电磁波频谱如以下表格：Electromagnetic spectrumFrequ...

电磁波频谱如以下表格：Electromagnetic spectrumFrequency (Hz)PhotonenergyeV NameWavelength () Gamma ray ＜ 0.02 nm ＞ 15 EHz ＞ 62.1 keV X-ray 0.01 nm – 10 nm 30 EHz – 30 PHz 124 keV – 124 eV Ultraviolet 10 nm – 400 nm 30 PHz – 750 THz 124 eV – 3 eV Visible light 390 nm – 750 nm 770 THz – 400 THz 3.2 eV – 1.7 eV Infrared 750 nm – 1 mm 400 THz – 300 GHz 1.7 eV – 1.24 meV Microwave 1 mm – 1 m 300 GHz – 300 MHz 1.24 meV – 1.24 µeV Radio 1 mm – 100 km 300 GHz – 3 kHz 1.24 µeV – 12.4 feV Microwaves travel solely by line-of-sight paths; unlike lower frequency radio waves, they do not travel as ground waves which follow the contour of the Earth, or reflect off the ionosphere (skywaves). Although at the low end of the band they can pass through building walls enough for useful reception, usually rights of way cleared to the first Fresnel zone are required. Therefore, on the surface of the Earth, microwave communication links are limited by the visual horizon to about 30–40 miles (48–64 km). Microwaves are absorbed by moisture in the atmosphere, and the attenuation increases with frequency, becoming a significant factor (rain fade) at the high end of the band. Beginning at about 40 GHz, atmospheric gases also begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies (see graph at right). Above 100 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is in effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges. 下面描述错误的是：

A、微波工作频率介于射频及红外之间。

B、微波通信受大气吸收影响较大，衰减会随工作频率增加而加大。

C、微波导行系统一般功耗很大，无法长距离传输

D、微波通信有地波和天波 2 种模式