970 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 45, NO. 6, JUNE 1997 Open- and Short-Circuit Terminated Series Stubs in Finite-Width Coplanar Waveguide on Silicon George E. Ponchak, Member, IEEE, and Linda P. B. Katehi, Fellow, IEEE Abstract— Open- and short-circuit terminated series stubs in finite-width coplanar waveguide (FCPW) fabricated on high- resistivity Si are experimentally characterized over the frequency range of 2–40 GHz. In coplanar waveguide (CPW), these stubs are typically placed in the center conductor, but in FCPW, the stubs may also be placed in the ground planes resulting in novel circuit elements with characteristics that make the stubs useful for matching circuits and filters. Equivalent circuit models for the stubs are presented, and it is shown that when the stub is in the ground plane the resonant frequency is equal, the inductance and resistance is halved, and the capacitance is double the values of the same stub in the center conductor. Furthermore, it is shown that by varying the stub position in the ground plane, higher Q stubs can be obtained. Index Terms— Bandpass filters, bandstop filters, coplanar transmission lines, coplanar waveguides. I. INTRODUCTION C OPLANAR waveguide (CPW) has proven to be a useful transmission line for millimeter-wave circuits, monolithic microwave integrated circuits (MMIC’s), and antenna feed networks because the top-side ground planes enable easy connection of series and shunt circuit elements without via holes. In practice, most microwave substrates are placed in a package or on a metal plate to facilitate heat removal and to provide mechanical support. Thus, a back-side ground plane is also present. It has been reported that power leaks from the CPW into the parallel plates created by the upper and lower ground planes [1], [2], resulting in box-type resonances [3], [4]. Several alternatives to avoid these resonances have been proposed: absorbing materials can be used to attenuate power at the edges of the circuit [5], multiple dielectric layers can be used to decrease the propagation constant of the parallel- plate waveguide mode which inhibits power coupling [1], via holes can be incorporated to short the upper and lower ground planes and create an effective box that has a higher resonant frequency [4], or the upper ground planes can be made nar- row with respect to the parallel-plate waveguide-mode wave- length to increase the resonant frequency out of the band of interest [3]. The last alternative, called finite-width coplanar waveguide (FCPW) (see Fig. 1), is attractive since it does not require extra Manuscript received October 8, 1996; revised February 28, 1997. G. E. Ponchak is with the Electron Device Technology Branch, NASA Lewis Research Center, Cleveland, OH 44135 USA. L. P. B. Katehi is with the Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109-2122 USA. Publisher Item Identifier S 0018-9480(97)03921-5. Fig. 1. Schematic of FCPW. (a) (b) Fig. 2. Schematic of short-circuit terminated series stubs (a) in the center conductor and (b) in the ground plane. processing steps to implement and does not alter the planar character of the line. Although open- and short-circuit shunt stubs in FCPW have been used in the design and fabrication of filters on GaAs [6], active antennas on Teflon fiberglass substrates [7], and instantaneous frequency-measurement units on Alumina [8], there has not been a characterization of the series stubs in FCPW. In this paper, an extensive experimental characterization of FCPW short- and open-circuit series stubs, which are implemented in novel ways and fabricated on un- thinned, high-resistivity Si substrates is presented, and several new and interesting results are discussed. 0018–9480/97$10.00  1997 IEEE