Electromagnetic radiation is often caused by time-varying currents that are not meant to radiate. The distances currents travel, the geometries of the paths they follow, and the frequencies and amplitudes of their sinusoidal components all contribute to that radiation. Nevertheless, those aspects of current behavior seldom receive sufficient attention during the design and implementation of most electrical and electronic devices. In fact, those properties of currents are seldom precisely known by those who specify their other attributes.
Antenna currents are meant to radiate electromagnetic energy. And to better understand why it radiates, any current or any portion of a current can be viewed as an antenna current. In this book, therefore, an antenna current is defined to be any current or any portion of a current that is so viewed to better understand its tendency to radiate.
Clearly, antenna currents should not be included in electronic systems that are not meant to radiate. However, circuit currents are seldom viewed by their designers as antenna currents. The minimization of antenna-current behavior by circuit currents needs to be an integral part of circuit design. In other words, the total behavior of currents, not only their schematically defined behavior, must be a primary concern of circuit designers. Until that becomes standard design procedure, the effective control of unnecessary electromagnetic radiation ...