This document is an abstract from the 3rd International Scientific Conference on Applied Sciences and Engineering that took place in Bangkok, Thailand in July 2015. The abstract describes a comparative study carried out to estimate the performance of transmission line and cavity models of rectangular microstrip antennas mounted on six different dielectric substrate materials with variable substrate heights. An artificial intelligence technique called Adaptive Neuro-Fuzzy Inference System was used to optimize the length and width of the antennas. The simulation results predicted that the cavity model performs better than the transmission line model for thick substrates, while the transmission line model is better for low dielectric constants and thin substrates.