An important issue in an information transmission system, for example, a data communication system over air, is to model and incorporate the effect of the input/output response of the transmitter, the medium (air), and the receiver in the analysis of the signals sent via this system. The simplest approach to this problem is to model the input/output response of the transmitter, the medium, and the receiver via a linear time-invariant system; the overall transfer function of these three is called the channel transfer function. More complicated models, which are based on linear time-varying systems, are currently being used to accurately model the channel effect.
A SAR transmitter/receiver is also an information processing system in which the user must be aware of the channel effect; that is, the effect of the radar transmitter, the propagation medium, and the radar receiver in the echoed signals stored in a computer for imaging. Yet a SAR channel is a multidimensional system that is a function of not only time (or radar frequency) but also space.
What we refer to as SAR radiation pattern is a measure that identifies the SAR channel effect. SAR radiation pattern is a measure of the relative phase as well as power (or magnitude) of the echoed signal due to a given target recorded in the computer; SAR radiation pattern is a complex (phase and magnitude) multidimensional signal. SAR radiation pattern of a target is a function of the following: