Coplanar Stripline (CPS) Components

Abstract

Coplanar stripline (CPS) is a balanced uniplanar transmission line, consisting of two metallic conductor strips separated by a certain gap width, on a substrate. Conventional CPS does not provide bottom metallization of the substrate for ground; instead, one of the conductor strips provides electric ground of the other signal strip. This article investigates (1) CPS transmission‐line characteristics for practical circuit design and analysis using closed‐form equations; (2) CPS circuit components such as resonators, filters, and “tee” junctions; and (3) applications to antennas and wireless power transmission. Various new CPS resonators are modeled and designed and their performance investigated in terms of Q factor or bandwidth. As applications of the proposed CPS resonators, new CPS bandpass filters are demonstrated. The design methods of bandpass filters and their lumped‐element equivalent circuits are presented. A simple CPS lowpass filter is developed using interdigital capacitors and a CPS transmission line. For CPS component measurements, two types of broadband CPS‐to‐microstrip transition are introduced. Printed dipole antenna feeding can also be easily implemented using this transition. A novel CPS tee junction using coupled CPS (CCPS) is introduced. As an application of CPS tee junction, a twin‐dipole antenna fed by microstrip‐to‐CPS tee junction is presented at Ka band. A 1×8 printed dipole phased array is developed with the twin‐dipole antenna. Finally, as a circuit application of CPS, a dual‐frequency rectenna is developed at 2.45 and 5.8 GHz. For dual‐frequency rectenna components, a dual‐frequency antenna, CPS lowpass filter, and CPS bandstop filters are developed. To achieve high RF ‐to‐DC conversion efficiencies at both frequencies, diode analyses are performed for frequency‐insensitive high conversion efficiency.