DGS is basically a technique to reduce the mutual coupling between the antenna elements of a MIMO antenna system. So it should be S12 parameter that gets affected with respect to antenna performance.

Hi

i agree with Anjali Chaudhari that mutual coupling between antenna elements is reduced with the use of DGS and S12 which is the coupling factor is affected . i suggest using a circular DGS shape to increase the gain

Hi,

Let's have some understanding of what is happening in the patch antenna first and then try to use DGS.

1) In patch antenna with the full ground plane, an image of patch current flows in the ground plane. This effectively cancels current on the patch. So the radiation decreases. This leads to the reduction in Gain. Also, the surface waves are trapped between Ground plane and patch contribute to the non-radiating loss. This also reduces gain.

2)When you create any defect in this ground plane, you remove the image current as well as reduce the surface wave. This, therefore, increases the radiation efficiency of the antenna which may increase gain.

3) However, it also increases the radiation on the backside, decreasing the directivity. So gain can reduce as well for some designs.

4) The point of Anjali and Majeed can now be readily understood. Since the surface waves traveling inside substrate are reduced, the coupling of energy from one antenna to other is also reduced. So if you are creating an array, reducing the mutual coupling can enhance the gain.

5) Effect on other parameters can also be understood now. With DGS, the energy stored decreases. So Q factor also decreases. Consequently, the bandwidth increases.

6) Since a part of metal is removed from the ground, lesser E fields are stored inside the substrate. Effectively the permittivity of substrate reduces. So the resonant frequency may shift to a little higher value.

7) Also, S11 may also reduce as the impedance matching is affected. You would need to tune your design to return your frequency to the original value and get good S11.

8) With this knowledge, try to cut the ground by looking at current distribution on the patch. Since you said it is the circular patch, most of the current will be on edges. So an annular / Circular DGS can work well. In fact, if you have some nulls in current, you can use C-shaped elements as well.

9) Finally, It will an EBG/AMC which can truly increase gain like nothing else. (With an exception of lenses / Partially reflecting surfaces/ Febry perot cavity).

Good Luck.