves a splitting parameter that is theoretically an arbitrary number. An analysis is presented to show why the splitting parameter cannot always be treated as arbitrary in calculations and how this parameter should be chosen for all periodic spacing of a structure.
proposed antenna, probe feeding and an air gap (capacitive gap) were used. Simulations were conducted to optimize the lengths of the probe and air gap in order to obtain the widest bandwidth in terms of return loss (VSWR [lt] 2) at 2 GHz band. According to the measured results for the antenna implemented, the impedance bandwidth was 734 MHz (29.01%) ranging from 2.163 to 2.897 GHz and the axial ratio bandwidth (AR [lt] 3dB) was 135 MHz (5.48%) ranging from 2.394 to 2.529 GHz. The CP characteristic of the antenna can be applied to mobile applications for the 2.4 GHz WLAN. [3][4][5][6][7][8][9][10][11][12][13][14]. Generally, the properties of the fractal geometry are related with the electromagnetic behavior of the antennas. As for the Koch fractal dipole antenna, if the heights of the antennas are fixed and the number of iterations is increased the resonant frequency of the antennas decreases. Decreasing the resonant frequency with fixed height has the same effect as miniaturizing the antenna at a fixed resonant frequency. In addition to the miniaturization effect, using fractals improves the antenna parameters, making them suitable for many applications. Most of the fractal antennas can also be used as multiband and wideband antennas because of the self-similar property of the geometry. Sierpinski antenna is one of those which can be used to achieve similar radiation patterns at various operating frequency bands.When small and multiband antennas are considered, fractal trees are also very good candidates [15,16]. They are widely used in the design of miniaturized antennas because of their space filling ability, compact size, and multiband behavior. Three dimensional fractal trees with self-similar branch structure are also examined in [17,18]. Fractal tree antennas are designed by using various scale factors [19] but the length ratios of consecutive branches are constant. In this study, the antennas with nonuniform branch length ratios are proposed and investigated. The new antennas are compared with the ones designed by using uniform length ratios in terms of the fundamental antenna parameters. The antennas are also fabricated and measured. ANTENNA DESIGNFractal tree antennas generated by applying an iterative procedure are obtained by using a constant scale factor and this factor in the designs is generally chosen as 1/2. Therefore, the branch lengths increases according to the number sequence 1, 2, 4, 8, 16, 32, . . . from the tip of the antenna to its base. Since the length of the following branch is the double of the previous one, the antenna is called as the D version in this work. The new antenna whose branch length ratios are not constant is designed similar to the D version but its branch lengths increases according to the Fibonacci number sequence from the tip to the base. The Fibonacci numbers appear in many unexpected places in nature such as on flowers, plants, and trees [20]. Therefore, in this study, it is intended to use this special sequence for the generation of fractal trees. The Fibonacci...
Abstract-In this letter, a log-periodic dipole array (LPDA) antenna operating between 1.1 and 13.8 GHz with and an average peak realized gain of 5.2 dB is presented. It is suitable for GPS (L1-L5), PCS, IMT-2000, Bluetooth, WLAN, WiMAX, UWB, and X-band applications. The antenna is designed by introducing a subsectional tapered feedline instead of standard microstrip feeding, which leads to a remarkable lower-frequency performance. The upper-frequency performance of the antenna is improved by adding a feeding point patch. The group delay is also examined for the final design, and maximum 1.5 ns deviation is observed in UWB. By using ordinary and simple dipoles with this modified feedline approach, a superior antenna performance is obtained over a very wide frequency band, and it is validated by the comparison of three fabricated antennas. Additionally, the antenna size is also reduced without using complicated and/or top-loaded dipole structures.Index Terms-Feeding point patch, printed log-periodic dipole array antenna, subsectional tapered feeding.
In this letter, multi-band coplanar waveguide (CPW) fed multiple-input-multiple-output (MIMO) antenna is presented for Bluetooth, WLAN and WiMAX applications. The elements of MIMO antenna are identical CPW-fed printed monopole antennas whose bandwidth performances are improved by employing inverse U and meander line slots. In the design of the antennas, a low-cost FR4 substrate is used and the size of the element antennas are optimized as 35 mm x 30 mm. According to the measurements, S 11 is below 210 dB in 2.38 GHz -2.52 GHz and 3.19 GHz -6.44 GHz bands with 0.2 dB and 2.9 dB average peak realized gains, respectively. The element antennas are placed orthogonally and fed independently to obtain MIMO structure whose size is optimized as 42 mm x 62 mm. The performance of MIMO antenna is also examined in terms of diversity parameters such as envelope correlation coefficient and apparent diversity gain, which are lower than 0.02 and higher than 9.9 in the operating bands, respectively.
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