COMPACT DUAL-BAND BANDPASS FILTER BASED ON DUAL-MODE MODIFIED STAR SHAPED RESONATOR

In this article, a compact dual-mode dual-band bandpass filter with adjustable second passband using a star shaped resonator is proposed. It is loaded with two T-shaped stepped impedance stubs inside the resonator and these stubs introduce a transmission zero on the upper side of the first passband. A small triangular perturbation element attached to the star loop resonator excites dual degenerate modes and is responsible for the first passband with two transmission poles. Two U-shaped slots etched on the ground plane control second passband frequency which is derived from the first harmonic. It also helps in attaining two transmission poles in the second passband. Unlike, the conventional orthogonal feed used for dual mode filters, the proposed filter is fed by two arrow shaped feed lines oriented along the straight line and are parallel coupled to the resonator. Finally, a dual-mode dual-band bandpass filter is designed and fabricated for WLAN application and the dimensions of proposed filter are 16 mm x 17.32 mm. Measured results of the filter show good agreement with the Full-Wave simulated results. (C) 2017 Wiley Periodicals, Inc.