when just using the method of CDA. The result shows that the maximum strain variation is about 9.4 and the resolution is about 5.7 , which is better than the direct peak detection. In order to enhance the resolution of the system, two 201 st -order digital low-pass FIR filters with cutoff frequency of 10 Hz are applied on the detected scanning voltage and PD signal, respectively, to remove the high-frequency noise and improve the signalto-noise ratio (SNR). Then the CDA method, which has the effect of averaging, is used to determine the peak signal. The maximum strain variation is 2.2 and the resolution is 1.39 , which are better than just using the CDA method, are shown in Figure 3(c). Comparing the results of Figures 3(a), 3(b), and 3(c), we can conclude that by combining the CDA and digital FIR filter, the resolution of the demodulation system is greatly enhanced. In order to verify the effectiveness of the technique, a series of stepped strains with step size of 36 and time interval of 2.5 s are applied on the FBG sensor. The experiment results are shown in Figures 4(a) and 4(b). It is clearly observed that with FIR and CDA, the measured strains are more resoluble than that of the method without FIR and CDA. CONCLUSIONIn conclusion, a fiber Bragg grating (FBG) strain-sensor demodulation system based on a wavelength-tunable fiber-ring laser has been developed. By using the digital FIR filter to improve the SNR and CDA peak-detection algorithm, the resolution of the strain system was greatly improved. An enhanced strain resolution of 1.39 was achieved, which is much better than the resolution (10.1 ) of the direct peak-detection method. resolution, wavelength-division multiplexed in-fiber Bragg grating sensor system, IEEE Electron Lett 32 (1996), 924. 4. M.G. Xu, H. Geiger, and J.P. Dakin, Modeling and performance analysis of a fiber Bragg grating interrogation system using an acoustooptic tunable filter,
design and also in fabrication, the resultant CP is not pure, corresponding a finite cross-polar level.The simulated and measured radiation patterns are shown in Figure 5. For the designed sample, the measured results of Ϫ26-dB cross-polar level, Ϫ13-dB side-lobe level, ϳ13.5°half-power beamwidth, and 17.3-dBi gain corresponding to ϳ40% aperture efficiency are obtained. The bandwidth for cross-polar level less than Ϫ15 dB excesses 8%. Hence, the precise polarized variability by adjusting and ␣ in a relatively broad band can be expected. CONCLUSIONIn this paper, a novel broadband reflectarray with variable polarization has been proposed, and the principle of polarized variability has been analyzed in detail and also verified by simulation and experiment. The mechanism of polarized variability is quite simpler than a traditional antenna with complex feed network; only the operation of mechanical rotation is needed. This reflectarray presents good features of broadband and higher gain (with a great number of elements), and has potential significance for engineering application.ABSTRACT: The miniaturization of hairpin lowpass filters by employing two high-permittivity ceramic substrates (with respective dielectric constants of 9.7 and 22.6) are investigated. Microwave dielectric ceramics with high permittivity are commonly applied in several microwave communication components. With the advantages of compact size, high-permittivity ceramics can be used as the substrate for low-pass filters. Moreover, the fundamental characteristics of newly developed compact stepped-impedance hairpin resonators with parallel coupled lines have also been described and applied to the design of lowpass filters. In this paper, the designed multiple cascaded stepped-impedance hairpin resonators structures are simulated using an IE3D simulator. The responses of the fabricated filters using Al 2 O 3 ( r ϭ 9.7, Q ϫ f ϭ 350,000 GHz) and 0.2 Ca 0.6 La 0.26 TiO 3 -0.8Mg 0.95 Co 0.05 TiO 3 ( r ϭ 22.6, Q ϫ f ϭ 57,000 GHz) ceramic substrates are designed at a cutoff frequency of 1.8 GHz. This compact, low-loss, sharp cutoff-frequency response, and broad-stopband lowpass filter should be useful in many wireless communication systems.ABSTRACT: In this paper, chirped fiber Bragg gratings (CFBGs) are proposed as signal-phase controllers for microwave-photonic wireless downstream fiber links. The effect of high-order modulation optical sidebands that disturbs the output mm-wave signal due to the chromatic dispersion induced by the gratings is studied theoretically and experimentally. The 1 st and 2 nd mm-wave harmonics of the output signal have been measured for conventional intensity modulation and for intensity modulation with optical carrier suppression. In the last case, data transmission at 2.5 Gb/s is demonstrated through a chirped grating of 280 ps/nm dispersion in a 40-GHz modulated link.
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