Highly directive antenna systems are being sought to address the perceived needs of FutureG wireless systems and their applications. Practical alternatives to complex, power-hungry phased arrays are truly desired. A potential approach is to develop and employ compact superdirective systems. An endfire-radiating system is commonly said to be superdirective if its maximum directivity D_max surpasses the Harrington normal directivity bound: D_Harrington = (ka)² + 2 ka, where ka is the system’s overall electrical size. A broadside-radiating system is termed superdirective if its D_max > 4p A / l², where A is its (aperture) area orthogonal to the broadside direction and it is uniformly excited with a signal having the wavelength l.

      The concept of “needle” radiation and the accompanying abstraction of superdirectivity was introduced by Oseen in the physics community over 100 years ago. Numerous applied electromagnetics (EM) papers then followed over the last half of the last century that discussed the interesting attributes of unlimited directivity, i.e., superdirectivity, from arbitrarily small source regions and arrays. Nevertheless, the consensus in the EM community generally has been that superdirective systems are impractical for wide variety of reasons. However, a turning point in superdirectivity history occurred early this century with the successful demonstrations of electrically small, superdirective two-element endfire arrays of electric elements. Several superdirective multi-element endfire arrays of either electric or magnetic dipole elements have been demonstrated over the last decade.

      Those original theoretical notions of superdirectivity have been confirmed recently with explicit solutions of Maxwell’s equations based upon vector spherical wave expansion analyses. These solutions and the physics they have revealed will be discussed along with their implications for the engineering of practical superdirective systems. A multipole engineering paradigm has evolved that equips us with several practical approaches to realizing both superdirective broadside-radiating and endfire-radiating systems. They include unidirectional mixed-multipole antennas (MMAs) based on combinations of electric and magnetic near-field resonant parasitic (NFRP) elements that radiate multipole fields when they are excited by simple driven dipoles. Another strategy is to employ Huygens dipole antennas in a sector of a uniform circular array that are excited with custom-designed amplitudes to radiate mixtures of azimuthal eigenmodes. Yet another technique is to employ an MMA to excite both the electric and magnetic multipoles of a multilayered spherical dielectric lens that combine into unidirectional superdirective fields.

      The historical aspects of superdirective systems from the 20^th century and the electromagnetics – both physics and engineering features – of the 21^st century’s innovative realizations of practical superdirective systems will be reviewed. They encourage further superdirective research activities since they demonstrate that practical superdirective radiating systems are, in fact, achievable.