In this study forty-five X-bnd rectangular microstrip patch antennas fed by microstrip line using ${lambda}$/4 transformer were fabricated on teflon substrates with low high permittivities and varous thickness (substrate thickness : 0.6 ~ 2.4 mm, permittivities : 2.15 ~ 10.0), and effects of permittivity and electrical thickness on antenna characteristics were studied with measured return loss (1/S$_{11}$) and resonant frequencies. When substrate electrical thickness was greater than 0.060 ${lambda}_{0}$return loss was very good and genrally more than 20 dB, but resonance characteristics was somewhat unstable. The more than 0.088 ${lambda}_{0}$ the thickness was, the more unstable it was. As a result, in the rest range except 12, 13 GHz we had very good mesured return loss iwth greater than 20 dB, and in the range 7 to 9 GHz resonant frequencies were within $pm$2 % error, on ${epsilon}_{r}$=5.0, height = 2.4 mm substrate.