Development Of A Wideband Feed For Dark Energy Detection

The research of dark energy is the major leading-edge issue in contemporary science.The modern universe theory believes that the detection of dark energy can come true by radioobservation, that is, we can measure the large-scale structure of the universe accurately andthen identify the cosmic expansion velocity at different red shift by the baryon acousticoscillation (i.e. BAO) in the space power spectrum. The broadband feed designed in this paperis an important part of the detection method. Based on the Tianlai project proposed byChinese Academy of Sciences, the paper expores a method of the dedicated wideband feed,and develops a kind of wideband feed which electrical properties is good between400MHz to1400MHz.On the basis of comparative analysis of the antenna array and wideband feed at homeand abroad, this paper points out that the majority of current using broadband feed is between225MHz to750MHz. The symmetry of the far field radiation pattern is poor, the consumptionof echo is high and matching ability is weak. This paper introduces the principle of thereflector antenna and electromagnetic field theory, and analyzes the special index of widebandfeed in the Tianlai project, proposes a method for reducing the mutual influence of parabolicantenna and feed.According to the technical requirement of the broadband feed in the Tianlai Project, thispaper identifies a modified folded-broadband feed which is between600MHz to1400MHzand has good properties, obtains the optimal structural parameters from the simulation ofbroadband feed designed in the CST, a three-dimensional electromagnetic simulation software,develops and tests the modified folded-model machine according to the optimal structure. Theresults show that the feed developed has very good broadband properties between400MHz to1200MHz, and it can guarantee the high efficiency of the antenna array. Meanwhile, itsvoltage standing wave ratio(i.e. VSWR) is less than2.5and the band is approximately50%,all of which can meet the technical requirement of the Tianlai Project well.This paper analyzes the six meter diameter parabolic antenna, identifies its structuralparameters and the phase center of the modified folded-wideband feed, then assembles thefeed on the the parabolic antenna, and thus makes the phase center coincide with the focus ofthe parabolic antenna to guarantee the parabolic antenna can get a ideal wavefront. In theexperiment, the temperature of system can be measured by the shift between the feed and standard noise source, and the temperature is about70K. Through the observation of the radiosource of the sun, CygA, CasA and so forth, we can get good interference pattern. Bycomparing the data of phase between simulation and observation, we find the slope ofinterference fringes are totally identical. It shows a good consistency of parabolic antennasystem and the good electrical property of the broadband feed and the system.The developed wideband feed and measurement solution in this paper is beneficial to theresearch of the wideband of feed, provides the preferred solution for wideband feed of theTianlai project.