Radar Cross Section Modeling and Measurements of Inlets and Cylinders With Skew Blades

Abstract

Ray based methods give useful scattered field predictions from the skin of the aircraft illuminated by an incident plane wave. They can also be used to predict the returns from simple inlets and cavities but fail when complex terminations such as skewed blades are encountered. As a possible enhancement to the ray-tracing procedure, an auxiliary program based on the modal method was developed to predict the scattering of electrically large and complex jet inlets with engines. For the present development, it is assumed here that these structures can be approximated by a series of rectangular, circular, coaxial and sectoral waveguide sections. The field matching technique is used to give the generalized scattering matrices of the junctions between these waveguide sections. By combining the scattering matrices of the waveguide sections representing the inlet and engine, an overall S-matrix is obtained. Knowing the modes induced at the inlet aperture by the incident plane wave, the scattered fields from the inlet and engine can be readily predicted in all directions. Monostatic RCS measurements of a 0.706 m diameter test cylinder containing 30 skewed blades mounted on a center shaft with a conical hub have been performed at X-band. The dimensions of the structure, the number and orientation of the blades are consistent with those of existing jet engines. Fair to good agreement between predictions and measurements verify the developed software and analytical method used.Index Terms-Cylinder with skew blades, jet engine inlet, mode matching method, radar cross-section prediction and measurement.

Comparative study of miscellaneous methods applied to a benchmark, inlet scattering problem

“…However, it has provided the earliest numerical results for this cavity configuration, and is therefore used as computational reference. More recently developed software based on MM is described in [10].…”

“…The simplified inlet model was first adopted in [2], and further analysed in [3–11]. There are two basic versions of this model, one with straight blades, depicted in Fig.…”

“…Naturally, early stages of the TG involved the characterisation of simplified, engine-like structures, which could serve as a validation benchmark for the computer codes owned and/or developed by the partners. It was agreed that a good candidate for such a benchmark geometry was the configuration originally proposed in [2], whose various versions were subsequently addressed in a series of related papers [3][4][5][6][7][8][9][10][11]. Although RCS measurements were originally carried out in [12], it was decided that an additional measurement campaign was necessary on a newly built model, to achieve further flexibility of the TG activities.…”

“…2 Simplified jet engine inlet model design, fabrication and measurements The simplified inlet model was first adopted in [2], and further analysed in [3][4][5][6][7][8][9][10][11]. There are two basic versions of this model, one with straight blades, depicted in Fig.…”

RCS Reduction of Open-Ended Circular Waveguide Cavity With Corrugations Using Mode Matching and Scattering Matrix Analysis

“…The first is an exact solution using a mode matching method with a scattering matrix analysis [2][3][4][5][6]. In this method, the jet engine is treated as a complex open-ended waveguide cavity structure.…”