TABLE OF CONTENTS Noise analysis of microwave circuits and systems has been a research issue for many decades. A circuit's noise performance is given in terms of noise figure or noise temperature. The signal energy exiting a generator or antenna is amplified or attenuated in passing from the input to the output of a two-port network. Along this signal path, thermal energy in the components add noise to the signal. In some applications, e.g., in a radar receiver, it is necessary to anticipate the amount of noise that circuits add to the signal path. When receiving a radar pulse, the receiver will also add some noise to the signal. This added noise masks the pulses, which will it make more difficult to detect them. When the ratio of pulse power to noise becomes too low, the pulse and the target cannot be detected. Thus, a receiver that adds the least amount of noise possible is desirable. There is a similar requirement for a microwave radio. A microwave signal is modulated with data and transmitted from an antenna on top of a mountain. A receiver on a neighboring mountain ridge receives this signal and extracts the data. When the signal becomes overwhelmed by noise, however, the data stream can no longer be reconstructed.
Section 8.2 introduces a model for the generation of random noise. We will study thermal noise, which has constant power at any frequency of interest to us. Thermal noise can be modeled as voltage and current sources that...
