design of a compact balanced tri-band bandpass filter using simple planar resonator with wide stop-band and high selectivity

The most balanced multiband band-pass-filters have some remarkable properties while provide a trade-off between design goals. additionally, few of them have provided a structure capable of satisfactory harmonic suppression. stepped impedance resonators (sir) are famous and widely utilized to relocate or cancel high order harmonics, and they provide advantages when used in designing bandpass filters. they have shown benefits in achieving common mode (cm) suppression along with compact size and wide stopband. to design a tri-band balanced bandpass filter, a ring-sir structure is used as the main building block of the filter. the sir is first analyzed and the design formulas are presented and the design graphs are extracted based on that. using the graphs, it is possible to design a tri-band filter and have the ability to control the center frequencies of the pass-bands. to achieve high pass-band selectivity, coupled feeding configuration is chosen external quality factor is analyzed, and respective graphs are presented. results show more than 20db isol,ation with pass-bands centering at 1.7, 2.55, and 4.48 ghz, insertion losses of 1.44, 1.77, and 2.11 db respectively. the corresponding fbws are 3.95%, 4.10% and 1.56% respectively. great out-of-band performance is achieved with a wide stop-band stretching from 4.8 to 8.76 ghz. the cm rejection for three pass-bands are better than 12.9, 18.9 and 43.5db, respectively.