# RCS of double intake cavity using MDMM

RCS of double intake cavity using MDMM

This example is a double intake cavity where the cavity is 8 m deep. The entry of the cavity has a rectangular cross section with dimensions 1 m x 0.45 m. In the geometry of the problem is shown with the exterior geometry shown in grey transparent colour and the interior geometry, the cavity part, shown in green, blue, magenta and red colour.

We will compute the monostatic RCS for theta from 0 to 90 degrees at 500 MHz, for the polarisations HH (electric field parallel to X) and VV (electric field parallel to Y). In total we will compute the solution for 182 right hand sides.

We will demonstrate the flexibility, accuracy and efficiency of using the domain decomposition method used.

We will solve the problem in three different settings:

The problem is solved for the full problem in one single simulation using MLFMM solver. In this case the simulation is done on the whole geometry.

The problem is solved using the domain decomposition method with one interior cavity part (shown as section 1 to 4 in Figure) and one exterior part (shown in grey in Figure). Two simulations are done, one for the interior problem, and one for the exterior problem. At the interface surface between the interior and exterior domains the electric field is expanded using 9 TE and 3 TM modes. After the two simulations have been done continuity of the fields are enforced at the interface surface between the interior and exterior. This determines the correct surface currents and the far field and RCS can be computed. The interior simulation is done using MoM and the exterior simulation using MLFMM.

The problem is solved using the domain decomposition method with four interior cavity parts (one simulation for each section in Figure) and one exterior part (shown in grey in Figure ). At the interface surface between the interior and exterior domains and at the interface surfaces between section 2 and section 3 and section 2 and section 4 the electric field is expanded using 9 TE and 3 TM modes. At the interface surfaces between section 1 and section 2 the electric field is expanded using 17 TE and 6 TM modes. After all simulations have been computed the interior results (admittance- and scattering-matrices) are merged to one result for the interior part. When this is done continuity of the fields are enforced at the interface surface between the interior and exterior. This determines the correct surface currents and the far field and RCS can be computed. The interior simulations are done using MoM and the exterior simulation using MLFMM.

Fig 1 Geometrical structure of double intake cavity

Fig 2 Total monostatic RCS at 500MHz for VV polarization

Fig 3 Monostatic cavity RCS at 500MHz for VV and HH polarization.

Fig4 Monostatic perfectly matched RCS at 500MHz for VV and HH polarization.

Fig5 Number of iterations for computation on full model and computation on exterior part of decomposed model

Fig 6 Surface currents