A 3-D Miniaturization Method for Low-Impedance Designs

Microstrip interconnects with a V conductor are designed, fabricated, and measured to provide a compact solution for designs requiring low characteristic impedance lines. S-parameter curves are shown up to 35 GHz for 0.5-cm-long lines. The 308-mum-deep V structure produces a 33.8-Omega line with strong standing waves and reflections under 5 dB. To further reduce the impedance, a partial shield is added that results in 6.7 times reduction of signal line width, near elimination of open-end effect, and excellent correlation with a standard 15-Omega microstrip up to 25 GHz. A filter demonstration shows near ideal behavior in the 3 dB response and low return loss when compared to a similar conventional design.