Fabrication of hybrid shielded-stripline using half substrate integrated waveguide and half shielded-stripline structures

Abstract

A hybrid shielded-stripline (SS) for broadband TEM singlemode propagation up to 20 GHz is presented. Substrate integrated waveguide (SIW) technology is applied for designs of SS unhindered by the width and materials of the substrate. The hybrid structure, half SIW and half SS, which sandwich the buried-strip, is suggested for a simple fabrication. Therefore, the in-house vertical interconnection technique between two different planes on different substrates is proposed, which results in the realisation of the vias and the hybrid SS structures. The size of the hybrid SS, including transition, is 15.50 × 5.00 × 0.62 mm and the insertion loss is measured to be 1.45 dB/cm at 20 GHz.Introduction: A shielded-stripline (SS) is one of the planar type transmission lines for specific RF applications such as permittivity measurements (highly-sensitive-to-noise-systems) and security communications. It can implement TEM propagation, as well as high power and non-dispersive transmissions. A conventional SS consists of a buried-metal strip in the substrate (dielectric) which is surrounded by top and bottom GNDs, and metallic sidewalls. The surrounding GNDs screen the transmitted signal from external noise [1]. Its application, however, is still limited by complex fabrication and substrate design. Substrate integrated waveguide (SIW) technology can be applied to solve these difficulties and even offers a better integration capability by its planar nature. The SIW is synthesised by top and bottom GNDs surrounding the substrate with via-arrays. It shows similar field distribution to that of the rectangular waveguide [2]. Recently, an advanced study has proposed to propagate TEM waves by combining SIW with the conventional stripline, however, this still suffers from high cost and difficulties in fabrication owing to the via and multilayer structures [3].In this Letter, we propose the hybrid structured SS for a broadband TEM singlemode propagation using silicon micromachining and SIW technologies. The half SIW structure is applied to the design of SS for TEM singlemode propagation irrespective of the width and materials of the substrate up to 20 GHz. The in-house vertical interconnection technique, using sloped sidewalls, is suggested, which results in low-cost and simple fabrication for that multilayered structure and vias.