Tunable dual/triple band-pass filter based on stub-loaded resonators for wireless applications

Abstract

Compact dual/triple band-pass microstrip filters operated in wireless applications are presented in this paper. The proposed filter is consisting of two stub-loaded resonators (SLR) to achieve the band pass behavior with single band. By changing the capacitance of the open ended stubs, a second resonance mode can be introduced and controlled. The even mode of resonance can be controlled by inserting lumped capacitors at the open ends of the dual stubs. The proposed filter offers the possibility of creating fixed first pass-band and tunable second pass-band. The center frequencies of the lower and the upper pass-bands are adjusted to cover the WiMAX frequency bands centered at 3.5/5.3 GHz. In order to achieve the third frequency band centered at 8.1 GHz for ITU applications, another resonator is inserted in the dual tunable BPF. The prototype of the tunable dual/triple band filter is fabricated and measured to verify the simulation results and to demonstrate the validity of the proposed filter for wireless applications. The advantages of our proposed filters are lower insertion loss, small size and high selectivity.