Differential feeding technique for mm-wave series-fed antenna-array

A differential feeding technique for a broadband planar antenna-array is presented. The antenna structure is composed of four parallel linear series-fed arrays of four microstrip patches. To cancel the beam tilt versus frequency, one side of the array is fed with in-phase signal, whereas the same out-of-phase signal feeds the opposite side of the array. A rat-race balun is especially designed to generate those two signals. In comparison with other feeding techniques, there is no need for a resistive load which is actually a problem at millimeter (mm)-wave frequencies. To validate the concept, a 60 GHz prototype etched on the TacLamPlus substrate is designed and measured.