The engine of a fighter plane is one of the largest scattering centers of the entire aircraft. One possible way of reducing the radar cross section (RCS) of the engine is to use an S-shaped bending air inlet to avoid direct radar wave illumination and reflection. We evaluate the efficacy of an S-shaped air inlet on RCS reduction by simulating the boresight and ±15˚ bistatic RCS for a digital model of an engine located behind an S-shaped inlet, using a multi-level fast multipole method (MLFMM) code in the S and X bands. The results show that a curved S-type air inlet can reduce the engine boresight bistatic RCS by ~10-12 dBsm at 3 GHz, and ~16 dBsm at 10 GHz when radar wave is incident from boresight, but not to the level required by RF stealth standards. When the radar waves are incident from θ=105˚ φ=90˚ or θ=90˚ φ=345˚, the RCS reduction is less effective, which is the results of the bend direction of the S-type air inlet.
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