Study On The Phased Array Antenna For Space-borne Synthetic Aperture Radar

Large scale active phased array antenna is one of the key components of advanced space-borne synthetic aperture radar and significantly determines the overall performance of SAR.Conventional phased arrays for space-borne SAR were mainly implemented via periodic array scheme.Those antennas have been widely employed in current space-borne SAR missions since they exhibit good pattern control ability,sufficient element failure tolerance and are easy to be implemented with well-developed design methods.However,current periodic-based phased array antenna for space SAR also suffers from large mass and volume,extremely high cost and relative low transmit to receive power efficiency since the antenna has to fulfill a series of strict space-borne SAR radiation pattern requirements including beam width,gain,ambiguity ratio,actual receiving power and so on.Those drawbacks are not favor for the developing of next generation advanced space-SAR systems.Aperiodic phased array antennas possess potentials to overcome or improve these shortcomings yet have not been comprehensively studied.In this thesis the feasibility and implement approaches of deploying aperiodic phased array antennas onto space-borne SAR are studied in a systematic and comprehensive manner,from analytical analysis to full scale EM simulation and finally hardware experiments.The key works presents in this thesis including:1.An executive and flexible space-borne SAR transmit and receive pattern design method which consists of adaptive pattern mask planning and Particle Swarm Optimization based arbitrary array synthesis is introduced.This design method aims at suppressing the ambiguity ratio while maximize the actual receiving power.The proposed design method is successfully used to generate sets of patterns for typical space SAR operating senses and modes.The design results satisfied all the space SAR pattern requirements.2.To solve the problem of relative low Transmit-to-Receive Power Transition Efficiency of current space-borne SAR phased array antenna which is mainly caused by the widely adopted ?Equal amplitude Transmit,Tapered amplitude Receive' pattern configuration scheme,a quasi-optimal high power transition efficiency pattern configuration scheme is proposed and studied,in which the normalized transmit and receive pattern are identical to each other.It is proved by simulation that the power transition efficiency of antenna based on proposed scheme is about 19% ?81% higher than the conventional results,depending on specific SAR operating sense and mode.3.The feasibility and implement approach of applying unique amplitude excitation array synthesis for various patterns which fit for different space-borne SAR operation sense and modes are studied.A concise and effective weighed averaging-based excitation merging algorithm are proposed and utilized to generate a set of excitations for different space SAR sense and modes with unique amplitude.The obtained unique amplitude excitation would function as the start point of the design of aperiodic array.Since this set of unique amplitude excitation is not exactly identical to any particular excitation for given SAR sense,the performance of corresponding patterns would degrade to some extent.Therefore,one of the key considerations in the merging algorithm is to minimize the pattern distortion for all the sense.4.Utilizing classical density taper method,the design of proposed aperiodic phased array,which corresponding to the range patterns of space-borne SAR,are carried out according to pre-obtained unique amplitude excitation of periodic array.Full wave simulation is conducted to verify the validity of the design results.Since the mutual coupling effect of aperiodic array are much more complicated than those of the periodic array,the pattern performance of one aperiodic array,which is designed with the same method for periodic array,might degrade to an unacceptable extent.However,study shows that a phase refinement could help improve the aperiodic array synthesis results so that meet the requirements of space-borne SAR.Final design performance evaluation shows that,with the restrict of maximum elements' excitation amplitude,the proposed aperiodic array exhibits similar actual receive power compare to the reference periodic array while the transmit to receive power transition efficiency increased by 63%?144%.If released from the maximum excitation amplitude constraint,the proposed aperiodic array would exhibit advantages in both actual receive power and power transition efficiency.