Thin substrate broadband slotted spiral antenna with vertical interconnects

Monolithically integrated into a 3D MMIC (Multilayer Microwave Integrated Circuit) T/R module, a novel 2-arm Archimedean slotted spiral antenna was designed and fabricated for broadband operation in X-band. The antenna was processed on a thin polyimide substrate (68 um thick, 0.0038 lambdag) with a bottom ground plane. A vertically interconnected wideband stripline balun was used to feed the antenna. Both simulation and measurement results showed that performance of the slotted spiral antenna on thin substrates was improved when the slot width was reduced and became comparable to the substrate thickness. Return loss of less than -10 dB was measured for the spiral antenna throughout 2-18 GHz with the lowest value of -49 dB at 10.8 GHz. Uniform broadside radiation pattern was obtained with a gain variation of -12 similar to -1 dB. Also, near field power distribution was measured for a PCB version of the slotted spiral antenna with similar design parameters.