Review of Substrate Integrated Waveguide Circuits for Beam-Forming Networks Working in X-Band

A Review on SIW and Its Applications to Microwave Components

Substrate-integrated waveguide (SIW) is a modern day (21st century) transmission line that has recently been developed. This technology has introduced new possibilities to the design of efficient circuits and components operating in the radio frequency (RF) and microwave frequency spectrum. Microstrip components are very good for low frequency applications but are ineffective at extreme frequencies, and involve rigorous fabrication concessions in the implementation of RF, microwave, and millimeter-wave components. This is due to wavelengths being short at higher frequencies. Waveguide devices, on the other hand, are ideal for higher frequency systems, but are very costly, hard to fabricate, and challenging to integrate with planar components in the neighborhood. SIW connects the gap that existed between conventional air-filled rectangular waveguide and planar transmission line technologies including the microstrip. This study explores the current advancements and new opportunities in SIW implementation of RF and microwave devices including filters, multiplexers (diplexers and triplexers), power dividers/combiners, antennas, and sensors for modern communication systems.

Substrate-Integrated Waveguide Microwave Sensor for Water-in-Diesel Fuel Applications

A water-in-diesel microwave sensor based on a substrate integrated waveguide (SIW) microwave applicator is designed and characterized in this study. The interaction between the microwave electromagnetic field and the diesel fuel contaminated with small concentrations of water is obtained via suitable radiating slots placed on the top of an SIW waveguiding structure. The SIW applicator working frequency is chosen by observing the behavior of the complex dielectric permittivity of the fuel–water blend based on a preliminary wide band investigation. The performances of the SIW microwave sensor are evaluated in terms of scattering parameter modulus |S21| as a function of the water concentration in ppm. The best sensitivity Δ|S21|Δρ=1.42 mdB/ppm is obtained at a frequency of f=9.76 GHz, with a coefficient of determination R2=0.94. The sensor is low-cost, low profile and ensures a good sensitivity for constant and real-time monitoring.

A Split Ring Resonator-Based Metamaterial for Microwave Impedance Matching with Biological Tissue

A metamaterial lens based on a split ring resonator (SRR) array has been designed and optimized to improve the focusing and the penetration depth in human biological tissue of a microwave beam irradiated by a substrate integrated waveguide (SIW) cavity backed patch antenna. The impedance matching of the antenna loaded with human tissue is strongly improved. The simulations have been performed by using CST Microwave Studio®. A prototype of the device has been fabricated with the printed board circuits (PCB) process and has been characterized using a Network Analyzer and an antenna measurement system in anechoic chamber. A novel microwave applicator for hyperthermia therapy of skin cancer could be developed. The performances of the proposed applicator have been evaluated in terms of measured S11 scattering parameter modulus and simulated power loss density. The obtained results indicate that an SRR-based metamaterial is a promising solution for external microwave applicators to employ in dermatology.