Why it is so hard to find small radio frequency signals in the presence of large signals

The essence of radar, radio and wireless sensor engineering is extracting small information-bearing signals. This is notoriously difficult and engineers compensate by transmitting high power signals, reducing range, and spacing wireless systems in frequency and time. New understandings of passive intermodulation distortion, thermal effects, time-frequency effects, and noise are presented. It is seen that the familiar frequency-domain-based abstractions have missed important underlying physics. Through greater understanding, RF engineers can develop microwave systems with far lower levels of distortion and noise.