Compact microstrip bandpass filter with enhanced stopband performances

This work is focused on the development of new microwave filter structure for high selectivity applications. This type of design is very important to radio frequency engineer, since they are currently used in communications applications to reject spurious signals, and to separate different channels in multiplex systems. The idea presented in this article is based on pentagonal open-loop resonators, with the addition of tapped input/output (I/O) lines, to construct a high performance bandpass filter. The tapped I/O lines may have an independent extra transmission zero in the stop-band without requiring complex coupling between resonators. The full-wave simulator CST microwave studio was used to design the resonator and to calculate the place of tapped lines. The proposed filter was designed, fabricated and tested. The results of the tests showed that responses had a good agreement with the theoretical predictions.