Absorber
Understanding RF Absorbers
RF absorbers are essential for accurate antenna measurement, EMC testing, and radar signature reduction. Without absorbers, reflections from walls, floors, and equipment would contaminate measurements and create standing waves.
Absorber Types
- Pyramidal foam: Carbon-loaded polyurethane foam in pyramid shapes. Best performance at normal incidence. Standard for anechoic chambers. -30 to -50 dB reflectivity.
- Flat sheet: Magnetically or dielectrically loaded rubber or foam. Thinner than pyramidal. Used for cavity lining and surface applications.
- Ferrite tile: Sintered ferrite tiles. Very thin (5-6mm). Effective 30 MHz - 1 GHz. Used in compact anechoic chambers.
- Hybrid: Ferrite tiles with pyramidal foam overlay. Broadband from 30 MHz to 40+ GHz.
Frequently Asked Questions
What is an RF absorber?
An RF absorber converts electromagnetic energy to heat instead of reflecting it. Used in anechoic chambers, on military platforms (stealth), and in circuits to prevent resonances. Performance is specified by reflectivity, typically -20 to -50 dB.
What is an anechoic chamber?
An anechoic chamber is a shielded room lined with RF absorbers that simulates free-space conditions by eliminating reflections from walls, ceiling, and floor. Used for antenna pattern measurement, EMC testing, and radar cross section measurement.
What is the difference between pyramidal and ferrite absorber?
Pyramidal foam absorbers are thick (up to 2m for low-frequency performance) but provide the best reflectivity above 200 MHz. Ferrite tiles are thin (~6mm) and effective 30 MHz - 1 GHz. Combining both provides broadband coverage.