Channel Mismatching in Sidelobe Canceler: Limitations and Remedies

After a brief recall of the Sidelobe Canceler (SLC) working principle, including the derivation of a general formula for the Cancellation Ratio (CR), the effects of channel mismatching are investigated. In particular, curves providing CRvalues as a function of amplitude and phase channel mismatching, radar bandwidth, and jammer direction of arrival (JDOA) are provided for the cases of one and two auxiliary antennas. Subsequently, a time -space processor for performance restoration is analyzed in detail. In addition to the above mentioned quantities, the attainable CR value is expressed as a function of the space-time processor parameters. The contribution of the paper is related to the derivation of a number of mathematical equations of CR for several cases of practical interest for the radar engineer. In addition, several curves are presented to assist design of SLC systems.     

未来十年的全球水源状况

1940年至1980年间,全球的用水量翻了一番,预计到2000年还要再翻一番。由于生活水平的差异,每人每天的生活用水量也相差甚大,为20～500升。全世界有4％的人均日用水量达300～400升(美国为580升),而全世界67％的人口(主要集中在非洲和亚洲)人均日用水量小于50升。时至今日,全球范围内,仍有65％的农村人口,35％的城市人口没有供水系统。尽管如此,在过去的10年里,又有13亿人喝上了卫生的水。但是,在现在52亿的世界人口中,仍有约12亿人喝不上卫生的水。     

钢筋混凝土连续箱梁温度收缩应力计算

提出了钢筋混凝土连续箱梁温度收缩应力计算的一种模式,并对这种计算模式作了详细阐述,为工程技术人员采取适当工艺和养护方法来控制混凝土早期裂缝的发生提供了一种依据.     

气候变迁、适应能力及其发展

政府间小组委员会(IPCC)提供的第三次有关气候变化评估报告，强有力的说明了由人类诱发的气候变迁正在发生，而且世界上所有的国家都将会受到影响。