Study of various shapes of the coupling slot in CPW-fed microstrip antennas

A numerical modeling based on the solution of coupled integral equations is used for the characterization of CPW-fed aperture-coupled microstrip antennas. Various shapes of excitation slots, such as open stubs, slot loops, and capacitively and inductively coupled slots, are investigated in terms of return loss and front-to-back radiated power ratio. It is shown that a centered CPW open stub gives a minimum of back radiation while allowing for easy matching. The slot-loop excitation seems to be a convenient feeding mechanism that also allows the insertion of active devices.