Distributed feedback EBS in a coaxial cable by means of periodical mechanical section modification

Microwave filtering is an essential function required for signal generation, detection and processing. Narrowband, high isolation filters are needed for many applications such as antennas and power amplifiers. Since the introduction of electronic band-gap structure (EBS), many applications of EBS have been demonstrated where a spatially periodic perturbation of the waveguide gives rise to a stop-band [1]. In this paper we report the results of the application of fibre Bragg gratings (FBG) theory [2] to coaxial cable distributed feed-back structures. We have created a narrowband transmission filter by inscribing a distributed feedback (DFB) grating in the cable with a pre-specified phase-shift within the structure. We modify the mechanical dimensions of the cross section of the cable and induce a periodic change in the effective propagation index of the mode propagating in the cable.