Spectrum analyzer

About: Spectrum analyzer is a research topic. Over the lifetime, 12217 publications have been published within this topic receiving 101851 citations.

Frequency-response characteristics of a perfect lens masked by polarizing devices

Abstract: The imaging characteristics of a perfect lens partially masked by a linear polarizer can be varied continuously either by rotating an analyzer placed at the output side or by changing the state of polarization of the input beam. In this paper we study the frequency-response characteristics and the point-spread function of such a system. It is also shown that the proposed system can be adapted either for apodization or for superresolution simply by rotating the analyzer. The fact that the unpredictable phase introduced by the mask has no harmful effect on the performance of the system makes it convenient for several applications. Expressions are obtained for the optical transfer function and the point-spread function of such a system. Some specific cases are illustrated graphically, and some probable applications are discussed.

Support Vector Machine based Differential Pulse-width Pair Brillouin Optical Time Domain Analyzer

Abstract: Support vector machine (SVM) based differential pulse-width pair Brillouin optical time domain analyzer (DPP-BOTDA) has been proposed and experimentally demonstrated. With only one SVM model, temperature distribution along 5 km fiber under test has been successfully extracted from differential Brillouin gain spectrum (BGS) measured under different spatial resolution in DPP-BOTDA. The temperature accuracy by SVM is better than that by Lorentzian curve fitting (LCF), especially when the pump pulse width difference and the number of trace averaging used in the measurement are small, indicating larger tolerance of SVM to high spatial resolution and low signal-to-noise ratio. SVM is also more robust to a wide range of frequency scanning steps and has less accuracy degradation under large frequency scanning step. To extract temperature from 50 000 differential BGSs, 133.17 and 1.12 s are consumed by SVM-0.1 and SVM-1 °C, respectively, both of which are much shorter than that by LCF. The data processing time of SVM is further shortened with the help of principle component analysis for data dimension reduction. SVM for measurand extraction would be especially helpful in the scenario of DPP-BOTDA where high data sampling rate is required to resolve plenty of submeter scale sensing points.

Optimization of the Herzog correction in the hemispherical deflector analyzer

Abstract: The theoretical performance of the hemispherical deflector analyzer has been discussed on the basis of a numerical calculation of electron trajectories by taking the fringing field correctly into account. We optimized both the ‘‘Herzog region’’ and the electrode sector angle and got foci of electrons which are as good as those for the ideal‐field 180 ° analyzer. In the optimized analyzer, even electrons with their energies different from the pass energy are focused well at the exit plate. Moreover, the arriving position of electrons at the exit plate depends linearly upon their incidence energy. The possibility of using a position‐sensitive detector is discussed.

Device for measuring linewidth of narrow linewidth laser based on optical fiber time-delay self heterodyne method as well as method for measuring thereof

Abstract: The invention discloses a device of measuring the line-width of a laser with narrow line-width and a method of measuring the line-width based on a optical fiber delay self-heterodyne method; in the hardware device, an optical fiber delay line is connected between a first and a second couplers; an acousto-optic modulator is connected between the first and the second couplers; the measured laser is connected to the input of the first coupler, and a photoelectric detector is connected to the output of the second coupler; the photoelectric detector is connected with a spectrum analyzer. In the line-width measurement, simulation models of the line-width triangle aE of the laser and the spectrum-width triangle f of the photoelectric current heterodyne signal are built in the frequency shift delay self-heterodyne methodology, and the function relation between the line-width triangle aE of the laser and the spectrum-width triangle f of the photoelectric current heterodyne signal is obtained fitting of the three-level proportion function model. The invention presents that with the short optical fiber delay self-heterodyne method, the device can eliminate the deficiency of greatly reduced measuring precision because of not enough delayed time in the delay self-heterodyne method when the length of the delay optical fiber is less than 6 times coherence length of the laser, so as to provide an effective method of precisely measuring the line-width of the laser with narrow line-width in projects.

Propagation comparisons at VHF and UHF frequencies

Abstract: This paper presents and compares measured propagation data taken at four unlicensed-band frequencies including 151MHz, 433MHz, 902MHz and 2400MHz. A custom 10mW signal source was used as the transmitter, and a spectrum analyzer as the receiver to provide accuracy to within 1dB and sensitivity to better than −120 dBm. Both monopole and low-gain directional antennas were employed to represent expected use in an Energy Harvesting application. The measurement environment included both indoor and outdoor features. A range of up to 1.5km at the lower frequencies was achieved. The path-loss exponent was found to be approximately three to five and relatively independent of the operating band. Results confirm that lower frequencies are preferred for low-power applications when omni-directional and low gain antennas are used.