![]() ![]() In our case we assume that the antenna is facing normal to the wind, so $\theta = 0^\circ$. $$(EPA)_A = K_a$$ where $\theta$ is the relative angle between the azimuth associated with the normal face of the appurtenance and the wind direction. TIA code suggest the following formula for computing the total EPA of the appurtenances. EPA areaįrom here it is a simple step to calculate the EPA area of the antenna. For the curious, in case we wouldn't have any smooth edge on the antenna, then our $C_a$ value would yield to $1.43$, thus would be a significant increase on the drag area. Meaning that our EPA area is smaller eventually than the FPA. ![]() It still not close to a Carrera 911 but we should appreciate this value as its already smaller than 1.0. If the drag force on an antenna is known, the antenna's drag coefficient can be calculated using the following equation: Its value varies for each antenna shape and must be determined experimentally or with the aid of Computational Fluid Dynamic (CFD) analysis. The drag coefficient is a key component in calculating wind load on an antenna. In fact, the new Porsche Carrera 911 (992 model) has a drag coefficient of 0.29.īut back to our antennas, how the drag factor actually impacts the wind load on the antennas? We can look at different design codes, but the basic principal to compute force coefficient for a particular antenna (or other objects too) is the following. While we are having values in the range of 0.7 - 1.6 for antennas, in the car industry it is not very difficult to find drag factors of cars under 0.3. ![]() We'll discuss the wind loads in a second. So from here we can see that how the antenna shape is a significant factor to establishing wind loads on them. The then by calculating the EPA of the antennas multiplying the $FPA $ with their respective $C_f$ values, the results will be proportionally the same. In the last case there is a "wind-friendly" panel antenna with nice and smooth edges. In the middle, antenna has a round shape exposed to wind which gives a significantly lower $C_f$ value, about $0.8$. In the first case the antenna has a flat area exposed to the wind with fairly sharp edges. However, their force coefficient, $C_f$ (or drag factor) are very different due to their shapes. EPA of antennas with different shapes and edges.Īll three antennas have the same flat plate area (FPA) as $1.0m^2$. ![]()
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