The Design Of Novel Broadband Band-stop Microstrip Filter

Defected Ground Structure (DGS) is proposed in recent years, that is etching periodic or non-periodic patterns in the ground plane of the microstrip transmission line. It is a structure which changes the current distribution in the ground, the distributed capacitance and inductance of the microstrip line. It has good band rejection and slow-wave characteristics. The DGS structure is relatively simple, small size and ease of processing. At the same time it has the effect of single-pole stopband and changing the characteristic impedance of the transmission line. It can play an important role in improving the performance of broadband band-stop filter filter, such as suppressing the harmonic response, enlarging rejection bandwidth, reducing the physical size of filter. Therefore, it is valued by more and more scholars.At first, the paper describes several traditional DGS structures:the rectangular DGS, dumbbell DGS and spiral DGS, and makes an comparion about them. Then the C-type of DGS structure is described, and the influence of various parameters on the filter transmission performance is analysed.Secondly, a metal cylinder loading structure is proposed on the basis of C-type DGS analysis. Compared with the conventional C-type DGS without the metal cylinder, it has obvious improved the bandwidth and stopband depth, which can not increase the size of the filter. And then the importance of the structure in miniaturization design is verified.Then, the cascaded C-type DGS structure is used in the design of broadband band-stop filter, which effectively improves the stopband depth and width, and the insertion loss of passband gets better.Finally, we design a new broadband band-stop filter by combining the cascaded C-type DGS with defect openings resonance loop, which gets enough bandwidth and in-band attenuation. The passband ripple is small and the change curve of the passband to the stopband is steep, so the inhibition properties of the signal can be greatly improved. Comparing the simulated and measured results through the design of new broadband band-stop filter, it verifies the validity and usefulness of this structure.