Small Size Defected Ground Structure (DGS) Coupled Resonator Band Pass Filters with Capacitor Loaded Slot Using FDTD Method

摘要

This paper presents a design of a small size second and third order band pass coupled resonator filters by using finite difference time domain method (FDTD). Two of the proposed filters consist of compact folded DGS resonators, the other consists of compact rectangular DGS resonators and a lumped capacitor is combined within the slot of each filter. The insertion of lumped capacitor within resonators increases the effective capacitance, and reduces the resonant frequency, so the dimensions of the filter will reduce and the performance of the filter will be improved by enhancing the energy stored in the resonator. The resonance bandwidth is decreased leading to increasing the resonator quality factor. A second order band pass filter with centre frequency of 2.4 GHz has been designed, fabricated and measured. The filter has a wide stop band with a rejection higher than 20 dB up to more than 10 GHz. Insertion loss of less than 0.7 dB is achieved within the pass band. Another second order band pass filter with centre frequency of 3.1 GHz has been designed, fabricated, and measured. The filter has a wide stop band with a rejection higher than 20 dB up to more than 10 GHz. Insertion loss of less than 0.8 dB has been achieved within the pass band. It is found that, the experimental results agree well with the EM-simulation and FDTD simulation results. Finally, a third order band pass filter with center frequency of 2.4GHZ with single transmission zero at 2.61 GHz is designed and simulated. The filter has pass band from 2.3 to 2.52 GHz and wide stop band with rejection higher than 20 dB up to more than 8GHZ, and insertion loss lower than 1 dB is achieved within pass band.