# Uniform Theory of Diffraction (UTD)

Uniform Theory of Diffraction (UTD)
 Accurate MoM applied to source and UTD applied to large polygonal plate.

### General Applicability of the Technique

The UTD is formulated for use in instances where electrically extremely large structures are modelled. The UTD is an asymptotic high frequency numerical method of the same nature as the PO. Users will typically attempt a solution with the MoM at first and when they realise that the structure is electrically too large to solve with their available resources (platform memory, time) they will turn to the MLFMM, PO and lastly UTD.

### Technical Foundation (Hybrid MoM/UTD)

FEKO hybridises the current based accurate MoM with the UTD in the truest sense of the word with the bidirectional coupling between the MoM and UTD being maintained in the solution, i.e. modification of the interaction matrix, ensuring accuracy. A practical example would be a changing input impedance of a dipole treated with the MoM, in close proximity to a large structure treated with the UTD. Frequency does not influence the memory resources required for UTD treatment of a structure as only points of reflection from surfaces and diffraction from edges or corners are considered without meshing the structure. Multiple reflections, edge and corner diffraction, double diffraction and creeping waves (cylinders) are taken into account. Insight into the propagation of rays are provided in POSTFEKO during postprocessing. Currently the numerical formulation of the UTD only allows it to be applied to flat polygonal plates with minimum edge length in the order of a wavelength or to single cylinders. The UTD is thus quite well suited to the analysis of ships at radar or EW frequencies, but not well suited to the analysis of complex objects with curved surfaces, e.g. automobiles.

### Typical Application of the UTD

A typical application of the UTD is to analyse coupling between high frequency transmitters on the superstructure of a ship. UTD rays can help determine which transmission paths provide significant coupling to enable designers to relocate the offending transmitter to a location where it will interfere less, or to dampen the main path of interference with RF absorbing material.

 UTD modelling of cross-coupling on the superstructure of a modern naval vessel. Analysis of the transmission patterns of an X-band radar mounted on a ship.