A Novel Broadband Dual Circularly Polarized Microstrip-Fed Monopole Antenna

A broadband dual circularly polarized (CP) planar monopole antenna is presented in this communication. The antenna is fed by dual orthogonal microstrip lines for polarization diversity. Circular polarization is achieved with a modified ground-plane structure and the isolation between the ports is improved by extending a protruded strip between the feed lines. L-shaped strips (LSSs) and inverted LSSs are designed along the radiating edges of the monopole. The combination of these two strips maximizes the axial ratio (AR) bandwidth, when they are placed <inline-formula> <tex-math notation="LaTeX">$\lambda _{g}$ </tex-math></inline-formula>/4 apart at center frequency of the CP band. This principle is verified by fabricating the prototype on a 1-mm-thick FR4 substrate with 32 mm <inline-formula> <tex-math notation="LaTeX">$\times32$ </tex-math></inline-formula> mm lateral dimension. From the experimental results, it is observed that the 3-dB AR bandwidth of the proposed antenna is 80.7% (3.74–8.8 GHz). The gain, return loss, and port isolation are higher than 1, 10, and 20 dB, respectively, within the CP band.