Calculating Ancillary EPA in Shapemaker Using Eurocode and TIA-222

Ancillary EPA calculation method in Shapemaker

The Eurocode does not specify a precise method for calculating effective projected areas on ancillaries. However, a well-established approach is provided by the TIA-222 standard. This method involves calculating the EPA of the antenna faces — specifically, the normal face (EPA_N) and the transverse face (EPA_T). According to the TIA-222 standard, the total EPA of the ancillary can be determined using the following formula:

$$(EPA)_A = K_a[(EPA)_N \cdot cos^2(\theta)+(EPA)_T \cdot sin^2(\theta)]$$

where 

• (EPA)_N = (c_f x A)_N
• (EPA)_T = (c_f x A)_T
• $\theta$ is the relative angle between the azimuth associated with the normal face of the ancillary and the wind direction
• Ka is the shielding factor associated to the ancillary for which we calculate the EPA - see here how Shapemaker calculates shielding factors automatically

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Force coefficients in Shapemaker (c_f)

Several ancillary shapes have been identified for which the force coefficients and the EPA are calculated.

• box
• cylinder
• dish
• plane lattice

All ancillary types in the Shapemaker database are associated with a specific shape.

• GSM/RRU/MHA/FTTA are box shapes
• OMNI/GPS are cylinder shapes
• All MW dishes are dish shapes
• Dipole/Yagi are plane shapes

In Shapemaker there are 3 input methods for the force coefficient:

1. (default) calculated according to standards:
   
   1. EN 1991-1-4 2005, Chapter 7.6, Chapter 7.9 and Chapter 7.11 for box, cylinder and plane lattice shapes respectively
   2. TIA-222-I, Annex C for dishes
2. user input - specify directly the force coefficients for Front, Side and Rear of the ancillary
3. calculated based on forces from the manufacturer's technical sheets.

Example 1

EPA calculation of a box shape using EN 1991-1-4 and TIA-222-I

Ancillary specification: GSM Antenna: H2000 / W400 / D190 / R20 (mm).

Antenna azimuth: 0°.

Wind direction: 60°.

Dimensions below in meters.

In the Shapemaker report, the EPA is presented separately as Area and c_f,A. When you multiply them, you get the EPA for 60° wind direction.

$\text{EPA} = \text{Area} \times c_{f,A} = 0.729 \times 0.744$ = 0.54 m²

To be able to show the values in the report in one line and make the ancillaries table more compact, Area and c_f are calculated as below.

EPA = 0.54 m²

$\text{Area} = A_{\text{frontal}} \cdot \cos(\theta) + A_{\text{side}} \cdot \sin(\theta)$

$c_{f,A} = \frac{\text{EPA}}{\text{Area}}$

Example 2

EPA calculation of a dish shape using TIA-222-I

Ancillary specification: MW Dish with shroud: Dia600 / Depth200 (mm).

MW Dish azimuth: 0°.

Wind direction: 50°.

Dimensions below in meters.

EPA in the Shapemaker report

$\text{EPA} = \text{Area} \times c_{f,A} = 0.283  \times 0.932$ = 0.263 m²

To be able to show the values in the report in one line and make the ancillaries table more compact, Area and c_f are calculated as below.

EPA = 0.263 m²

$\text{Area} = A_{\text{frontal}} \cdot \cos(\theta) + A_{\text{side}} \cdot \sin(\theta)$

$c_{f,A} = \frac{\text{EPA}}{\text{Area}}$