An antenna for radio-frequency electronics can include an end-fire antenna and a planar antenna spaced from the end-fire antenna for diversity of direction and antenna coverage. The end-fire antenna can be for wideband low form factor applications and have a first metal layer, a second metal layer, and a dielectric layer between the first and second metal layers. An open cavity formed in the dielectric layer that is filled with air, the cavity defined by a pair of sidewalls that extend from an aperture of the cavity to a rear wall of the cavity, where the depth of the aperture is defined between the aperture and the rear wall. The cavity is formed by selecting the width of the aperture of the cavity and the depth of the cavity such that the antenna achieves the same gain during operation irrespective of a variation in the thickness of the antenna.