The deformation of reflector surface can be obtained by misell algorithm using two far-field amplitude patterns: one with the antenna in focus and the other with the antenna defocused. For reflector antennas with acti...
详细信息
The deformation of reflector surface can be obtained by misell algorithm using two far-field amplitude patterns: one with the antenna in focus and the other with the antenna defocused. For reflector antennas with active surface, the defocused pattern can be measured by adjusting the panels to get a more effective phase factor instead of offsetting the sub-reflector. The shape and size of phase factor have a great influence on the accuracy of convergent solution. To improve the performance of misell algorithm, this study proposed an optimisation method for phase factors under different surface deformations. This method utilises Levenberg-Marquardt algorithm to get an estimation of the aperture distribution and then applies the particle swarm optimisation to optimise the phase factor parameterised by Zernike polynomials. Numerical simulations show that the proposed method is an efficient tool to achieve applicable phase factors under different surface deformations. Using the optimised phase factor, misell algorithm can get a better convergent performance than traditional misell algorithm.
The misell algorithm is an effective phase-retrieval holography method for measuring the surface error of large reflector antennas. However, it is investigated experimentally to have a low accuracy at low signal-to-no...
详细信息
The misell algorithm is an effective phase-retrieval holography method for measuring the surface error of large reflector antennas. However, it is investigated experimentally to have a low accuracy at low signal-to-noise ratio (SNR). To decrease the great sensitivity to noise of misell algorithm, a new iterative Fourier filtering approach based on autocorrelation theorem is proposed. The iterative Fourier filtering approach is used to remove some of the imperfection present in far-field amplitude data. The computer simulation results of Shanghai Sheshan-25m-telescope model show that the proposed approach improved the accuracy of misell algorithm at low SNR obviously.
The quality of high performance microscope objectives is usually verified by interferometric measurement of the wave front. However, a non-interferometric method might be preferable, when appropriate light sources of ...
详细信息
ISBN:
(纸本)0819445347
The quality of high performance microscope objectives is usually verified by interferometric measurement of the wave front. However, a non-interferometric method might be preferable, when appropriate light sources of sufficient coherence length or an interferometric setup are difficult to realize. Under these circumstances, the complex pupil function of an optical system can also be determined from its intensity point spread function (PSF), i.e. from the image of a sub-resolution point object. We present a system that can determine the pupil function of high-NA microscope objectives from defocused images of an artificial point source. An extended version of the misell" algorithm is used, which utilizes 4 or more PSF images to overcome the Fourier phase ambiguity and which generally converges rapidly to the correct pupil function both in phase and amplitude. The algorithm can also compensate small errors in the x-, y- and z-positions of the images, which might be caused by vibrations, thermal drift or the limited accuracy of the z-drive.
It is shown how the principles of simulated annealing can be incorporated into the misell algorithm for phase retrieval. Simulations of phase retrieval from the infocus and defocused radiation patterns of a reflector ...
详细信息
It is shown how the principles of simulated annealing can be incorporated into the misell algorithm for phase retrieval. Simulations of phase retrieval from the infocus and defocused radiation patterns of a reflector antenna show that the solution can be refined in this way. Locking at local minima can be avoided and the accuracy limits set by the measurement errors can be reached. The price paid for a reliable and significant improvement in accuracy is at least an order of magnitude increase in computing.
This paper investigates the phase retrieval holography (PRH) method using the misell algorithm for measuring the surface error of a large reflector antenna. PRH is a technique that does not require phase measurement. ...
详细信息
This paper investigates the phase retrieval holography (PRH) method using the misell algorithm for measuring the surface error of a large reflector antenna. PRH is a technique that does not require phase measurement. The algorithm is investigated experimentally and the estimation errors are evaluated quantitatively using measurement simulation. First, it is shown that estimation errors can be reduced using an initial aperture distribution calculated by ray-tracing. The measurement resolution is improved by applying an extrapolation algorithm to the misell algorithm, Finally, the surface error of a Cassegrain antenna with an aperture of 64 m to resolution of about 4.1 m in the aperture plane was measured by receiving a test signal from a geostationary satellite (frequency: 1.545 GHz). As a result of the experiment, the surface error of 1.57 mm RMS and measurement reproducibility of 0.54 mm RMS were obtained and it was confirmed that this method is effective as a simple surface measurement method.
暂无评论