Compact Folded Slot Antenna and Its Endfire Arrays With High Gain and Vertical Polarization

A novel folded slot antenna is proposed for the design of high-gain and compact endfire arrays. This letter shows that a planar slot antenna retains bidirectional radiation characteristics when folded into a compact structure. A folded slot antenna was designed in order to obtain a high endfire gain of 6 dBi. The proposed slot antenna's high gain makes it a good candidate for designing endfire arrays with vertical polarization. A series-fed technique is proposed in order to design two-element endfire and backfire arrays. Subsequently, an eight-element endfire array is proposed by combining endfire and backfire two-element arrays. The eight-element array is capable of producing a high endfire gain of 13.2 dBi with a size of 1.8λ0 × 1.4λ0, which is less than half the size of the existing endfire antennas with similar vertically polarized gain.