Low-Profile Patch Antennas With Vertical Monopole-Like Radiation Patterns Based on Modified Capacitive Coupling Structures

A low-profile linearly polarized (LP) patch antenna with a vertical monopole-like radiation pattern is proposed in this letter. Modified capacitive coupling structure (MCCS) that is introduced to feed the patch antenna compactly enables the polarization flexibility without changing the near- and far-field characteristics much. Then, four curved branches are added around the circular radiating patch to employ a horizontal wave of the same amplitude and 90° phase difference, thus an antenna with circularly polarized (CP) characteristic is realized. In order to decrease the resonant frequencies of both the LP and CP antennas to the GPS l1 band, four shorted pins are adopted to connect the patch with the ground. Antenna prototypes are fabricated to verify the designs; the measured and simulated results are in good agreement. Both the LP and CP antennas own the feature of low profile (less than 0.05λ), which is a good candidate for GPS communication.