A low-profile circularly-polarized sequential rotation fed $4\times 4$ array antenna working in the Ka-band from 27.5 GHz to 31 GHz is presented. The particularity of the antenna lies in its single-layer sequential rotation feed network implemented in a bed of nails using a combination of groove and ridge gap waveguides. The basic radiating element is one slot loaded by a simple coffee-bean-shaped parasitic element on top. Experimental results show an antenna matching below −10 dB in a 13.6% bandwidth and a measured axial ratio below 1.3 dB in the desired band.
