On Surface-Wave Suppression of Differential Circular Microstrip Antennas

Differential microstrip antennas have received considerable attention in the design of highly integrated radio transceivers for wireless communications. A study of the surface waves excited by the single-ended and differential feeds is presented for the circular microstrip antennas. The cavity-mode theory and the dyadic Green's function method are combined to rigorously calculate the surface-wave field excited by each mode for the circular microstrip antennas under single-ended and differential feedings, respectively. The vertical monopole probe antenna is used to measure the TM
₀
-mode surface wave excited by the single-ended and differential circular microstrip antennas, respectively. The measured and calculated results confirm that the surface wave excited by the differential feeding is smaller than that excited by the single-ended counterpart.