Reliability of active arrays

Reliability is the probability of a given performance being met over a certain length of time. Using this definition of reliability it is instructive to compare a hard and soft fail system. A hard fail system is one in which the system has only two performance states, working or failed. A passive array with a single power source is an example of such a system. The power source is a single point failure (SPF), if this fails the system fails. Incorporation of a second source, which can be used in the event of failure, increases the reliability of the SPF. But the system still remains a hard fail system, as it still only has two performance states. The author discusses the quantifying of graceful degradation of an active array. It is shown that, if a hard and soft fail system are designed to meet the same reliability, performance and lifetime, then a soft fail system, for a given reliability, will have a performance that is greater than the hard fail system, except at the equipment lifetime, where it is equal to it. The sidelobe level of a linear array was used to illustrate reliability as a function of performance