Atmospheric absorption and scattering losses offer a means of protection against cochannel interference in RF communications links that operate above 18 GHz. By varying the operating frequency of such a link, the communicator can adjust the atmospheric attenuation of the signal and interference in order to improve link performance. If the effective length of the interference path exceeds that of the signal path, significant enhancement of the link's signal-to-interference-plus-noise ratio (SINR) can result. In many situations an optimal frequency exists at which the link SINR reaches a maximum value that substantially exceeds the values obtainable elsewhere in the available frequency band. This paper develops a technique for identifying the optimal operating frequency, and predicting the resultant SINR enhancement, on the basis of given equipment and environmental characteristics. The technique is applicable to the conceptual design of communications systems in the EHF and high SHF bands.

A simple formula is derived for identifying intermodulation (IM) mixes that are capable of generating IM products that fall within the same frequency band as the intermodulating signals. The formula is valid for any frequency band, any IM order, and any number of signals. Examples of its use are given.