tends to be sensitive to the tolerances in both the design and fabrication, some related sensitivity analyses based on the proposed parameters have been performed, and it is found that the tuning distortion caused by the variation of resonant frequency of each resonator have some noticeable effect on the desired response. CONCLUSIONThis letter presents the synthesis of a narrow-band bandpass filter for CDMA2000 communications systems, which has a 14pole general Chebyshev function response with a passband of 11.2 MHz at 830 MHz. The coupling matrix of the filter is derived from cost function using nonlinear LM algorithm. The filter response with two pairs of TZs for group delay self-equalization and one pair of TZs at finite frequencies for high selectivity requirement is implemented by using three CQ coupling structures. The frequency responses demonstrating a good agreement between the measured and the simulated specifications are obtained. The proposed method can be further exploited for various mobile communication system applications.
We report an enhanced experimental set-up that allows fast and accurate determination of refractive indexes in optical materials. The set-up is equipped with the high-precision sample positioning system and sensitive detector for the registration of interference fringes shift. Additionally, an approach that can be utilized in order to eliminate the error caused by non-parallel sample edges is discussed. The results of the refraction index measurements in lithium niobate are presented.Refractive index for a given wavelength is a crucial parameter for optical media. Although, there exists a variety of methods that allow determining the refractive index of the given material [1, 2, 3], iterferometric-tuming technique [4] has several advantages in compare to other methods. One of the main arguments in favor of iterferometric-turning measurements scheme is the possibility of fast, non-destructive and accurate analysis of the particular crystalline sample that is prepared for further use in different applications.In this report we describe the improved implementation of the interferometric-turning technique. The essential goal of the improved design was to achieve higher precision of the rotation angle and eliminate the errors related to sample geometry.Block-diagram of the experimental automated set-up for the measurements of refractive indices is shown in Fig. 1. Light beam from the laser 1 is split in two by the semitransparent prism 2. One of the beams then travels through the reference arm of the interferometer and is reflected from the mirror 3.The other one passes through the polarizer 5 and the sample 11. Then, after being reflected from the mirror 4, it travels back again through the sample. Eventually, both beams interfere at the photo detector 7 (the lens 6 is used for focusing purposes).Computer lOis employed for the communication with the analog-to-digital converter module 9.1 and step-motor control unit 9.2 that drives the rotational table 8. The measurement idea is the following. Sample is rotated from the initial position (tp= O ) by the angle cp. Considering the sample thickness as d, the laser wavelength as A (in our case A=633 nm) and the number of interference maxima for which the fringe is shifted [5] one obtains the refractive index n [4]: n = sin 2 tp + (1-costp -K2/ 2d)2 (1) 2(1 -cos tp -K2/ 2d) When the refractive index of the medium, in which the sample is placed, is taken into account, the working formula is [6]: sin 2 tp·n� + [(1-costp) . ne -K2/2d]2 n = 2[(1-cos tp) . ne -K2 / 2d]As it is clear from the expressions (1) and (2), the accuracy of the refractive index determination is directly connected to the precision of the rotation angle. Therefore, one of the primary goals during the set-up modernization was to design high precision computer-controlled sample positioning system.
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