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Physical Optics (PO)

Physical Optics (PO)
mom_po_theoretical_small
Accurate MoM applied to source
and triangular based PO applied
to scattering region.

General Applicability of the Technique

PO is formulated for use in instances where electrically very large metallic or dielectric structures are modelled.  PO is an asymptotic high frequency numerical method of the same nature as the UTD, but is based on currents and not rays.  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 and if they still can not solve the problem in the available resources, then PO.

 

Technical Foundation (Hybrid MoM/PO)

FEKO hybridises the current-based accurate MoM with PO in the truest sense of the word with bidirectional coupling between the MoM and PO being maintained in the solution, in other words modification of the interaction matrix, ensuring accuracy.  A practical example would be to calculate the effect on the input impedance of a horn antenna, treated with the MoM, when in close proximity to a large structure treated with the PO.  FEKO triangulates a PO region, exactly the same as it would for a MoM solution, making it a simple task to switch between solution options.

FEKO implements a number of extensions to the PO:

  • Fock currents to account for the effect of creeping waves over the shadow boundary region into "unlit" areas.

  • Correction terms to achieve more accurate current representation close to edges and wedges.

  • Large element PO (LE-PO): this is an alternative set of basis functions for the PO, based on plane wave functions. LE-PO does not support multiple reflections, but allows mesh sizes of multiple wavelengths. This leads to dramatic computational cost savings relative to standard PO, in cases where LE-PO is applicable.

  • Multilevel Fast Multipole Method (MLFMM) hybridisation:  the MoM region of a hybrid MoM/PO or MoM/LE-PO problem may be solved with the MLFMM.  This enables the efficient solution of large MoM domains along with PO and LE-PO domains for optimal inclusion of complex full wave domains in the hybrid problem.

 

Typical Application of the PO

A typical example of how the MoM/PO hybridisation can be employed with good effect is in the analysis of reflector antennas. A large reflector antenna may be too large to analyse with the MLFMM, in which case a combination of MoM and PO is the ideal solution. The feed structure will typically be modelled with the MoM to achieve high accuracy in the currents on this part of the structure, with the reflector itself being modelled with the PO. In such a case, both the standard and large element PO will be suitable. Note that modal waveguide ports may be used in the MoM region of a hybrid MoM/PO analysis, enabling FEKO to deal very efficiently with horn feeds.

PO_dish_MoM_feed
PO modelling of a reflector antenna with MoM modelling
of the feed.
Additional Information

Additional Information