Design Of Radio Astronomy Observation Antenna On The Far Side Of The Moon

This paper focuses on the design of observation antennas for the "Hongmeng Project",which aims to observe the cosmic 21CM signal on the far side of the moon.The cosmic 21CM signal is a key indicator of the early evolution history of the universe.In order to achieve higher precision observation,some scholars proposed to move the conventional observation site from the ground to the far side of the moon,where the interference from the earth and the sun can be avoided.The main research contents of this paper include the following aspects:Non-frequency-varying antenna on lunar orbit satellite.The 21CM signal is extremely weak,and it is challenging to distinguish it from the cosmic microwave background radiation that is about 5 orders of magnitude higher.Therefore,it is necessary to impose strict requirements on the performance of the front-end observation equipment,namely the receiving antenna,mainly in terms of non-frequency-varying radiation pattern and smooth reflection efficiency,we choose the design of electric mini-antenna after comprehensive consideration.Moreover,in the high-cost observation experiment,it is very meaningful to study how to improve the reflection efficiency of the antenna and thus reduce the observation time.In the early stage of this paper,we carried out a simple application discussion on the broadband technology of electrically small antennas,including matching network and antenna loading technology.In order to avoid introducing noise,we used passive and lossless components,but the results showed that it was difficult to achieve broadband matching of electrically small antennas by loading passive and lossless components.Later,in order to achieve better impedance performance,we proposed a curved profile asymmetric double cone antenna design scheme,which had a very wide bandwidth range and good pattern performance.Its |S11| was less than-10dB within 59-925MHz close to 16 times frequency range.Within 30-120MHz,the-3dB beam width variation of the pattern was less than 8°,and the performance met the observation requirements,but it was rejected by the satellite side because of its large volume.Finally,we designed a spherical crown-shaped cone antenna with a loaded sleeve,which had smooth reflection efficiency and excellent non-frequency-varying performance.Its |S11| was less than-10dB within 77-138MHz.The-3dB beam width variation of the pattern was less than 3.3°.Then we performed a precise simulation analysis of its performance in the lunar orbit vacuum scenario,and considered the impact of satellite exposed device size on non-frequency-varying performance.After making a prototype,due to the difficulty of testing antenna performance in ultra-short wave band observation,we only performed |S11| measurement.Active electrically small film antenna on lunar backside.For lunar-based lowfrequency radio astronomy observation,this paper proposes an electrically small film antenna design scheme with active matching for low-frequency observation on lunar backside.It adopts non-Foster matching circuit,which greatly reduces the physical size of the antenna,making it lightweight and easy to deploy on lunar surface.First,we designed an electrically small film antenna that is lightweight,high-temperature resistant,easy to stretch,foldable and easy to deploy on lunar surface.Then we designed two floatingground-type non-Foster matching circuits for it by simulation.Its |S11| was greatly improved from less than-2dB overall to less than-10dB within the entire frequency band.Finally,we made a prototype and performed noise measurement.The noise power density level was less than-150dBm/Hz in most frequency ranges,which preliminarily confirmed the feasibility of the design scheme.