Research Of Multiband Filter Based On The CRLH Transmission Line

With the rapid development of communication technology and the increasingly shortage of frequency spectrum resources, more and more products of wireless communication are required to have highly performance. The multiband bandpass filter is an important component in front of communication system. The performance of filter directly affects the communication quality. Many bandpass filter research has the vital significance. In addition, as more and more requirement to the size of communication product, miniaturization has become the focus in the study of filter. Composite right/left handed transmission line(CRLH TL) with left-handed properties has the important application in miniaturization and high performance.The LC model of T-type structure is built as a CRLH TL. And parameters of the model are extraction. λ/4 transmission line and T-type structure are taken to design a tri-band filter. Then λ/4 transmission line is replaced by a T-type structure, a tri-band filter with five transmission zeros is generated. To miniaturized size of the multiband filter, a folding of SIR is taken to replace the open stub of T-type structure. At last, the designed compact filter has five transmission zeros. And its second passband can be tunable by adjusting the embedded T-type structure when designing.Models of the interdigital structure and the bandpss filter based on the CRLH TL are built. To generate a multi-band filter, an open stub is add to give a notch band. The center frequency of notch band is decided by length of the open stub in the middle.The complementary split ring resonator(CSRR) is modelled. Then, CSRR is loaded on the substrate integrated waveguide(SIW) structure with multiple models. And a dual band filter is produced. At last, to design a compact dual band filter, DGS are etch on an SIW with CSRR.The mushroom of CRLH TL is analyzed. To miniaturize the cell size, CSRR is taken to etch on bottom of mushroom structure. A compact bandpass filter is designed based on the small cell. Then the T-type structure and compact mushroom cell with CSRR are combined in parallel. A compact dual band filter with mutual independence is generated.All the design have been fabricated and measured. The good agreements between the simulations and measurements certify theory of this paper.