Packaged Microstrip Line: A New Quasi-TEM Line for Microwave and Millimeter-Wave Applications

In this paper, a new quasi-transverse electromagnetic (TEM) microstrip line, named as packaged microstrip line, is proposed for microwave and millimeter-wave applications. It is comprised of three dielectric substrates: a base layer to place the metal strip, a top layer to build the perfect magnetic conductor (PMC) shielding with periodic plated vias, and a middle layer to separate the PMC layer from the metal strip and the bottom ground plane. With the top PMC shielding, this novel microstrip line no longer suffers from issues of radiation losses, surface waves, or cavity resonances that exist in the classical microstrip line without or with a metallic shielding box. Also, the unwanted higher order mode created in the stripline by any vertical asymmetry between the ground planes will not be generated in the packaged microstrip line. In addition, the fundamental quasi-TEM mode will help this novel line avoid the mode conversion losses when integrated with other quasi-TEM lines, which happen to the substrate-integrated waveguide due to its fundamental TE
₁₀
mode. This paper focuses on the effects of the PMC-layer substrate on this line performance. We present how to adopt a proper substrate for each layer of the packaged microstrip line considering both stopband and transmission loss, and how to design the linewidth for a given characteristic impedance. Two different transition schemes of the packaged microstrip line to the standard microstrip line are taken into account. Two prototypes of the proposed packaged microstrip lines using different substrates for the PMC layer are fabricated. The measured and simulated results show good agreement.