A broadband microwave signal to noise enhancer

A signal to noise enhancer exhibits a high attenuation to small noise level signals and a lower attenuation to larger above threshold signals. The devices described rely on magnetostatic waves as saturable absorbers of power from a microwave transmission line, typically microstrip. Experiments performed with epitaxial YIG show that instantaneous bandwidths of 900 MHz with threshold levels of less than 0 dBm can be obtained below 4.2 GHz. Enhancement of greater than 20 dB can be achieved for an increase in power level of 20 dB above threshold. Characteristics obtained with lithium ferrite in the 4-8 GHz band are comparable to those obtained with YIG in the 2-4 GHz range. Owing to the increased fmr and spin wave linewidth of the lithium ferrite, the threshold level is higher, + 6 dBm, and the frequency selectivity poorer than observed with YIG.