Coplanar Stripline (CPS) Components

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. Keywords: coplanar stripline (CPS); CPS resonator; CPS filter; rectenna; dipole phased array