Improvement of Compactness of Low pass and Band pass Filter Using a Simple Combination of Cross-Defected Ground Structure (DGS) and a Discontinuous Microstrip Line

Inhalt:
This paper presents a method to reduce the size of LPF using defected ground structure (DGS). DGS on the ground plane of transmission line such as microstrip provides a slowwave characteristics caused by its equivalent inductive and capacitive components. Due to this slow-wave effect, the electrical lengths of the microstrip lines, which are combined by DGS in matching networks, are longer than the original ones. Therefore, the physical length of microstrip line can be shortened by inserting DGS in order to keep the original electrical length and matching the same. The resultant length of the microstrip line with DGS are only 40% of the original lines in input and output matching networks, respectively. Additionally, a new suspended Layer’s technique will be used with DGS in order to reduce more the size and to suppress the second harmonic in reject band. In order to show that this idea is valid, two filters, of which one is designed using conventional DGS-method and the other is reduced using DGS and suspended Layer’s technique. Simulated and measured results of the proposed filters are presented and show good agreements.