Low-profile circularly polarized microstrip patch antenna with pattern diversity

This letter presents a two-port circularly polarized pattern diversity microstrip patch antenna. The antenna is designed on a single layer with a low profile (0.021 lambda(0), where lambda(0) is the free-space wavelength at the central frequency). The broadside pattern and conical pattern of the antenna can be obtained by respectively exciting the fundamental mode of the inner circular patch and the high-order mode of the entire circular patch. With four pairs of silts on the patch, the antenna achieves circular polarization for both broadside and conical patterns. A prototype of it is fabricated and measured. The measured overlapped bandwidth of 10-dB return-loss and 3-dB axial ratio for both modes are 1.3% (1.569-1.580 GHz) and 0.6% (1.565-1.575 GHz), respectively. Moreover, the measured peak gain values are 6.4 and 3.7 dBi for broadside and conical modes, respectively. The satisfactory isolation (|S-21| < -22 dB) is also achieved between the two feeding ports in the common impedance matching bands.