Synthetic quasi-TEM meandered transmission lines for compacted microwave integrated circuits

Abstract

This paper presents a two-dimensional transmission line (2-D TL) that supports quasi-TEM propagation mode and reduces problems associated with compacted meandering of microstrip (MS) on propagation constants and the characteristic impedances commonly observed in conventional one-dimensional MSs. The proposed 2-D TL comprises two layers of metallic surfaces on either side of a dielectric substrate. The top metal surface is a meandered connection of a unit cell with a central patch and connecting arms. The bottom surface is a meshed 2-D periodical ground plane, whose etched portion complements the patch portion of the too surface, forming a complementary-conducting-strip (CCS) TL, enabling a combination of an MS and MS with the tuning septa in a unit cell. Both theoretical and experimental investigations of the CCS TL agree well and demonstrate that it is much less susceptible to the effects of meanderings on the propagation constant and characteristic impedance than an MS for the same meandered pattern. Two design examples are presented to demonstrate the potential for a CCS TL for miniaturizing microwave passive circuits with minimal losses. The first example involves a 5.4-GHz CCS four-port rat-race hybrid, realized in RO4003 and reduces the area of original MS design by 87%. The second example illustrates the applicability of a CCS TL to a monolithic RF integrated circuit using a first-pass design of a 5.2-GHz CMOS oscillator incorporating a CCS TL as a resonator with an area totaling 500 x 600 mum(2) including pads base on Taiwan Semiconductor Manufacturing Company's 0.25-mum 1P5M CMOS process techniques.