Reflection and Scattering

Radar

Reflection / Absorption / Transmission

When electromagnetic waves hit an object,

part of the energy is reflected, part is absorbed, and the rest is transmitted through the material.

The ratio depends on frequency, material, and thickness.

1. RCS (Radar Cross Section)

Among electromagnetic wave interactions, reflection/scattering is the most important for radar, as it determines the returned signal strength.

RCS quantifies this reflection as an equivalent area, including both specular reflection and scattering effects, and varies with shape, material, and incident angle.

It is defined with respect to an ideal isotropic scatterer, serving as a reference for comparing reflected power under the same conditions.

PEC Sphere Example

A PEC sphere is commonly used as a practical approximation for RCS analysis.

In the high-frequency region, its RCS approaches the projected (cross-sectional) area, πR².

2. RCS Comparison by Materials

This table presents typical RCS values for various materials and objects in a home environment.

Higher RCS values indicate stronger reflected energy.

Additionally, even for the same material, RCS varies depending on the size of the object.

RCS Level	Material / Type	Examples	Typical RCS	Description
Reference	PEC Sphere (ideal conductor)	Ideal metal sphere	Depends on R σ ≈ πR²	Used as a conceptual reference; RCS approaches projected area (πR²) in high-frequency region
High	Metal (conductive objects)	Refrigerator, washing machine, metal cabinet	1 ~ 10 m² 0 ~ 10 dBsm	Strong reflection due to high conductivity
Medium	Human Body (complex scatterer)	Human	0.5 ~ 1.5 m² −3 ~ 2 dBsm	Irregular shape and internal structure produce complex scattering
Medium-Low	Water (high-loss dielectric)	Water tank, wet surfaces, large plants	0.2 ~ 1 m² −7 ~ 0 dBsm	Strong dielectric response with partial absorption
Low	Wood / Plastic (dielectric)	Table, chair, Furniture	0.01 ~ 0.1 m² −20 ~ −10 dBsm	Weak reflection
Very Low	Fabric/Soft materials	Curtain, clothes, bedding	0.001 ~ 0.01 m² −30 ~ −20 dBsm	Minimal reflection