  Rapid developments in synthetic aperture (SA) systems, which generate a
larger aperture with greater angular resolution than is inherently possible
from the physical dimensions of a single sensor alone, are leading to novel
research avenues in several signal processing applications. The SAs may either
use a mechanical positioner to move an antenna through space or deploy a
distributed network of sensors. With the advent of new hardware technologies,
the SAs tend to be denser nowadays. The recent opening of higher frequency
bands has led to wide SA bandwidths. In general, new techniques and setups are
required to harness the potential of wide SAs in space and bandwidth. Herein,
we provide a brief overview of emerging signal processing trends in such
spatially and spectrally wideband SA systems. This guide is intended to aid
newcomers in navigating the most critical issues in SA analysis and further
supports the development of new theories in the field. In particular, we cover
the theoretical framework and practical underpinnings of wideband SA radar,
channel sounding, sonar, radiometry, and optical applications. Apart from the
classical SA applications, we also discuss the quantum electric-field-sensing
probes in SAs that are currently undergoing active research but remain at
nascent stages of development.
