Series fed patches work very well (and only then) when the two bands are well separated and the antennas present an effective short at each other’s bands of operation. Shunt fed patches work well (and only then) when both resonances are within a couple % of each other.
Higher Modes
So far, we’ve been talking about the fundamental TM10 mode. But, patch antennas are resonators and inherently exhibit higher modes.
Only a few TM modes are potentially useful and the other useful ones in a rectangular patch are TM20 and TM30. Other modes exist but result in exotic radiation patterns and have little -if any- practical use.
The radiation pattern cross sections of antennas operating in TM10, TM20 and TM30 modes have been plotted in Figure 23.