Development of a New Equivalent Circuit of DGS with Ideal Transformer

In this paper, a new equivalent circuit of a rectangular dumbbell-shaped defected ground structure (DGS) with an ideal transformer is proposed. The proposed circuit incorporates a parallel resistor in the DGS gap, enabling the extraction of the coupling coefficient of DGS occurring in the narrow line gaps. Both circuit simulations and measurements demonstrate excellent agreement, confirming excellent performance compared to the measured results. Unlike the conventional equivalent circuit, which consists only of the lumped element, this one has an accuracy of only DGS units. In the proposed circuit, an ideal transformer has higher accuracy for the DGS in parallel with a resistor. We observed that increasing the resistance of the parallel resistor on the DGS unit leads to a decrease in the coupling coefficient and, conversely, decreasing the resistance prompts an increase in the coupling coefficient. The goal of this study is to develop a new equivalent circuit for a DGS unit with the ideal transformer, especially to find the coupling coefficient that occurred in the DGS gap. Here, we analyzed that the structure of the DGS unit had a gap, and the coupling coefficient must be built into any value. To demonstrate the effectiveness of the proposed circuit, DGS was used to design and conduct fabrication and measurement. The advantages of the proposed circuit analysis of the DGS behavior can be used to develop the attenuation pole as a one-pole low-pass filter, paving the way for future applications and developments in microwave and RF circuit design.