Effect of dielectric material tolerances on the performance of singly-fed circularly polarised stacked patch antennas

A method for the design of broadband circularly polarised (CP) patch antennas was recently proposed by the authors (Chung, K.L. and Mohan, A.S., IEEE Trans. Antennas and Propagat., vol.51, p.3239-48, 2003). Designs for both C- and Ku- band antennas made use of high permittivity materials as their grounded substrates. However, the high permittivity material suffers from a high tolerance (∼3%) in dielectric constant, making the design process more difficult. This work examines the substrate tolerance effects on the performance of the CP-EMCP antenna elements presented in the previous paper. The performance includes the input impedance characteristics (VSWR), impedance bandwidth (ZBW), antenna gain, axial ratio and axial-ratio bandwidth (ABW). Further, this paper supplements the information on the design of broadband CP-EMCP patch antennas that comprise hi-lo dielectric combinations. The tolerance effects in four extreme cases on the gain and impedance matching (VSWR) of both the C- and Ku-band designs are shown to be insignificant. However, these same effects are significant on the axial ratio and axial-ratio bandwidth in both designs. The tolerance in thickness of high permittivity materials causes a deterioration in the boresight axial ratio of singly-fed stacked patch antennas.