Miniaturized microstrip bandpass filter using coupled SCRLH zeroth-order resonators

A novel miniaturized microstrip bandpass filter has been proposed by using coupled simplified composite right/left-handed zeroth-order resonators. The SCRLH ZOR consists of microstrip transmission line sections, high/low-impedance short-line elements and grounded stub. Being one of the artificially metamaterials, the ZOR reonates when the phase constant equals to zero. Compared with the conventional half-wavelength resonator, the superiority of the ZOR mainly lies in its compact size. In addition, it is easy to tune the zeroth-order resonant frequency thanks to the simple structure and easy fabrication of the ZOR. In this paper, the performance and design of the ZOR is first studied in detail. Then the ZOR is exploited to devise a three-order Chebyshev coupled microstrip bandpass filter. Different coupling schemes are adopted including interdigital capacitor coupling for the interstages and aperture-backed dual-finger parallel-coupled line structures at the terminals, thus, the specified coupling strengths can be conveniently satisfied. Finally, a prototype device filter operative at S-band is provided to illustrate the proposed techniques. Salient feature of the size reduction of the novel filter is achieved (more than 70%) when compared to a conventional structure.