Stacked square-ring pin-fed patch
Image of the Stacked square-ring pin-fed patch.

While the simplicity and compatibility of the well-known rectangular patch antenna makes it very popular, the size and limited bandwidth often restricts its suitability for direct integration into circuit boards. The standard rectangular patch forms the basis for a number of antenna variations, typically introduced to overcome a particular shortcoming of the standard structure.

One approach to reduce the size of a patch antenna involves removing a rectangular area of metal from the patch center. While this lowers the resonant frequency, it also reduces the achievable bandwidth. This bandwidth reduction may in turn be countered by using a stacked arrangement comprising of a parasitic square-ring element mounted above an active/driven square-ring element. The parasitic element is added primarily to increase the impedance bandwidth - by introducing an additional resonance in the operating band - but also has the advantage of improving the gain of the antenna.

Typical total gain pattern at the center frequency
Typical reflection coefficient versus frequency comparison for three types of rectangular patches