IEEE 145-1993 Historical

It is assumed in this standard that an antenna is a passive linear reciprocal device. Thus, where a definition implies the use of an antenna in a transmitting situation, its use in a receiving situation is also implicit, unless specifically stated otherrewise. When an antenna or group of antennas is combined with circuit elements that are active, nonlinear, or nonreciprocal, the combination is regarded as a system that includes an antenna. Examples of such cases are an adaptive antenna system and a signal-processing antenna system; the complete conical-scanning, monopulse, and compound interferometer systems also fall in this category. For terms that are quantitative, it is understood that frequency must be specified. For those in which phase or polarization is a significant part of the definition, a coherent source of power is implied. Whenever a term is commonly used in other fields but has specialized significance in the field of antennas, this is noted in the title. When applying terms pertaining to radiation characteristics, such as gain, polarization, beamwidth, etc., to multiple-beam antennas, each port shall be considered to be that of a separate antenna with a single main beam. For polarization diversity systems that may include active devices, these terms apply to each polarization state for which the antenna is adjusted. Throughout this standard, where phasors are used, or are implied, the time convention shall be taken to be exp(jwt).