| Rain drop size distribution plays an important role in precipitation research,microwave detection of rain drop size distribution is mainly based on radar.Precipitation effects on scattering,absorption and attenuation of emitted microwave signals.The rain drop size distribution in the detection area can be retrieved by using the backscattering echo power spectrum of precipitation particles.Based on the distribution characteristics of rain drop size distribution,this paper analyzes the requirements of precipitation radar antenna for detecting rain drop size distribution of different intensity precipitation,and designs a biasfeeding reflector antenna to cooperate with the microwave trittansming and receiving system for raindrop spectrum detection.The research and design are carried out in the following aspects.Firstly,according to the distribution characteristics of raindrop spectrum and the sensitivity of the receiver,the influence of antenna performance on precipitation detection capability is discussed.The antenna gain index should be over 40 dB to identify precipitation particles with height within 10 km,especially for weak precipitation.Taking the precipitation radar antenna as a reference,in order to avoid the influence of the vertical pointing antenna water accumulation on the echo and reduce the occlusion of the feed to the reflector,the design of the offset-feeding reflector antenna is determined to achieve the purpose of high gain and low sidelobe level.Secondly,the feed is mainly designed in two aspects.One is the cone-shaped axial corrugated horn feed.The standing wave ratio is lower than 1.5,the gain reaches 15 dB,the sidelobe level reaches-26 dB,and the cross polarization is low.The second is at the corner.On the basis of the cone horn,the radiation boundary of the standard pyramid horn is changed,and the beam is shaped by the Gaussian curve to achieve a gain of 15.8 dB,the standing wave ratio is lower than 1.2,and the 3 dB beamwidth is 30°,and the radiation of E-plane and H-plane is similar.The deviation of phase center is small.Meet the design specifications of the feed.Thirdly,according to the equation of parabolic reflector to design the reflector,and the influence of the focal length ratio in the corresponding range is compared according to the opening angle within the tapering level of-10 dB.The ratio of focal length to the effective diameter is chosen to be 0.65,and the gain and edge illumination level of the reflector antenna are optimal.When the ratio of focal length to the effective diameter is determined,compare the influence of the aperture size of the 0.6m and 0.75 m reflector.The geometric parameters of the parabolic reflector are determined to achieve a gain of 40 dB,a beamwidth angle of 1.5°,and a sidelobe level of less than-30 dB,which is the design index of the microwave raindrop spectrometer antenna.Based on the theoretical research,this paper combines the simulation software to realize the joint simulation of the feed and the reflector,and verifies that the designed antenna has the performance indexes such as gain,standing wave ratio,beamwidth,sidelobe level and cross polarization in the frequency range meet the design requirements. |
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