Resonance features in the allowed and forbidden bands of microwave coaxial Bragg structures with periodically alternating dielectric filling

Background and Objectives: Microwave Bragg structures are used to create various types of microwave devices, including tunable resonators, directional couplers, miniature antennas, matched loads, various types of microwave filters with controlled characteristics. Coaxial Bragg structures based on coaxial elements, which are one of the most common types of microwave elements in waveguide systems, are characterized by a wide frequency range and the absence of radiation losses. Existing coaxial Bragg structures have significant dimensions or require irreversible structural changes to be made in their design. In this article, the opportunity to create a small-sized coaxial Bragg structure on the set of periodically arranged coaxial line segments with different dielectric filling is proposed. Materials and Methods: The transfer matrix of a complex quadrupole, which is a cascade connection of elementary quadrupole with known transmission matrices, was used to calculate the transmission and reflection coefficients of an electromagnetic wave in coaxial Bragg structures. For experimental studies, a measuring section was created in the form of a dismountable segment of the coaxial transmission line including a formed coaxial Bragg structure. Results: Amplitude-frequency characteristics of 11-layer coaxial Bragg structures without defects for different ratios of the electric lengths of the dielectric segments and 19-layer coaxial Bragg structures with the different defect location inside the structure for small 1.4 mm and large 19.26 mm defect lengths have been investigated. Conclusion: The сoaxial Bragg structure can be considered as several embedded in each other Bragg gratings with a different number of cells depending on the ratio of the electric lengths of elementary structural units. The frequency position of the defect mode in the coaxial Bragg structure with periodically alternating dielectric filling almost does not depend on the location of the defect inside the structure but on the electrophysical parameters of the defect. The amplitude of the defect mode is maximum for the defect located in the center of the coaxial Bragg structure.