Defected Ground Structure DGS


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Defected Ground Structure


Contents


Introduction

Abstract:Two microstrip designs based on spiral defected ground structures (DGS) are simulated using FEM and FDTD technologies in EMPro, and results are compared to measurement data.Defected Ground Structure technology makes intentionally designed defects in the ground plane, which creates beneficial inductive and capacitive effects on the designed structure. These additional networks can be used to introduce higher impedance, band rejection, and slow-wave characteristics to otherwise standard microstrip lines. The resulting microstrip structure can be significantly reduced in size compared to the conventional design. Figure 1 shows a microstrip transmission line design with a spiral array DGS on the ground plane.


Figure 1: Microstrip with a spiral array DGS

Design Challenges

There are typically no circuit models available for DGS structures in commercially available design tools. Therefore, the design and modeling of DGS structures require full-wave EM simulations. Since, with DGS structures, design perturbations are incorporated into the ground plane, the designs are no longer ideal, and designers must include the details of the ground plane defects in the EM simulations.

With EMPro's 3D EM simulators, designers can accurately predict the performance of DGS with both comprehensive frequency and time domain simulators within a single design environment.

Results

Figure 2 shows measured vs. simulated performance comparisons for the insertion loss characteristic of a microstrip transmission line with a spiral DGS array.


Figure 2: Measured vs. Simulated (Spiral DGS Array)

Figure 3 shows measured vs. simulated performance comparisons for the insertion loss characteristic of a microstrip transmission line with a single spiral.


Figure 3: Measured vs. Simulated (Single Spiral DGS)

Figure 4 shows electric field (E) plots for different frequencies with a spiral DGS array. As it is shown in the figure, the electric field is trapped within the DGS structure at the stop band frequency (band rejection).


Figure 4: Electric Field Plots

FEM and FDTD simulation technologies are complementary, with each having unique advantages. As shown in Figure 5, the TDR response can be directly obtained from FDTD simulation, which helps designers to understand the changes in the microstrip line impedance with the ground plane defects.


Figure 5: TDR of DGS

Conclusion

Both FEM and FDTD simulation technologies provide highly accurate 3D EM simulation results, enabling designers to develop and model DGS structures that improve the performance and reduce the size of their microstrip designs.

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