Broadband slotted spiral antennas with thin dielectric substrates

New broadband two arm Archimedean slot spiral antennas were designed and fabricated on very thin dielectric substrates with bottom ground planes. The antennas were designed for a vertically interconnected monolithically processed multilayer microwave integrated circuit. Two narrow-slot spiral antennas were fabricated and tested on a PCB first with a substrate thickness of 0.073 λg and 0.0056 λg, respectively. An operation bandwidth of 5.22% and 4.13% was achieved with good axial ratio and radiation pattern. Using the same design guideline, a 3^rd spiral antenna was then monolithically fabricated on a 68 μm polyimide substrate (0.0038 λg) with bottom ground plane. The return loss was below -10 dB from 5.96-15.10 GHz with the lowest value of -24.88 dB at 7.13 GHz. Both simulation and measurement results have shown that performance of the spiral antennas on very thin substrates was improved when the slot width became comparable to the substrate thickness.