# Arrays and Infinite Periodic Structures

Infinite and finite periodic structures are efficiently modelled using special features available in Feko.

- Finite Antenna Arrays
- Finite antenna arrays where the elements are identical and the feed magnitude is
similar can be modelled using the domain Green's function method (DGFM). The method is
based on perturbation of the results from a single element and requires the elements to
identical and similar (not identical) in terms of currents flowing on the
elements.
Large finite arrays can also be approximated by infinite arrays by calculating the currents for the infinite structure, but then only taking a finite number of elements into account when calculating the far and near fields. The larger the array, the more accurate the approximations, since the error is the greatest at the edges of the array. These edge effects can also be taken into account (approximately) by modelling a finite array and using the currents of different elements (centre, edge, corner) to reconstruct the large array using radiating antenna sources.

- Infinite Arrays
- The periodic boundary conditions in Feko allow infinite 1D and 2D arrays to be modelled very efficiently. Users can either define the excitation or the phase difference between the elements.
- Frequency Selective Surfaces
- Frequency selective surfaces are also infinite structures and their properties can be investigated using the periodic boundary conditions method. Once their properties are known, approximations to these frequency selective surfaces are used to model complex, large, but finite, structures.