In this work, we present a new compact topology of interdigital bandpass filters implemented in coaxial waveguide

technology. Compared to classical coaxial resonators, which are typically loaded with cylindrical metallic posts, the resonators that we propose are based on rectangular cavities loaded with flat metallic strips of a finite thickness. The main advantages of the proposed topology are compactness and low-cost practical realization. The design process, which is based on the calculation of the input/output and the inter-resonator couplings, employs

the well-known Aggressive Space Mapping technique, with the aim of reducing the overall computation effort. In order to validate the new proposed topology and the design procedure, interdigital filters of orders 3 and 5 operating in the S-band have been designed. For validation purposes, the obtained results have been successfully compared to data provided by two different full-wave software tools (Ansys HFSS and CST Studio Suite).