volume | PIER Journals

Abstract

In this paper, a miniaturized balanced bandpass filter characterized by biaxial symmetry is designed and implemented using four C-section parallel-coupled microstrip lines. As two orthogonal symmetric axes are inherently embedded across the filter layout, a natural geometric constraint is imposed and therefore furnishes two independent input/output port states. Owing to its symmetric topology, the developed filter replicates the same differential- and common-mode responses at each of its two independent input/output port pairs. To further enhance the common-mode suppression without compromising the differential-mode performance, a quarter-wavelength open-circuited stub is introduced onto the junction of one of the C-section parallel-coupled microstrip lines. By utilizing this stub, the common-mode suppression bandwidth is effectively broadened. Moreover, highly compact circuit sizes are achieved for the developed balanced filters, which is regarded as essential for their integration into modern miniaturized microwave communication systems. Finally, the feasibility of the proposed concept is verified through the design and fabrication of two prototypes, and good agreement is observed between the simulated and measured results.

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Dr. Chuan Shao

Dr. Xin Gao

Dr. Rong Cai

Dr. Xinnai Zhang

Dr. Kai Xu