We propose some modifications in the conventional index-guided photonic crystal fiber (PCF) structure having circular holes of constant radii. In one of the proposed structures, the hole dimensions of the conventional PCF are modified such that the ratio of the radii of the holes in a particular layer with the nearest layer is constant while maintaining the same refractive index in all the holes. In the other structure, we propose to use different dielectrics in different layers of holes in the conventional PCF structure such that the ratio of the refractive index of the dielectric material in the holes in a particular layer with the nearest layer is constant. The simulations of the proposed structures are carried out using OptiFDTD simulator with full-vector mode solver using finite difference time domain method, and the results are compared with the conventional PCF structure having four layers of air holes. It is observed that the proposed structures exhibit lower waveguide dispersion and confinement loss than the conventional PCF structure over a wide range of wavelengths, making them suitable candidates for applications such as long-distance optical communications or high-data rate data transfer applications. One of the proposed structures exhibits large negative dispersion, and it can be used as a dispersion compensating fiber.