# 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 (EPAN) and the transverse face (EPAT). According to the TIA-222 standard, the total EPA of the ancillary can be determined using the following formula:
$$
(\mathrm{EPA})\_A = K\_a \left\[ (\mathrm{EPA})\_N \cdot \cos^2(\theta) + (\mathrm{EPA})\_T \cdot \sin^2(\theta) \right]
$$
where
* $$(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
### **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 cf 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 cf 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.
