Dielectric EBG structure is an effective method to suppress the noise coupling in power distribution network (PDN) of multilayer printed circuit board (PCB). The usual dielectric EBG structure is formed by embedding high permittivity rods with circular or square cross-section shape into the substrate of PCB. Several discontinuous band gaps can be obtained within a certain frequency range, while wide and continuous forbidden frequency band is preferred. In this paper, a method of expand the bandwidth of noise isolation using rectangular EBG units is provided. To simplify the problem under consideration, the center distance and dielectric constant of EBG unit is held constant, only the size of rectangular EBG unit is varied. In the first case, either the length or the width of the rectangular is changed. In the second case, both the length and width of the rectangular are varied, while its area is kept constant. The calculated results show that by adjusting the aspect ratio of the rectangular EBG unit, two adjacent band gaps can be merged together, therefore, the width of a single band gap can be expanded significantly, and the continuous bandwidth with noise isolation degree better than -35 dB reaches up to 5.7 GHz within 15 GHz.