Differentially Fed Wideband Circularly Polarized Slot Antenna

This communication presents a novel design of a differentially fed wideband circularly polarized (CP) slot antenna. The CP antenna consists of two opposite-fed C-shaped radiating patches and a stub-loaded corner-truncated rectangular slot. With the slot designed to be antisymmetric with respect to the bisection plane and oppositely fed by two microstrip lines, good differential-mode (DM) performance was obtained. On the other hand, the radiations contributed by the corresponding parts of the antisymmetric CP antenna will be destructive when in common-mode (CM) operation. This results in high CM suppression without a preceding CM-rejection bandpass filter. Also, low DM axial ratios (ARs) were achieved by tuning the truncated corner length, the protruded stub length, and the coupling length and gap of the C-shaped radiating patches. The measurement shows that the designed CP antenna has a wide 10 dB DM impedance band of 5-6.49 GHz and a 3 dB DM AR band of 4.94-6.03 GHz, corresponding to a CP fractional bandwidth of 18.7%. Also, in 4.5-6.5 GHz, the proposed antenna can effectively reject CM input signals because the measured CM return loss is smaller than 2.91 dB, and can convert only very little DM input power into CM reflected power since the DM-to-CM conversion is less than -50 dB.