  Nanoantennas, operating at optical frequencies, are a transformative
technology with broad applications in 6G wireless communication, IoT, smart
cities, healthcare, and medical imaging. This paper explores their fundamental
aspects, applications, and advancements, aiming for a comprehensive
understanding of their potential in various applications. It begins by
investigating macroscopic and microscopic Maxwell's equations governing
electromagnetic wave propagation at different scales. The study emphasizes the
critical role of Surface Plasmon Polariton (SPP) wave propagation in enhancing
light-matter interactions, contributing to high data rates, and enabling
miniaturization. Additionally, it explores using two-dimensional materials like
graphene for enhanced control in terahertz communication and sensing. The paper
also introduces the employment of nanoantennas as the main building blocks of
Nano-scale Radar (NR) systems for the first time in the literature. NRs,
integrated with communication signals, promise accurate radar sensing for
nanoparticles inside a nano-channel, making them a potential future application
in integrated sensing and communication (ISAC) systems. These nano-scale radar
systems detect and extract physical or electrical properties of nanoparticles
through transmitting, receiving, and processing electromagnetic waves at
ultra-high frequencies in the optical range. This task requires nanoantennas as
transmitters/receivers/transceivers, sharing the same frequency band and
hardware for high-performance sensing and resolution.
