How exactly a ground plane helps inproving antenna gain? What is the logic behind it?
In microstrip patch antennas, a radiating patch sits above a substrate and below the substrate there is a ground plane. The ground plane is used for directing the electromagnetic energy in the forward direction. The ground plane is a conductor and metals reflect electromagnetic radiation. Usually, a copper is used as a ground plane with thickness of 35 micron. Some antennas are designed with etched ground plane. If you have an antenna with ground plane (microstrip antenna) and without ground plane (sometimes called monopole), the antenna with ground plane provides more gain than the one without ground. Whether to include ground or not depends on the application and radiation characteristics requirements.