 are addressed. Since this subject alone could generate an entire chapter unto itself, the present scope will be limited to an assessment of the various general functional circuit topologies that may be employed. In addition, some insight will be given to implementation degradations which can further act to diminish the real effectiveness of the more complex detection approaches. 1.2.3.1 Basic Configurations (1) Wideband Single-Channel Detectors Many wideband radiometers have been built to operate in the SHF and EHF frequency bands, and have been used extensively for ground, airborne, and spacecraft applications. As a result, the technology needed for this type of detector is fairly well at hand. From a functional standpoint, a most difficult problem is that of setting and maintaining the receiver threshold value. Proper setting of the comparator threshold voltage relative to the output of the integrator is essential to meeting the specified PD and PFA- If the thresh- old is too low, an excessive false alarm rate is obtained while, if it is too high, detection of an actual signal may be missed. Even if the threshold is set prop- erly initially, time, temperature, and voltage variations, and other dynamic conditions, will affect the overall receiver gain such that the initial setting will become incorrect. Further, the receiver effective noise temperature will also change with interceptor altitude and attitude (as the receiving antenna is subjected to varying background temperature due to changing angles and field of view). Thus, some precise, automatic, periodically updating method of threshold determination is needed. Since the signal to be detected and the noise are uncorrelated but have a definite power ratio for a given PD and PFA at a specified SIN and Wss, it is necessary onoly to measure the noise level in the absence of signal in order to derive the independent variable which permits threshold calculation or establishment. Although elementary in principle, the implementation of this concept gives rise to 