Engineering topics

Chou, Ri-Chee

Publications and source records attributed to Chou, Ri-Chee.

4 records

NASA NTRS1989

High-frequency RCS of open cavities with rectangular and circular cross sections

The radar cross-section (RCS) analysis of open-ended cavities with rectangular and circular cross sections is carried out using the waveguide modal approach and the shooting-and-bouncing ray (SBR) approach. For a cavity opening on the order of ten wavelengths or larger, the comparison between the two approaches is excellent. It is also observed that at lower frequencies the SBR results deviate from the more accurate modal results. On the other hand, the SBR approach allows for greater flexibility in geometrical modeling, and can be applied to problems where waveguide modes cannot be easily found. SBR results for an offset rectangular cavity and a circular cavity with rounded endplate are presented.

Ling, Hao↗

NASA NTRS1989

Shooting and bouncing rays - Calculating the RCS of an arbitrarily shaped cavity

A ray-shooting approach is presented for calculating the interior radar cross section (RCS) from a partially open cavity. In the problem considered, a dense grid of rays is launched into the cavity through the opening. The rays bounce from the cavity walls based on the laws of geometrical optics and eventually exit the cavity via the aperture. The ray-bouncing method is based on tracking a large number of rays launched into the cavity through the opening and determining the geometrical optics field associated with each ray by taking into consideration (1) the geometrical divergence factor, (2) polarization, and (3) material loading of the cavity walls. A physical optics scheme is then applied to compute the backscattered field from the exit rays. This method is so simple in concept that there is virtually no restriction on the shape or material loading of the cavity. Numerical results obtained by this method are compared with those for the modal analysis for a circular cylinder terminated by a PEC plate. RCS results for an S-bend circular cylinder generated on the Cray X-MP supercomputer show significant RCS reduction. Some of the limitations and possible extensions of this technique are discussed.

Ling, Hao↗

NASA NTRS1988

Modal attenuation in multilayered coated waveguides

Propagation and attenuation constants of low-order normal modes in a circular waveguide lined with lossy coating layers are calculated using a generalized dispersion equation. It is found that the use of multilayered coating can significantly enhance modal attenuations over a broader frequency range compared to that for a single-layer coated structure. For a cylinder with radius a = 2 lambda, the attenuation constants for the dominant modes are shown to increase by 20 dB per a by adding a lossless padding layer to a lossy magnetic coating. Application of this result in radar cross-section (RCS) reduction is discussed.

Chou, Ri-Chee↗

NASA NTRS1987

Rays versus modes - Pictorial display of energy flow in an open-ended waveguide

The problem of a plane wave impinging on a semiinfinite parallel-plate waveguide is investigated. It is demonstrated that, for waveguide separation large compared to the wavelength, the fields inside the waveguide obey a single ray optics description. The beam behavior persists for more than 1000 lambda into a 50 lambda waveguide. For a small 3 lambda waveguide, the beam picture begins to blur approximately 5 lambda into the guide.

Ling, Hao↗