Design considerations in microstrip antenna fabrication

Deviations in effective electrical dimensions caused by slight variations in finished microstrip antenna length, variations in the relative permittivity of the substrate material or nonuniformity in the substrate thickness lead to discrepancies between the designed and actual resonant frequencies. This sort of discrepancy is especially significant because of the narrow bandwidth of such antennas. It is found that for low dielectric substrate microstrip antennas, the critical parameter affecting the change in resonant frequency is the error in antenna length while for high permittivity substrates, the tolerance in dielectric constant is the critical parameter.