Aperture-coupled patch antennas are not as simple as they look: with proper modifications one can achieve a a variety of different performance metrics. For example:

• Wideband aperture-coupled microstrip antennas: by using a stacked patch structure and modifying input impedance
• Dual and circularly polarized aperture-coupled microstrip antennas: by introducing orthogonal/crossed feed slots
• High gain aperture-coupled microstrip antennas: by using stacked patches or combining antennas into arrays