In this paper, a coaxially fed broadband U-slot stacked rectangular microstrip patch antenna in corporating a high and low dielectric material combination is presented. The antenna essentially consists of two commercially available microwave substrates (Rogers TMM3 and Rohacell HF71 foam). Dielectric constants of materials are 3.27 and 1.07 respectively. Foam material doesn't include copper surface thus a third dielectric substrate with thickness of 0.254 mm and dielectric constant of 2.2 is added over the foam material to ease of fabrication. The antenna return loss bandwidth is about 52.94%, centered about 3.4 GHz. The effect of the parameters, such as u slot length and width, on the antenna performance are determined, experimentally verified and discussed. © 2011 IEEE.