Ground plane meandering in Z direction for spiral antenna

An antenna has a spiral driven element that meanders in a z direction, perpendicular to the x-y plane of the spiral, and a ground plane that also meanders in the z direction, such that spacing between the ground plane and the driven element is an odd multiple of one-quarter wavelength, along at least a portion of the length of the driven element. The spacing promotes constructive interference from signals reflected by the ground plane, increasing the front-to-back ratio of the antenna and, thereby, providing gain. The ground plane of a wideband version of the spiral antenna meanders, such that the spacing varies between about an odd multiple of one-quarter wavelength of an upper frequency to about an odd multiple of one-quarter wavelength of a lower frequency of a frequency range, thereby providing gain over a range of frequencies.