中文摘要：

提出在短波通信中利用发射端窄波束，在空间上将能量集中于主路径且抑制其他路径来改善多径信道环境；并基于一种时变双层平谷电子密度模式对窄波束信道特性进行了理论分析。以中纬度地区的中距离通信为例，计算了不同时刻使用不同发射天线数时的信道参数，并计算了特定窄波束的服务区间范围。理论分析和计算结果均表明：在短波通信中使用发射窄波束，主路径相对其他路径的功率比值增益以及信道相干带宽都会显著提高。

英文摘要：

The authors propose a method of using transmit narrow-beam to spatially concentrate the radiation energy on dominant path and suppress undesired paths in the shortwave communication. Based on the time-variant double layers ＆ plane valley electron density profile, the theoretical analysis of narrow-beam channel characteristics is conducted. Under the mid-latitude mid-range communication, the calculations of channel parameters are taken for different number of transmit antennas at different time and the serving region size is calculated for certain narrow beam. Both the theoretical study and the calculation results show that the gain of the power ratio of dominant path to the others and the coherence bandwidth can be dramatically increased in the shortwave communication with narrow-beam.