Non-standard SIW techniques for modern applications: State of the art

• Comprehensive overview of Substrate Integrated Waveguide (SIW) technology. • Discussed design principles, loss mechanisms, and excitation methods. • Highlighted versatile SIW components: filters, antennas, couplers, amplifiers and more. • Explored SIW applications in IoT, biomedical sensing, and intelligent systems. Substrate Integrated Waveguide (SIW) technology has been one of the ground-breaking solutions in microwave and millimeter-wave engineering, combining high-performance features of conventional waveguides with cost-effective, low-profile, planar advantages of printed circuit technology. This work presents a detailed overview of SIW technology from its history of development and related principles, i.e, mode behavior, loss mechanisms, excitation techniques, and the role of substrate parameters. Various SIW-based structures are covered, such as passive and active devices like filters, couplers, multiplexers, power dividers, oscillators, mixers, amplifiers, and antennas. Advanced modified Substrate Integrated Waveguide (SIW) designs and manufacturing technologies are featured with enhanced performance, integration, and manufacturability. Special focus is directed toward multifunctional SIW devices with the aim of enabling the increasing use of miniaturized SIW sensors in Internet of Things (IoT) technology, particularly in environmental monitoring, agriculture, healthcare, and pharmaceuticals. Future research directions are aimed at the integration of SIW structures in next-generation communication systems, wearable devices, biomedical sensors, and intelligent wireless networks. The present review aims to equip researchers and engineers with a comprehensive understanding of SIW technology, its current capabilities, and its vast potential for future advances in high-frequency system design.