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