中频雷达利用圆极化波探测中高层大气的风场和电子密度,通过一组正交偶极子组成的空分天线阵完成圆极化波的发射和接收。由于风场和电子密度反演对回波的极化特征有不同需求,要求接收端既能为电子密度的反演保留也能为风场的反演消除回波的极化特征。目前中频雷达消除极化特征通常采用硬件来完成,接收端将正交偶极子所接收到的一路信号利用移相器进行±π/2 的相位调整后叠加到另一路信号上最终将圆极化回波还原为单路信号。但在中频频段实现相位调整是以增加器件和系统的复杂度为代价,而且器件的可靠性会受到环境的影响。本文提出一种无需硬件调相,直接利用I/Q 分量合成消除极化特征后回波的I/Q 复序列的方法,实现时仅需让接收端对信号序列逐点进行加减法运算及幅度判决。理论分析和数值仿真均表明新方法能够有效消除极化、正确获取I/Q 复序列,而且方法简单,信号合成器也易于实现,具有一定的工程实践价值。
The medium frequency radar uses the circular polarization echoes to retrieve the wind fields and the electron density in the middle and upper atmosphere. To transmit and receive circular polarization echoes, a spaced antenna system, composed of a series of cross-dipoles, is used. Different demands are imposed for the circular characteristics in the echoes to retrieving the wind fields and the electron density, consequently, the receiver should be able to keep and remove the circular characteristics in the echoes. In most medium frequency radars, a hardware solution is adopted to remove the circular characteristics by making a phase adjustment to one of the two sets of signals associated with a cross dipole unit and then overlapping it with the other. Adjusting the phase at a medium frequency requires extra devices and a complicated system, what is more, the reliability of the device might be influenced by the environment. In this paper, the 4 I/Q components of a cross dipole unit are employed to compose the I/Q components of the signals associated with the circular polarization echoes. This method is very simple, and it only involves some basic calculations and judgments at each point. Theoretical analyses and numeral simulations show that this method is effective in removing the polarization characteristics.
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