A dual-band enhanced-bandwidth microstrip antenna is presented with a frequency separation of f2=f1 = 1:33. In order to
achieve the dual-frequency operation, a rectangular patch is loaded with a stub at one of its radiating edges. To improve bandwidth at each band, two parasitic patches are coupled to the driven element.
Anguera, J.; Puente, C.; Borja, C. Dual frequency broadband microstrip antenna with a reactive loading and stacked elements. "Progress in electromagnetics research letters", 2009, vol. 10, p. 1-10.