Microwave holography of large reflector antennas--Simulation algorithms

Abstract

The performance of large reflector antennas can be improved by identifying the location and amount of their surface distortions and then by correcting them. Microwave holography techniqnes are finding considerable applications as viable tools for performing this task.In these techniques, the complex (amplitude and phase) far-field pattern of the antenna is measured, using a reference antenna. Then, the Fourier transform relationship, which exists between the far field and a function related to the induced current, is invoked to result in the identification of the surface distortions.To critically examine the accuracy of the constructed surface profiles, simulation studies are required to incorporate both the effects of systematic and random distortions, particularly the effects of the displaced surface panels.In this paper, different simulation models are investigated with emphasis given to a model based on the vector diffraction analysis of a curved refleetor with displaced panels. The simulated far-field patterns are then used to reconstruct the location and amount of displacement of the surface panels by employing a fast Fourier transform (FFT)/iterative procedure. The sensitivity of the microwave holography technique based on the number of far-field sampled points, level of distortions, polarizations, illumination tapers, etc., is also examined. In addition, the relationships between Az-El and uu spaces are addressed in the Appendix. Most of the data are tailored to the dimensions of the NASAIJPL Deep Space Network (DSN) 64-m reflector antennas for which the result of a recent measurement is also presented.

A Multi Facets Composite Panel Reflectarray Antenna for a Space Contoured Beam Antenna in Ku Band

“…RF diagnosis techniques have been proposed to reconstruct the near field over a radiating aperture [26]. The phase shift of the reflectarray elements can thus be reconstructed.…”

Effect of Facet Displacement on Radiation Field and Its Application for Panel Adjustment of Large Reflector Antenna

“…BEN-NETT, et al [10] presented a sufficiently detailed analysis of this method to draw the attention of radio astronomers. SCOTT and RYLE [11] used the new Cambridge 5 km array to measure the shape of four of the eight antennas, using a celestial radio point source and the remaining antennas to provide the reference signal Simulation algorithms were developed by RAHMAT-SAMII [12] and others [13][14][15][16], adding to the practicability of the method. Using the giant water vapour maser at 22 GHz in Orion as a source, MOR-RIS, et al [17] achieved a measurement accuracy of 30 microns and were set the surface of the IRAM 30 m millimeter telescope to an accuracy of better than 100 microns.…”

Applications of the diagnosis techniques in antenna for the reduction of the measurements errors

“…With this information, it is possible to detect errors, and also to identify which are the causes of such errors, for example, electrical errors in arrays or mechanical errors in reflectors. These classical applications have been widely studied in applications [1]- [2]. The presence of these errors affects to the far field pattern but, often these errors are very difficult to be detected from this pattern.…”