Millimeter-wave broadband transition of stripline and CPWG on thin-to-thick substrates

In many applications such as chip (or package) to PCB transition, due to the small pitch size of the chip (or package), very narrow 50 Ω; stripline or grounded coplanar waveguide (CPWG) is required. In order to reduce the line width, stripline or CPWG should be fabricated on thin substrate (in case of CPWG because minimum manufacturable gap is limited in normal low cost PCB technology). On the other hand using thin substrate increases metallic loss of CPWG and stripline, which is important especially at millimeter wave, and long channels, then it, is preferred to use thick substrate to reduce metallic loss. Also for many applications such as printed circuit antenna, thick substrate is preferred because it can increase the bandwidth and gain of the antenna. Then a broadband transition from stripline (or CPWG) on thin to thick substrate is needed. This paper presents a low-loss, broadband transition of stripline (and CPWG) on thin-to-thick substrates. Measurement results show that the proposed transitions have less than 0.1 dB insertion loss up to 40 GHz. Several TRL kits are used to de-embed the effect of connectors and probes.