TABLE OF CONTENTS The historical roots of the planar integrated circuit go back to the 1940s, when V. H. Rumsey and H. W. Jamieson developed an antenna power divider (Figure 2.1) using a planar flat strip coaxial transmission line (Figure 2.2) [1]. Early in 1949, R. M. Barrett had the idea to employ the new transmission line not only to carry energy from point to point, but also to use it to make all types of microwave components, such as filters (Figure 2.3), directional couplers, hybrids, and matched loads (Figure 2.4). His results had first been published in 1951 [2, 3]. In 1952, D.D. Grieg and H. F. Engelmann announced another form of strip transmission line [4], now commonly known as microstrip, which was an adaption to the planar geometry of the two-wire line (Figure 2.5). In 1955 D. D. King announced the dielectric image line (Figure 2.6), which is an adaption of the dielectric waveguide to planar geometry [5]. Using this transmission line configuration, some circuit constructions for millimeter wave applications had become known in the 1970s. However, the dielectric image line did not find any broad application. In fact, the dielectric waveguides have become important in integrated optics [6]. Today, the microstrip line and the coplanar waveguide are considered the standard planar waveguiding structures in the microwave and millimeter wave region (see Section 2.1).
