The authors utilise a one-dimensional (1D) stack of three identical unprinted dielectric slabs as a superstructure to design a novel yet simple tri-band electromagnetic bandgap resonator antenna (ERA). The design, inspired from classical single-band 1D ERAs, is conceived by creating two resonant defects in the superstructure configuration to make it suitable for tri-band and high gain operation. A prototype, fabricated using FR4 material, is tested with a waveguide-fed slot antenna at 10.3, 11.9 and 13.7 GHz with a frequency ratio of 1.33:1.16:1. The slot feeds the cavity simultaneously in the three frequency bands and provides good impedance matching in each frequency band. Peak measured gains of 14.3, 13.4 and 16.1 dBi and radiation efficiencies of 83, 85 and 85% are achieved in the lower, middle and higher frequency bands, respectively.