Defected ground structure

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Defected Ground Structure (DGS) is a purposely carved defect in the ground plane of a microstrip printed circuit board. It shows up as an etched pattern on the ground plane and acts like a small electromagnetic band-gap (EBG) feature. Unlike a full EBG, DGS uses a single defect or a few defects, arranged in periodic or aperiodic ways, to create a stop-band that blocks certain frequencies from propagating along the microstrip line.

The idea was introduced by Kim and colleagues, who used a dumbbell-shaped defect under a microstrip line to stop electromagnetic waves over a range of frequencies. Its compact size and easy fabrication made DGS popular, and many shapes were developed for microwave circuits. DGS has been used in filters, amplifiers, couplers, and power dividers, and under feed lines of microstrip antennas to filter out unwanted harmonics.

In 2005, Guha and co-workers showed how DGS could be applied to microstrip antennas to suppress cross-polarized radiation in circular patches by weakening higher-order TM21 modes, while keeping the main resonance intact. This non-resonant DGS concept opened up many developments in DGS types and geometries and cross-polar performance.

DGS has also improved antenna arrays. By integrating simple DGS, mutual coupling between array elements can be reduced, helping to avoid scan blindness in large phased arrays. The technique is now used in practical designs, including airborne and space-borne radars.