Design of multi-band microwave filter with asymmetric polygonal microstrip loops

Telecommunication industry requires a new generation of multifunctional devices, simultaneously operating under more communication standards, in multi-band microwave ranges, small size, compact, robust, and low cost. Microstrip RF/microwave technology can provide these features. In this paper a multi-band filter which consists of a compact microstrip topological structure is presented. It uses a quadri-port polygonal contour for coupling between degenerate modes propagating through the microstrip line network. A lot of resonant frequencies and bandpasses can be selected between the four ports. The simulated results show a dual-band response between the first two ports and a three-band response for the other two ports of the same physical structure. Originality of this article is based on the introduction sections of a transmission line between peaks of a polygonal contour with a small gap creating an asymmetry in network, instead of using concentrated constant elements. The new structure provides the possibility of microstrip full implementation and a larger flexibility for choosing of different band frequencies for practical applications.