Damping spurious microwave response with absorbing materials

It is pointed out that iron-loaded resins absorb microwave energy and can be added to microwave devices to ensure their intended performance. The iron particles are chemically formed, perfect spheres of microscopic dimension with a diameter of about 10 microns. The loss mechanism is a combination of magnetic hysteresis in the iron and resistance loss in the surface of the iron spheres. The loss is negligible in the VHF-UHF range. For this reason, these materials find most practical uses above about 1 GHz at frequencies at which the TEM loss becomes sufficient to perform useful functions within practical dimensions. Attention is given to applications of microwave absorbers, the preservation of high frequency rejection in low frequency filters, the use of microwave absorbing material to absorb energy leaking into the strictly mechanical portion of a tunable resonant cavity, transmitter harmonic suppression, and the preservation of constant gain in broadband amplifiers.