  High-gain antennas are essential hardware devices, powering numerous daily
applications, including distant point-to-point communications, safety radars,
and many others. While a common approach to elevate gain is to enlarge an
antenna aperture, highly resonant subwavelength structures can potentially
grant high gain performances. The Chu-Harrington limit is a standard criterion
to assess electrically small structures and those surpassing it are called
superdirective. Supergain is obtained in a case when internal losses are
mitigated, and an antenna is matched to radiation, though typically in a very
narrow frequency band. Here we develop a concept of a spectrally overlapping
resonant cascading, where tailored multipole hierarchy grants both high gain
and sufficient operational bandwidth. Our architecture is based on a near-field
coupled wire bundle. Genetic optimization, constraining both gain and
bandwidth, is applied on a 24-dimensional space and predicts 8.81 dBi realized
gain within a half-wavelength in a cube volume. The experimental gain is 6.15
with 13% fractional bandwidth. Small wire bundle structures are rather
attractive for designing superscattering and superdirective structures, as they
have a sufficient number of degrees of freedom to perform an optimization, and,
at the same time rely on simple fabrication-tolerant layouts, based on low-loss
materials. The developed approach can be applied to low-frequency (e.g.,
kHz-MHz) applications, where miniaturization of wireless devices is highly
demanded.
