The effect of material loss on the axial ratio symmetry of circular microstrip patch antennas

Shorted annular ring patch antennas with two feeds supporting the first 4 modes are used to demonstrate the degradation of azimuthal axial ratio symmetry due to dielectric loss. An explanation of the effect is offered in terms of the attenuation of standing waves in a resonant cavity. A loss tangent comparable to common FR4 material (tan(δ) = 0.04) is shown to degrade axial ratio by 3 dB to 8 dB, depending on the mode number.