In an embodiment, an antenna array includes at least first and second antenna rings. The antennas in the first antenna ring are each spaced apart by approximately a first distance from a center of the first antenna ring. And the second antenna rings is approximately concentric and coplanar with the first antenna ring, and each antenna of the second antenna ring is spaced approximately a second distance from the center. For example, the antennas of the first antenna ring are spaced apart by half of a first wavelength corresponding to a first frequency of a frequency range over which the antenna array is designed to operate, and the antennas of the second antenna ring are spaced apart by half of a second wavelength corresponding to a second frequency of the frequency range.