📡How Ancillary EPA is Calculated

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:

where

• $(EPA)_N = (cf \cdot A)_N$

• $(EPA)_T = (cf \cdot A)_T$

• θ 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.

EPA=Area×cf,A=0.729×0.744 = 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

Area=Afrontal⋅cos(θ)+Aside⋅sin(θ)

cf,A=EPAArea

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

EPA=Area×cf,A=0.283×0.932 = 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

Area=Afrontal⋅cos(θ)+Aside⋅sin(θ)

cf,A=EPAArea

EN 1991-1-4:2005, ‍Eurocode 1: Actions on structures – Part 1-4: General actions – Wind actions.

TIA-222-I, Structural Standard for Antenna Supporting Structures, Antennas and Small Wind Turbines Support Structures, Telecommunications Industry Association, September 2023.