Fanbeam

Fanbeam refers to a type of radiation or signal beam that is wide in one plane and narrow in the orthogonal plane, producing a characteristic fan-shaped cross section. The term is used in several technical fields, including medical imaging, radiation detection, and antenna theory. A fan beam is typically generated by a line-shaped or curved source, or by collimation that limits emission to a narrow angular range in one direction while allowing a broader spread in the perpendicular direction.

In imaging and radiography, fan-beam geometry is common in computed tomography (CT) and fluoroscopy. In CT, a rotating X-ray tube and a curved detector array create a fan-shaped beam that irradiates a slice of the patient, enabling rapid data collection over a sector of angles. The reconstruction process must account for the geometry of the fan beam to produce accurate cross-sectional images. In gamma cameras, fan-beam collimation uses a similar principle to improve sensitivity for objects at certain distances or angles, at the cost of depth resolution.

In antenna and RF engineering, fan beams arise from linear arrays or cylindrical reflectors that produce directional radiation patterns that are wide in one dimension and narrow in the other. Such patterns are useful for surveying wide swaths of space or ground with relatively uniform coverage in one axis while maintaining angular resolution in the perpendicular axis.

Compared with pencil beams (narrow in both dimensions) or parallel beams (uniform spread in all directions), fan beams balance coverage and resolution by exploiting anisotropic geometry. Design considerations include collimation, detector or antenna aperture, and reconstruction or signal processing methods tailored to the fan-shaped geometry.