Antenna radio wave attenuation during rain

Antenna radio wave attenuation during rain

Figure 1 shows a schematic diagram of how radio waves are attenuated by rain, using a BS antenna as an example.
The attenuation of radio waves during rain is not only due to the rain between the satellite and the BS antenna, that is, the attenuation caused by raindrops in space.
water film attenuation.
Water film attenuation is the attenuation of radio waves due to the water film that forms when rain adheres to the BS antenna.
This water film attenuation can be prevented.
When Super hydrophobic material HIREC is applied to the surface of a BS antenna, almost no water film is formed on the surface, making it possible to significantly reduce water film attenuation.There is something called

Figure 2 shows the relationship between rainfall intensity and rainfall attenuation.
Attenuation due to rainfall occurs at frequencies above 10 GHz, and the higher the frequency, the greater the amount of attenuation. Attenuation increases with increasing rainfall.
For example, in the 12 GHz frequency band, which is the frequency band of BS, the rainfall intensity is 5mm/h and 10mm/h, and the rainfall attenuation is about 1dB and about 2dB, respectively.

The figure above shows the relationship between frequency and water film attenuation with the thickness of the water film as a parameter. (Calculated based on the formula for water film attenuation in Meteorological Research Note No. 112 and complex permittivity data of water)
It can be seen that water film attenuation occurs even at frequencies of several GHz, and the higher the frequency and the thicker the water film, the greater the attenuation.
The thickness of the water film at a certain rainfall intensity varies depending on the size and shape of the antenna.
In a radome shape with a diameter of 5m at 10℃, the rainfall intensity is 10mm/hr and the water film thickness is about 0.16mm. From this example, it seems that a 0.1-0.2mm thick water film can be formed even by normal rainfall.
In addition, considering deterioration of the antenna surface due to ultraviolet rays, even with the same antenna, the longer the outdoor installation period, the thicker the water film, even with the same amount of rainfall.

Figure 4 summarizes the rainfall attenuation data in Figure 2 and the water film attenuation calculation results in Figure 3.
This shows that the influence of water film attenuation is not small. Water film countermeasures are especially important at frequencies around 10 GHz and below.
If the antenna surface is treated with Super hydrophobic to strongly repel water, radio wave attenuation due to water film will hardly occur below 10 GHz.
Rain attenuation occurs above 10 GHz, but since the water film attenuation can be eliminated, the overall attenuation can be expected to be reduced.

Examples of measures against rain on antennas

 

Figure 5 is an example of actual measurement of radio wave reception characteristics with a BS antenna (12GHz band).
When comparing the presence and absence of the Super hydrophobic material HIREC, during rain (17:00 to 19:00) antennas without HIREC experienced approximately 3-4 dB attenuation, whereas antennas coated with HIREC experienced attenuation of approximately 3-4 dB. There is no attenuation in the antenna.
The rainfall intensity is unknown, but since there is no attenuation in the antenna coated with HIREC, it is estimated to be less than 5mm/h based on the graph of rainfall intensity and rainfall attenuation.
In addition, in the graph of rainfall intensity and rainfall attenuation, the rain attenuation in the 12 GHz band at a rainfall intensity of 5 mm/h is approximately 1 dB, so the 3-4 dB attenuation in Figure 3 is not due to rain attenuation but to water film. It can be interpreted as attenuation.
Furthermore, the fact that attenuation occurs even after 7pm after the rain has stopped confirms that the attenuation is caused by a water film still existing on the antenna surface.
In other words, if it rains on the antenna, water film attenuation will occur for a while even after the rain has stopped. On the other hand, the antenna coated with Super hydrophobic material HIREC did not experience any attenuation, indicating that almost no water film was formed on the antenna surface.
Based on the above, Super hydrophobic material HIREC can be said to be one of the effective measures against water film attenuation.
Finally, there is talk that water film attenuation occurs even at frequencies below 10 GHz, but this is currently unconfirmed, so we will add the latest information as soon as we know the situation.

Examples of snow countermeasures using Super hydrophobic sheets on antennas

Super hydrophobic sheets can be worn even in winter.

Traditionally, snow countermeasures have mostly been applied directly to antennas, etc., but the problem was that in winter, temperatures dropped and construction could not be carried out on site.
Therefore, we will introduce an example of a Super hydrophobic sheet that can protect field equipment from snow even in winter.

Advantages of Super hydrophobic sheets

• Can be installed even in winter ← On-site painting of the antenna at temperatures below 5°C is not possible.
• Can be installed in 1-2 hours ← At least 2 days required for on-site installation of the antenna

Disadvantages of Super hydrophobic sheets

• Approximately 1 year life (depending on the weather resistance of the sheet material) ← Approximately 3 years for conventional on-site painting

*Material of Super hydrophobic sheet: Polyethylene (PE) or polyester
*Super hydrophobic covers are custom made. Please contact us.

Structure and reality of Super hydrophobic sheet

Reflector: Super hydrophobic sheet
Polyethylene or polyester sheet (blue part) is coated with Super hydrophobic material [HIREC undercoat (light green part)] HIREC 100 (red part)] is applied. 

• The photo on the right shows Super hydrophobic sheet attached to the reflector of the antenna.

Converter (radio wave condensing part): Only HIREC 100 (red part) is painted with a brush

• HIREC 100 is a functional material and not a paint, so brush marks (irregularities) will occur when applied with a brush. White irregularities are evidence of good Super hydrophobic. (Enlarged view of converter)

Comparison of radio reception status with and without Super hydrophobic during snowfall

Radio wave reception status of BS antenna during snowfall (Situation about 14 months after installation of BS antenna)

With the untreated Super hydrophobic repellent antenna, there were several reception interruptions (tuner reception level below 20),
An antenna equipped with a Super hydrophobic repellent cover (the converter is also Super hydrophobic)was able to receive signals normally, although the level decreased.

Radio wave reception status of the BS antenna during snowfall (approximately 26 months after antenna installation)

Super hydrophobic repellent raw BS antenna
With untreated Super hydrophobic repellent BS antennas, during the 54-day recording period, reception was not possible (reception level was below 20) or video disturbances were observed for several 10 minutes to nearly 9 hours per day.
The frequency is 15 times.

Super hydrophobic repellent BS antenna
With Super hydrophobic repellent BS antenna,there was no frequency where the reception level was below 25.

Detailed example of radio wave reception

I was able to successfully receive BS broadcasts because Super hydrophobic repellent This is because almost no water film was formed on the antenna and converter parts.It can be estimated.
There are snow melting devices available to prevent snow from accumulating on antennas. The main cause of radio wave attenuation is not snow or ice, but water (water film). Therefore, antenna snow melting equipment may not be effective in reducing radio wave attenuation.

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