Vertically interconnected thin substrate broadband slotted spiral antenna for conformal phased arrays

A new broadband 2-arm Archimedean slotted spiral antenna was designed and monolithically fabricated as an integral part of a 3D MMIC (Multilayer Microwave Integrated Circuit) T/R module. The antenna was processed on a thin polyimide substrate (68 um thick, 0.0038 λg) with a bottom ground plane. A wideband stripline balun was vertically interconnected to the antenna. Return loss of less than -10 dB was measured from 6 to 14 GHz with a lowest value of -49 dB at 10.8 GHz. Uniform broadside radiation pattern was obtained across the X-band with a gain variation of -12 ∼ -1 dB. Both simulation and measurement results showed that performance of the slotted spiral antenna on a thin substrate was improved when the slot width became comparable to the polyimide substrate thickness. Also, reactive near field power distribution was measured for PCB slotted spiral antennas with similar designs. The low profile of the 3D MMIC T/R module enables the realization of the conformal phased array antenna systems.