why the RE antenna height in only up to 4m?

amo

最近群里又在讨论标准，说到天线高度的问题，再加上论坛上一个兄弟也在讨论这事。

于是我去问了IEC的专家。下面是他们的回复，更为专业一些 

Dear Mr. Changbing,

    due to the superposition of direct radiation from the EUT and radiation from the EUT reflected on the ground plane to the measurement antenna, the antenna height for maximum field strength varies with measurement distance, frequency, EUT height and polarization. The maximum antenna height cannot be predicted due to the unknown EUT phase center of radiation. This is the reason why the antenna height has be varied from 1 m to 4 m. For a measurement distance of 3 m, the antenna height of maximum field strength is usually between 1 m and 2,5 m. For a measurement distance of 10 m, the antenna height of maximum field strength is between about 1 m and 4 m. Around 30 MHz the antenna height for horizontal polarization of 4 m for 10 m measurement distance is a compromise. The actual maximum is above 4 m.

Attached are two figures showing the height of maximum field strength designated with 'x' for an EUT phase center of 1 m height, horizontal (left) and vertical (right) polarization at 3 m measurement distance. The vertical lines show the antenna height where the field strength is within 3 dB of the maximum field strength. Unfortunately I have this paper published in 1990 only in German, but I hope the explanation helps.

You can also find indications on the antenna-height setting in CISPR 16-2-3 ed. 3 Clause 8.

----------------------explanation by Manfred Stecher ,Chairman of CISPR Subcommittee A

pwm

牛——就是一个单词：OX。

mic29

amo真牛！