To protect the air defense surveillance radar station nearby the electromagnetic interference of UHV transmission lines

according to radar position requirements

we analyzed the distance between UHV transmission lines and air defense surveillance radar station

proposed an estimation model for shielding loss of UHV lines to radar waves. The radio noise of the Ximeng-Shandong UHV project was measured. The transmit antenna was assigned at 1 660 m away from the lines. On the other side of the line

signals were received by antenna and spectrum analyzer carrying by unmanned aerial vehicle from 20～350 m high altitude.Shielding loss of electromagnetic waves by lines was measured at 80～3 200 MHz. The results indicate that the radio noise of AC UHV transmission lines are close to the background at 80～1 000 MHz. There is no obvious consistency difference before and after the transmission lines live state without interfering with radar reception. The shielding loss of UHV lines to electromagnetic waves is between –5.2～2 dB. The shielding loss in the region under the lowest conductor is –5.2～2 dB. The shielding loss is –2.2～1.8 dB when the shielding area is formed by the lines

approximate to empirical formula estimation.The loss in the region above the highest conductor is rapidly reduced to background fluctuation. The shielding loss decreases with the increase of frequency. The protection distance between UHV transmission lines and radar should be classified by radar type. For meter wave radar

the protection distance is decided by the position requirements and the shielding angle. For L and S band radar

the protection distance is determined by the elevation angle. The electromagnetic effect of UHV lines on radar can be reduced by lowering the lines height or increasing the radar antenna

or by utilizing the favorable terrain with elevation difference.