directivity

1.and so for an ideal antenna gain & directivity correspond exactly.

é = Prad /边 ， 此理想的天线增益方向完全一致。

2.Laser is a new light source.Comparing with ordinary light the laser has good monochromaticity, directivity, coherency, high brightness, high power and high energy etc.

摘要激光是一种新型光源，激光与普通光相比，具有很好的单色、方向、相干亮度以及功率、能量等特点。